Tesi sul tema "Soft Robot Materials and Design"

Ce travail de thèse propose une approche intégrée pour le développement de doigts pneumatiques en silicone destinés à la manipulation dextre. Basée sur une démarche comparative entre l'expérimentation et la prédiction numérique, l'identification des modèles de comportement du silicone permet de prédire le comportement du doigt pneumatique. La conception de celui-ci est alors guidée par simulation, avec pour objectif de réduire la dépendance du comportement du doigt à l'effet Mullins. La méthode de fabrication retenue, l'injection basse pression, permet la mise en place d'un processus de fabrication robuste par surmoulage des renforts rigides et de la base du doigt. La conception du doigt et de l'outillage est définie de manière à permettre la production de l'assemblage complet en une unique étape d'injection
This thesis proposes an integrated approach to the design of pneumatic silicone fingers for dexterous manipulation. Based on a comparative approach between experimentation and numerical prediction, the identification of silicone behavioral models allows the prediction of pneumatic finger behavior. The design is then guided by simulation with the aim of reducing the finger's dependence on the Mullins effect. The chosen manufacturing method, low-pressure injection molding, allows a robust overmolding process for the rigid reinforcements and the base of the finger. The finger and tooling are designed to enable production of the complete assembly in a single injection step

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 71-74).
This thesis presents the work accomplished in the design, experimental characterization and control of a soft batoid robot. The shape of the robot is based on the body of the common stingray, Dasyatidae, and is made of soft silicone polymers. Although soft batoid robots have been previously studied, the novelty brought by the present work centers around autonomy and scale, making it suitable for field operations. The design of the robot relies on the organismic consideration that the stingray body is rigid at its center and flexible towards its fins. Indeed, all mechanical and electrical parts are inside a rigid shell embedded at the center of the robot's flexible body. The silicone forms a continuum which encases the shell and constitutes the two pectoral fins of the robot. The core idea of this design is to make use of the natural modes of vibration of the soft silicone to recreate the fin kinematics of an actual stingray. By only actuating periodically the front of the fins, a wave propagating downstream the soft fins is created, producing a net forward thrust. Experiments are conducted to quantify the robot's swimming capabilities at different regimes of actuation. The forward velocity, the stall forces produced by the robot when it is flapping its fins while being clamped, and the power consumption of the actuation are all measured. The peak velocity of the robot is 0.35 body-length per second and is obtained for a flapping frequency of 1.4 Hz and a flapping amplitude of 30°. At a flapping frequency of 2 Hz, and an amplitude of 30°, the maximum stall forward force of the robot averages at 45 Newtons and peaks at 150 Newtons. Other data collected is used to better understand the hydrodynamics of the robot.
by Audren Damien Prigent Cloitre.
S.M.

Les matériaux élastiques peuvent se déformer de façon réversible de plusieurs fois leur taille initiale. Leur faible résistance à la fracture provient de la présence de défauts, qui lors de la déformation, entraînent la nucléation et propagation catastrophique d’une fissure, mécanisme qui reste mal compris. Cette thèse s’organise autour de deux axes : (i) le développement de nouvelles stratégies de synthèse de renforcement des élastomères, et (ii) l’étude, plus fondamentale, de la fracture dans des matériaux contrôlés modèles. Inspiré du renforcement structurel des réseaux multiples, nous avons développé deux nouvelles voies de synthèse d’élastomères renforcées : des composites à charges molles et inter-pénétrables de même nature chimique que la matrice, et des films de particules à réseaux interpénétrés synthétisées par polymérisation en émulsion. Nous avons obtenu des composites dont le durcissement à la déformation est contrôlable par la fraction volumique de particules dans la matrice. Les particules à réseaux interpénétrés obtenues par polymérisation en émulsion ont pu être fonctionnalisées pour pouvoir être connectées lors du séchage. Dans un second temps, nous avons travaillé sur des réseaux élastomères modèles contenant des mécanophores pour étudier leur fracture. Nous avons notamment amélioré une nouvelle méthode permettant la visualisation et quantification par microscopie confocal de rupture des chaînes du réseau, basée sur une activation de fluorescence lors de la rupture de liaison chimique. En variant la longueur initiale de l’entaille dans des échantillons du même réseau polymère, nous avons pu discuter les prédictions de la mécanique de rupture élastique au regard de l’endommagement par rupture de chaînes en pointe de fissure. En variant la maille des réseaux polymères, nous avons pu étudier les effets structurels du réseau sur la rupture de chaînes en pointe de fissure et discuter le modèle moléculaire de Lake et Thomas. Enfin nous avons observé in situ la formation d’une striction élastique dans des réseaux multiples. Nous avons quantifié localement la rupture de liaisons et le transfert des contraintes du premier réseau vers le deuxième. Ces nouveaux résultats seront utiles au développement de nouveaux modèles réalistes de la fracture des matériaux élastiques
Elastic materials can deform reversibly by several times their initial size. Their low resistance to fracture is due to the presence of defects, which during deformation, lead to the still poorly understood catastrophic propagation of a crack. This thesis is organized around two axes: (i) the development of new elastomers designs for toughening, and (ii) the more fundamental study of fracture in more conventional elastomeric networks. Inspired by the structural reinforcement of multiple networks, we have developed two new ways of synthesizing reinforced elastomers: firstly, composites with soft and interpenetrable fillers of the same chemical nature as the matrix and secondly, films made from particles of interpenetrated networks synthesized by emulsion polymerization. We obtained composites with tunable strain-hardening according to the volume fraction of particles in the matrix. The double network particles obtained by emulsion polymerization could be functionalized chemically, which allowed their connection by covalent bonds during the drying process. In a second stage, we investigated the mechanisms of fracture of model elastomeric networks with a newly developed method allowing the mapping and quantification of network damage by fluorescence confocal microscopy. By varying the initial notch length in samples of the same polymer network and quantifying chain scission at the crack tip, we were first able to discuss the validity of the predictions of elastic fracture mechanics. Then, by varying the chain length in the polymer networks, we were able to investigate the effects of changing the network structure on chain scission at the crack tip and discuss the molecular model of Lake and Thomas. Finally, we observed in situ the necking process in multiple networks and quantified the local bond scission accompanying the stress transfer from the first to the second network. These new results will be useful for the development of new molecular models of fracture of elastic materials

This practice-led research examines how the emerging role of the ‘material designer’ can enrich the design process in Human Computer Interaction. It advocates embodiment as a design methodology by employing tacit knowledge; focusing on a subjective, affective and visceral engagement with computational materials. This theoretical premise is explored by drawing on the fields of soft robotics, as well as transitive and programmable materials. With the advancement and democratisation of physical computing and digital fabrication, it is now possible for designers to process, or even invent and composite new programmable materials, merging both their physical and digital capabilities. This study questions how the notion of soft can develop a distinct space for the design of novel user interfaces. This premise is applied through a phenomenological understanding of technology development—as opposed to generating data which is solely reliant on observable and measurable evidence. Bio-engineered technologies such as electroactive polymer, pneumatic and hydraulic actuator systems are deployed to explore a new type of responsive, sensual and organic materiality. Here, traditional medical diagnostic applications such as microfluidics are transferred into the experimental contexts of textiles and wearable technology. Therefore, by thinking through physical prototyping, a bodily engagement with materials and the interpretation of the elements of water, air and steam; a designer can create a fertile ground for a polyvalent imagination. Together, this methodology is used as a qualitative system for collecting and evaluating data on the significance of design-led thinking in soft robotic materials. This research concludes that there are insights to be gained from the creative practice and exploratory methods of material-led thinking in HCI that can contribute to the commercial research and development fields of wearable technology. Outputs include a prototype box of ‘Invention Tools’ for textile designers and the identification and creation of the role 04 of embodied making in relation to the imagination. Further, soft composite hybrids, incorporating elastomers, have potential applications in colour, texture and shape changing surfaces. Thus, this thesis argues that it is within the creative soft sciences that the next advancements in soft robotics may emerge.

This work places itself in the field of textile design, weaving and interactive objects. It explores how the combination of solid and soft materials in a woven structure affect its flexibility and pliability. By integrating solid materials as a weaving material the work aims to propose an alternative context for woven structures, not necessarily becoming fabrics but rather objects that can be interacted with. The design process consisted of series of workshops where woven samples were made on a hand loom, weaving frame and by hand. The result are three woven structures each of which show of different flexibilities attained through the combination of solid and soft materials. The pieces are meant to be interacted with and can be shaped in various ways by folding, stacking or connecting parts of the structure. Combining solid and soft materials with the weaving technique shows the potential of interactive structures and objects which propose multiple functions, and can be developed further into products for interior design or play.

Soft robots are getting more and more popular in rehabilitation and industrial scenarios. They often come into play where the rigid robots fail to perform certain functions. The advantage of using soft robots lies in the fact that they can easily conform to the obstacles and depict delicacy in gripping, manipulating, and controlling deformable and fragile objects without causing them any harm. In rehabilitation scenarios, devices developed on the concept of soft robots are pretty helpful in changing the lives of those who suffer body impairments due to stroke or any other accident. These devices provide support in carrying out daily life activities without the need and support of another person. Also, these devices are beneficial in the training phase where the patient is going through the rehabilitation phase and has to do multiple exercises of the upper limb, wrist, or hand. Similarly, the grippers developed on the basic principle of soft robots are very common in the industries or at least getting common. Their advantages are a lot as compared to the rigid robotics manipulators. Soft grippers tend to adapt to the shape of the object without causing any damage to it, providing a stable grasp. It can also help reduce the complexity in the design and development, for example, underactuated. Underactuated grippers use the minimum number of actuators to provide the same function that requires more actuators with a rigid gripper. Also, the soft structure allows to design specific trajectories to complete a certain grasping and manipulation task. This thesis presents devices for rehabilitation and assistive application to help people with upper limb impairment, especially wrist and hand functions. These devices have been designed to provide the people, with limited capabilities of hand and wrist functions, to live their lives with ease without being dependent on any other family member. Similarly, I present different soft grippers and a soft environment that provides different advantages and can do various grasp and manipulation tasks. I have presented results for each device, rehabilitation and assistive devices are used by a patient suffering from stroke and having limited movement of wrist and hand function. At the same time, the grippers are supported with a set of experiments that provide deep insight into the advantages of each gripper in industrial applications.

The current thesis introduces novel tools via two photochemically induced ligations; [2+2] photocycloadditions and photouncaging reactions for light-controlled Staudinger-Bertozzi ligations. New chromophores were designed to provide a bathochromic shift for the activation wavelength of both reaction types to address the challenges that prevent these systems to be available for biological applications. In-depth photoreactivity studies using action plots revealed the exact wavelength dependent reactivity of the developed systems along with the effect of solvent and pH on the photoreactivity, which contributed to a fundamental understanding of these reactions. The applicability of these systems was demonstrated by hydrogel fabrication and surface patterning.

Legged robots have the potential to cover terrain not accessible to wheel-based robots and vehicles. This makes them better suited to perform tasks, such as search and rescue, in real-world unstructured environments. Pneumatically-actuated, compliant robots are also more suited than their rigid counterparts to work in real-world unstructured environments with humans where unintentional contact may occur. This thesis seeks to combine the benefits of these two type of robots by implementing design methods to aid in the design choice of a 16 degree of freedom (DoF) compliant, continuum-joint quadruped. This work focuses on the design optimization, especially the definition of design metrics, for this type of robot. The work also includes the construction and closed-loop control of a four-DoF continuum-joint leg used to validate design methods.We define design metrics for legged robot metrics that evaluate their ability to traverse unstructured terrain, carry payloads, find stable footholds, and move in desired directions. These design metrics require a sampling of a legged-robot's complete configuration space. For high-DoF robots, such as the 16-DoF in evaluated in this work, the evaluation of these metrics become intractable with contemporary computing power. Therefore, we present methods that can be used to simplify and approximate these metrics. These approximations have been validated on a simulated four-DoF legged robot where they can tractably be compared against their full counterparts.Using the approximations of the defined metrics, we have performed a multi-objective design optimization to investigate the ten-dimensional design space of a 16-DoF compliant, continuum-joint quadruped. The design variables used include leg link geometry, robot base dimensions, and the leg mount angles. We have used an evolutionary algorithm as our optimization method which converged on a Pareto front of optimal designs. From these set of designs, we are able to identify the trade-offs and design differences between robots that perform well in each of the different design metrics. Because of our approximation of the metrics, we were able to perform this optimization on a supercomputer with 28 cores in less than 40 hours.We have constructed a 1.3 m long continuum-joint leg from one of the resulting quadruped designs of the optimization. We have implemented configuration estimation and control and force control on this leg to evaluate the leg payload capability. Using these controllers, we have conducted an experiment to compare the leg's ability to provide downward force in comparison with its theoretical payload capabilities. We then demonstrated how the torque model used in the calculation of payload capabilities can accurately calculate trends in force output from the leg.

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Water leaks pose a major problem of efficiency and cost to municipalities and industries that cover significant area. While current commercial methods to address these problems do not provide convenient or low cost methods to detect leaks, a soft-body pipe leak detection robot has been developed to traverse small, 50mm diameter water pipe systems. This robot has proven to be effective in small diameter pipes, but its scalability for large diameter pipes is unknown. The focus of this thesis is to scale up the leak detection robot for 300mm diameter pipes and fabricate a robot prototype. In particular, the relationship between the shape of the robot and its maneuverability was explored, such that it was designed to passively travel through the pipe, driven by water flow. The robot was designed to successfully pass through changes in pipe diameter, pipe bends, and through partially clogged regions. To detect and distinguish pipe leaks from other debris in the pipe, two sensors were integrated in the robot. Experimental testing was conducted with the robot to verify functionality of its leak detection sensors. Supporting electronics were also implemented to wirelessly charge and communicate with the robot.
by Kyle Scott Saleeby.
S.B.

Recently induction cookers, which are based on induction heating principle, have become quite popular due to their advantages such as high energy efficiency, safety, cleanliness, and compact size. However, it is widely known that with current technology, induction cookers require the cookware to be made of magnetic materials such as iron and stainless steel. This is why a lot of cookware is labeled â Induction Readyâ on the bottom. The limited choice of â Induction Readyâ cookware causes inconvenience to customers and limits the growing popularity of the induction cooker. Therefore, a novel induction cooker, which can work for non-magnetic material cookware such as aluminum and copper, can be very competitive in the market. This thesis studies the induction cooking application; briefly introduces its fundamental principle, research background and the motivation of the development of a non-magnetic material induction cooker. Followed by the research motivation, three commonly used inverter topologies, series resonant inverter, parallel resonant inverter, and single-ended resonant inverter, are introduced. A comparative study is made among these three topologies, and the comparative study leads to a conclusion that the series resonant inverter is more suitable for non-magnetic material induction cooking application. The thesis also presents several major issues about non-magnetic material induction cooking and how to deal with these issues through induction coil design, higher operating frequency and novel control strategy. Because of non-magnetic materialâ s low resistivity and permeability characteristics, it is difficult to be heated and to achieve soft-switching while the coupling between the induction coil and the cooking pan can be easily changed. Later in this thesis, these issues will be discussed in detail and some potential solutions to these issues such as self-sustained oscillating control, optimized induction coil design, proper selection of power semiconductor device, etc. A 1.5 kW high frequency series resonant inverter with self-sustained oscillating control is prototyped. Experimental results demonstrated successful operation of the resonant inverter under up to 1.5 kW, and the inverterâ s capability to maintain zero-voltage turn-on during wide operating condition is confirmed. At the end, a summary is given about the research work done in the thesis and future research work is discussed.
Master of Science

The innovation of rehabilitation and assistive technology nowadays is now driven by a double thrust. On one side, the average age of people is increasing as a result of the improved lifestyle in the last twenty years, which focuses on human well-being, consequently, the overall social impact of chronic diseases related to the musculoskeletal and nervous system is becoming relevant. On the other side, technology, spreading more and more now in everyday life, is acquiring an increasingly important role in preserving and ensuring a high quality of life even in the presence of temporary and/or chronic disorders. Technological advancements in the healthcare medical rehabilitative and assistive system allow people with disabilities to live a life in many cases independently. These advances, which translate into the realization of new devices and supports for the individual, can help in the autonomy of Activities of Daily Living (ADLs), in communication, study, learning, and more generally, to increase the degree of self-esteem by facilitating social inclusion and participation. The aim of this thesis is to combine aspects of robotics with the themes of assistance and rehabilitation, presenting new solutions in the Human Robot Interaction (HRI) field. In this manuscript, concerning rehabilitation and assistance, two major robotics areas are investigated, i.e. the exoskeleton and the haptic fields. The upper limb plays an important role in all daily activities. This thesis presents devices for rehabilitation and assistive application to help people with upper limb impairment, especially wrist and hand functions. The charm of these technologies lies in the possibility of following a rehabilitation path from home comfort, improving the medical health system, facilitating ADLs by eliminating constraints in terms of time, physiotherapist’s strength and costs, improving the rehabilitation path process. In this context, the exoskeletons, first for the wrist, then for the hand and finally an integration of the two just mentioned, are presented in the first thesis part. A user--centered design perspective is used throughout all design and development phases of the prototypes showing the effectiveness of developing tailor-made devices specifically designed on the user’ needs. Further, by exploiting haptic for rehabilitation and assistance, portable haptic grounded devices and wearable, are reported. Also, in this case, the focus of the thesis is on the hand providing solutions that can be used to help people in recovering and performing rehabilitation from remote without the physical presence of a doctor/specialist. Moreover, with regard to the topic of assistance only, the field of robotic grippers is exploited. Advanced design and manufacturing techniques are opening up opportunities in various technological applications, including end-effector design. In this context, grasping and manipulating objects in unstructured environments by means of simple, yet versatile and robust grippers and hands, is still an open challenge. In this thesis, it is presented a methodology for designing soft-rigid grippers that exploits compliant structures and implements a new type of actuation to vary its rigidity, able of performing different manipulation tasks. Similarly, in the final part of the thesis it is presented a soft-rigid gripper that combines a compliant and safe structure with a synergy between tendon and magnetic actuation for dressing assistance, which provides various advantages and can perform various grasping and manipulation tasks.

This thesis provides a detailed study on optimisation of cementitous treated soft clay soils in the South East Queensland region. A comparative study has been performed comparing the behaviour of cement and lime treated compressible clays from both Bangkok and South East Queensland. The purpose of the comparative study was to evaluate change in strength properties of treated soft clay soil as well as providing parameters for case studies using different analysis methods. This thesis compares the behaviour of soft clay treated with cementitous materials in South East Queensland and Bangkok. Overall it was concluded that the addition of cement and lime has favourable effects on the strength characteristics of South East Queensland soft clays.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Engineering
Science, Environment, Engineering and Technology
Full Text

The focus of this dissertation is on refining atomic force micrscopy (AFM) methods and data analysis routines to measure the viscoelastic mechanical properties of soft polymer and biological materials in relevant fluid environments and in vivo using a range of relevant temperatures, applied forces, and loading rates. These methods are directly applied here to a several interesting synthetic and biological materials. First, we probe poly(n-butyl methacrylate) (PnBMA), above, at and below its glass transition temperature in order to verify our experimental procedure. Next, we use AFM to study the viscoelastic properties of coating materials and additives of silicone-based soft contact lenses in a tear-like saline solution. Finally, a major focus in this dissertation is determining the fundamental mechanical properties that contribute to the excellent sensitivity of the strain sensing organs in a wandering spider (Cupiennius salei) by probing under in vivo conditions. These strain-sensing organs are known to have a significant viscoelastic component. Thus, the cuticle of living spiders is directly investigated in near-natural environments (high humidity, temperatures from 15-40 °C). The main achievements of these studies can be summarized through the following findings: We suggest that full time-temperature-modulus relationships are necessary for the understanding of soft materials systems, and present a practical method for obtaining such relationships. These studies will have a direct impact on both scientists in the metrology field by developing practical experimental procedures and data analysis routines to investigate viscoelastic mechanical properties at the nanoscale, and future materials scientists and engineers by showing via spider mechanosensory systems how viscoelasticity can be applied for functional use in sensing technology.

This research work addresses the application of Additive Manufacturing (AM) technologies in novel electrical machinery. The unrivalled design freedom offered by AM has the potential to revolutionise the way rotating electrical motors are designed and manufactured. The thesis investigates the possibility offered by AM to advance the design of electrical machines for lightweight and high performance, with potential in several industrial sectors, including automotive and aerospace. In particular, we investigate how the performance of electrical motors can be improved by manufacturing the soft magnetic rotor core using Selective Laser Melting (SLM) and how the consequent design choices affect the component's performance from a torque-to-weight perspective. First, the metallurgical and soft magnetic properties of high-silicon steel (Fe-6.7%wt.Si) parts produced by Selective Laser Melting (SLM) will be characterised and discussed as function of the processing parameters and post-processing heat-treatments. The results of this research show that, by means of SLM, high-silicon steel parts with permeability (above 24000) and hysteresis loss (coercivity below 20 A/m) comparable to the ones of laminated high-silicon iron can be produced. Then, FEM-based modelling and Topology Optimisation (TO) will be employed to design the rotor core of a surface-mount Permanent Magnet (PM) machine in order to achieve maximum torque-to-weight ratio while maintaining structural integrity. Importantly, three-dimensional FEA results show that the weight of an existing PM rotor core can be slashed by 50% without affecting its torque performance when the proposed TO scheme is employed and the actual mechanical and magnetic properties of the SLM material are considered. Finally, we suggest that further research should be aimed at extending the range of applicability of the proposed TO scheme to other machine topologies (i.e., Synchronous Reluctance), as well as at the adjustment of the alloy's chemistry for improved ductility to avoid the risk of in-process cracking.

Le but de ma thèse a été de concevoir des matériaux chimio-mécano répondants, des matériaux capables de permettre une transformation chimique réversible lorsqu’ils sont soumis à un stress mécanique. Tous les systèmes conçus ont été développés sur des substrats en silicone. Une première approche a consisté à créer des surfaces à sites cryptiques où une biotine est enfouie dans des brosses de chaines de poly(éthylène glycol). Le système streptavidine/biotine a été utilisé comme modèle. Ces surfaces sont anti-adsorbantes à la streptavidine sauf lorsqu’elles sont étirées à 50% où la biotine est reconnue mais les surfaces sont non réversibles. Dans une seconde approche, nous avons modifiés la surface du silicone par adsorption d’une multicouche de polyélectrolytes. Cette stratégie est basée sur la réticulation covalente du film par l’enzyme β-galactosidase modifiée. Nous sommes ainsi parvenus à créer une surface présentant une activité catalytique modulable par l’étirement mécanique, et ce, d’une façon partiellement réversible. Ce travail représente le premier exemple d’un système où une contrainte mécanique imposée à un matériau permet la déformation conformationnelle d’une enzyme et ainsi la diminution de l’activité catalytique. Dans une dernière approche, nous avons conçu un système mixte composé d’un substrat de silicone sur lequel un gel de polyacrylamide est greffée de façon covalente. Des enzymes ou des mécanophores pourront ainsi être inclus dans le réseau polymérique du gel de polyacrylamide et être étirés. Nous sommes parvenus à préparer de tels systèmes où l’hydrogel reste solidaire du film de silicone, sans apparition de craquelures jusqu’à 50%d’étirement
The goal of my PhD was to develop new routes to design chemo-mechanoresponsive materials, materials that respond chemically to a mechanical stress, in a reversible way. All the systems designed during my PhD thesis were based on the functionalization of silicone sheets. First we created cryptic site surfaces by embedding biotin ligands into PEG brushes. The couple streptavidin/biotin was used as a model system. At rest, the surface so-prepared was antifouling and biotin ligands were specifically recognized by the streptavidin when the surface was stretched at 50%. Unfortunately, in this first approach, the mechanosensitive surface did not lead to a reversible process. In a second approach, we modified the silicone surface by using the polyelectrolyte multilayer (PEM) film deposition. This strategy was based on the covalent cross-linking of modified enzyme, the β-galactosidase, into the PEM. We succeeded in modulating the enzyme activity in the film under stretching and this approach appears as partially reversible under stretching/unstretching cycles. This work represents the first reported system where enzymatic activity can be modulated by stretching due to modulation of the enzyme conformation. In a last approach, we also designed a mixed system consisting of a silicone sheet onto which a polyacrylamide hydrogel is covalentlyattached with the goal to create a stretchable gel into which one can covalently attach enzymes or chemical mechanophores. These enzymes or mechanophores can thus be put under mechanical stress. We succeeded in creating a system that can be stretched up to 50% without detachment of the gel from the silicone and without inducing cracks in the gel

The thesis deals with the development of a new hysteresis model and the design of observers for systems with non-monotonic nonlinearities and for a clas of two-degre-of-fredom Euler- Lagrange systems (2-DOF robot). Hysteresis modeling is useful to design new smart-materials based devices, as Nitinol stent of comon use nowadays in many surgical aplications, and to improve the control of hysteretic actuators. The new model, named generalized constructive model, is able reproduce a wider clas of hysteresis nonlinearities than some of the most known models as the Clasical Preisach, the Nonlinear Preisach and the Prandtl-Ishlinski (PI) models, describing a larger number of materials. The new model is developed by an algorithm that makes use of hysteresis minor lop chords, minor lops arisen from reversal branches up to n-order. This aproach that does not make use of analytic functions, adjusting their parameters fit experimental measurements, alows to relax the hysteresis properties of equal minor lops and equal vertical chords, required by the Clasical and the Nonlinear Preisach models, buthat do not hold for a number of smart materials. Four version of the model have ben described analyzed and new les constraining properties have ben introduced to state the representation theorems of the model. The price to be paid for such wider aplicability and precision are the greater experimental measurements that ned to be colected. By mean of numerical simulations acuracy new model is compared with respecto the Clasical, Nonlinear and PI models, showing higher precision, even in the case of the experimental hysteresis temperature versus electrical resistivity of the Nitinol wire shape memory aloy. Numerical solutions for the model implementation and a rate-dependent version, for hystereses that depend also by the input rate, are proposed. To complete first part of the thesis, an academic example of a two link planarobot, which motors have ben idealy substituted by shape memory aloy actuators, show the importance of the hysteresis modeling to control such actuators. The second part of the thesis deals with reduced order observer design for nonlinear systems. observer design is derived aplying the Imersion and Invariance (I&I) technique, recently introduced in literature. This technique alows to estimate a subset of the system variables overcoming isues arisen by high gain aproaches. The design requires solution of partial diferential equations (PDEs) joined to the estimation eror definition and dynamics. This technique, asumed that solutions PDEs are obtained, is more general and alow to cope with systems for which other clasic aproaches, as the ones based on the pasivity of the estimation eror system and circle criteria based, fail for conservativenes. Then, it has ben defined a global observer for a clas of systems with non-monotonic nonlinearities, and in particular for clas of Euler-Lagrange systems with tre like mechanical configurations (robots), achieving global convergence of thestimation eror. A separation principle for the later systems is proposed with computed torque and nonlinear PD-like terms controlaw by mean of Lyapunov-based tols. Numerical simulationshown the performances of the proposed observer and the output fedback design.

The mechanical properties of biological tissues are of increasing research interest to disciplines as varied as designers of protective equipment, medical researchers and even forensic Finite Element Analysis (FEA). The mechanical properties of biological tissue such as skin are relatively well known at low strain rates and strains, but there is a paucity of data on the high rate, high strain behaviour of skin - particularly under biaxial tension. Biaxial tensile loading mimics in vivo conditions more closely than uniaxial loading [1, 2], and is necessary in order to characterise a hyper-elastic material model[3]. Furthermore, biaxial loading allows one to detect the anisotropy of the sample without introducing noise from inter-sample variability - unlike uniaxial tensile testing. This work develops a high strain rate bulge test device capable of testing soft tissue or polymer membranes at high strain rates. The load history as well as the full field displacement data is captured via a pressure transducer and high speed 3D Digital Image Correlation (DIC). Strain rates ranging from 0.26s −1 to 827s −1 are reliably achieved and measured. Higher strain rates of up to 2500s −1 are achieved, but are poorly measured due to equipment limitations of the high speed cameras used. The strain rates achieved had some variability, but were significantly more consistent than those achieved by high rate biaxial tension tests found in the literature. In addition to control of the apex strain rate, the bi-axial strain ratio is controlled via the geometry of the specimen fixture. This allowed for strain ratios of up to 2 to be achieved at the apex 1 . When testing anisotropic membranes, the use of full field 3D DIC allowed for accurate and efficient detection of the principal axis of anisotropy in the material. No skin is tested, but instead three types of polydimethylsiloxane (PDMS, ”silicone') skin simulant are tested. These simulants were chosen to fully encapsulate the range of mechanical behaviour expected from skin - they were chosen to have stiffness's, strain hardening exponents and degrees of anisotropy significantly above or below the behaviour exhibited by skin. This ensured that the device was validated over a wider range of conditions than expected when testing skin. A novel approach to specimen fixation and speckling for silicone membranes is developed, as well as a fibre reinforced skin simulant that closely mimics the rate hardening and anisotropic behaviour of skin. In addition to bulge tests, uniaxial tensile tests are conducted on the various simulant materials in order to characterise their low strain rate behaviour. The composite skin simulant is characterised using a modified version of the anisotropic skin model developed by Weiss et al (1996) [4], and the pure silicone membranes are characterised using the Ogden hyper-elastic model.

For small diameter (<6 mm) blood vessel replacements, lack of collaterals and vascular disease preclude homografts; while synthetic analogs, ePTFE, expanded polytetrafluoroethylene, and PET, polyethyleneterephathalate, are prone to acute thrombosis and restenosis. It is postulated that the hierarchical assembly of cell populated matrices fabricated from protein analogs provides a new design strategy for generating a structurally viable tissue engineered vascular graft. To this end, synthetic elastin and collagen fiber analogs offer a novel strategy for creating tissue engineered vascular grafts with mechanical and biological properties that match or exceed those of native vessels. This work details techniques developed for the fabrication of prosthetic vascular grafts from a series of extracellular matrix analogs composed of nanofibrous collagen matrices and elastin-mimetic proteins, with and without cells, and subsequent evaluation of their biocompatibility and mechanical properties. The work details the fabrication and mechanical analysis of vascular grafts made from aforementioned protein analogs. Subesequent studies detail seeding and proliferation of rodent mesenchymal stem cells on protein-based composites to recapitulate the media of native vasculature. Finally detailing in vivo biocompatibility and stability of tissue engineered vascular grafts.

This article introduces a versatile control board design that can be used in many drying systems using direct heat transfer solutions in combination with static tray distribution based on development of a flexible self-tuning PID controller. The product is applied for a small oven drying solid waste samples or plant materials for further analysis of some parameters. The control board is built based on the Arduino embedded system using a flexible soft PID (Proportional–Integral–Derivative) controller that can automatically change its gains according to the required temperature thresholds to best meet the setpoint of temperatures. The system has a small steady-state error (SSE), fast response to the setpoints and keep stable with temperature deviation when reaching the required threshold around ± 0.5 0C. In addition, the controller board can operate in a variety of modes, including direct temperature operation, pre-set operation, and switching mode.
Bài báo này giới thiệu một thiết kế mạch điều khiển đa năng có thể áp dụng trong nhiều hệ thống sấy sử dụng các giải pháp truyền nhiệt trực tiếp kết hợp phân phối khí kiểu khay tĩnh trên cơ sở phát triển bộ điều khiển PID mềm tự chỉnh linh hoạt. Sản phẩm được ứng dụng cho một mô hình lò nhỏ sấy mẫu chất thải rắn hoặc mẫu thực vật phục vụ các nghiên cứu phân tích thành phần một số chất. Mạch điều khiển được chế tạo trên nền tảng hệ thống nhúng Arduino sử dụng bộ điều khiển PID mềm linh hoạt, có khả năng tự động thay đổi tham số theo ngưỡng nhiệt yêu cầu để đáp ứng nhiệt độ tốt nhất so với ngưỡng nhiệt độ đặt. Hệ thống có độ quá điều chỉnh nhỏ, nhanh đáp ứng tới các ngưỡng đặt và giữ ổn định với sai lệch nhiệt độ khi đạt ngưỡng yêu cầu trong khoảng ±10C. Ngoài ra, bộ điều khiển còn có thể hoạt động theo nhiều chế độ khác nhau, bao gồm hoạt động theo chế độ đặt nhiệt độ trực tiếp, hoạt động theo chu trình đặt trước, và chuyển chế độ hoàn toàn tự động.

The Humanoid Walking Robot (HWR) is a research platform for the study of legged and wearable robots actuated with Hydro Muscles. The fluid operated HWR is representative of a class of biologically inspired, and in some aspects highly biomimetic robotic musculoskeletal appendages showing certain advantages in comparison to more conventional artificial limbs and braces for physical therapy/rehabilitation, assistance of daily living, and augmentation. The HWR closely mimics the human body structure and function, including the skeleton, ligaments, tendons, and muscles. The HWR can emulate close to human-like movements even when subjected to simplified control laws. One of the main drawbacks of this approach is the inaccessibility of an appropriate fluid flow management support system, in the form of affordable, lightweight, compact, and good quality valves suitable for robotics applications. To resolve this shortcoming, the Compact Robotic Flow Control Valve (CRFC Valve) is introduced and successfully proof-of-concept tested. The HWR added with the CRFC Valve has potential to be a highly energy efficient, lightweight, controllable, affordable, and customizable solution that can resolve single muscle action.

Robot assisted therapy is becoming increasingly popular. Research has proven it can be of benefit to persons dealing with a variety of disorders, such as Autism Spectrum Disorder (ASD), Attention Deficit Hyperactivity Disorder (ADHD), and it can also provide a source of emotional support e.g. to persons living in seniors’ residences. The advancement in technology and a decrease in cost of products related to consumer electronics, computing and communication has enabled the development of more advanced social robots at a lower cost. This brings us closer to developing such tools at a price that makes them affordable to lower income individuals and families. Currently, in several cases, intensive treatment for patients with certain disorders (to the level of becoming effective) is practically not possible through the public health system due to resource limitations and a large existing backlog. Pursuing treatment through the private sector is expensive and unattainable for those with a lower income, placing them at a disadvantage. Design and effective integration of technology, such as using social robots in treatment, reduces the cost considerably, potentially making it financially accessible to lower income individuals and families in need. The Objective of the research reported in this manuscript is to design and implement a social robot that meets the low-cost criteria, while also containing the required functions to support children with ASD. The design considered contains knowledge acquired in the past through research involving the use of various types of technology for the treatment of mental and/or emotional disabilities.

The growing demand in the industry towards sustainability and the globalization of manufacturing lead to an industrial climate of constant development and improvements, and automotive interior design is not excluded. In 2017 the European Union declared that the material used to generate the bright chrome surfaces of car interiors (CR VI) is toxic and carcinogenic. This implies that Volvo will ban the use of Chrome VI for decorative parts from September 2024.  Finding a more eco-friendly alternative to replace CR VI not only functionally but also in terms of perceived quality and user experience will be an urgent and decisive action.  In this project, the parameters of gloss, haze, color temperature, and metallic depth are investigated in order to figure out which elements ensure the perceived quality of chrome surfaces.  For this purpose, a user study based on different sensory tests and soft metrology was carried out with 48 people, as well as seven samples, five of them more eco-friendly alternatives. This project aims to introduce a set of tools to assess and guarantee the perception of quality by supporting the development of "chrome-look" surfaces in the automotive interior with new sustainable materials. Through this study, correlating soft and hard metrology, it is observed what makes a surface perceived as "high-quality" and which of the more eco-friendly alternatives could be the most optimal to replace Chrome VI in Volvo's car interiors.

Permanent magnets play a key role as a component in a wide range of devices utilised by many industries; they are widely used in several electromechanical applications to convert energy, including actuators, motors and sensors, home appliances, office automation equipment, speakers, aerospace, wind generators and more. Traditionally the adopted PMs were obtained from Rare Earth components, such as NdFeB, with high magnetic performance, but expensive. The research of alternative permanent magnets, in many cases has brought to choose the ferrites, mainly due to their low cost, but sometimes with significant design modifications of the final circuit, and possible increment of the weight. Permanent magnets can roughly be divided into two categories: sintered (metallic) and bonded, these last representing a valid alternative to the first. Bonded magnets consist of two components: a hard magnetic powder and a non-magnetic binder; the powder may be hard ferrite, NdFeB, SmCo, and is mixed with binders for compression or injection moulding. The benefits lie in the adoption of polymeric binders to prepare the magnetic mixture: the resulting magnetic characteristic can be then “tuned” by adopting different percentages of the plastic binder. Moreover, the realisation process is simpler and cheaper than that of sintered materials, and no special protective treatment is needed. The majority of the magnetic circuits are made with soft magnetic materials. Commonly laminated steels are adopted but recently the use of Soft Magnetic Composite (SMC) materials has increased representing a new solution to design the electrical machines with respect to traditional electrical steels. SMC materials are realized with pure Iron grains coated and insulated by means of a layer that should be organic or inorganic. With respect to traditional laminated steel, these materials present different advantages: the capability to lead the magnetic flux in all directions, the volume reduction, the possibility to realize components with new complex shapes and geometries, and the reduction of iron losses, mainly the eddy currents, at medium and high frequency. On the other hand, the mechanical performances, in terms of strength, are in general weak. Furthermore, a new material typology is introduced: the Hybrid Magnetic Composites (HMC), which are obtained with a combination of soft and hard magnetic materials mixed with a binder. The basic idea is that such materials should reflect the performance of AlNiCo magnets, low coercivity and adequate remanence, typically used in sensors applications. Prototypes of traditional and unconventional rotating machines, such as assisted reluctance motors, brushless DC motors, axial flux machines and electromechanical frequency converters, have been studied in own laboratories and tested to evaluate the results coming from the adoption of the proposed materials in substitution of the commonly adopted (and expensive) Rare Earth sintered magnets. Different type of electrical machines can adopt innovative magnetic materials with the aim to improve their performance. Induction motors are very useful and robust machines; on the other hand, such type of machines does not have a high dynamic behaviour. The DC motors can be easily controlled, but the presence of the brushes causes limitations on the efficiency, thermal restrictions and reduced life. The axial flux motors (AFM) have high efficiencies but the construction of the machines is very complex. The synchronous reluctance machines (SRM) have a lower cost compared to brushless ones. In general, the reluctance electrical machines don’t use permanent magnets. In this way, they have a reduction in the costs and allow a high overload capability. On the other hand, the lower power factor and power density, compared to PM synchronous motor (PMSM), are the main disadvantages. The filling of flux barriers with the permanent magnets allows the overcoming of these drawbacks. However, the regular ferrite and NdFeB sintered magnets cannot fill the flux barriers with complex geometries. For this reason, the use of bonded magnets can be a solution for a better utilization and design of flux barriers. Therefore different prototypes have been prepared and analyzed in our laboratories using SMC materials. Several experiments have been performed using dedicated test benches, where magnetic, energetic and mechanical aspects have been considered. On the other hand, with regard to HMCs, various magnets have been made in our laboratories, and different properties have been investigated: the effect of Iron content in the material and, also the binder content effect has been analysed.

As the major electricity consumer, electrical machines play a key role for global energy savings. Machine manufacturers put considerable efforts into the development of more efficient electrical machines for loss reduction and higher power density achievements. A consolidated knowledge of the occurring losses in electrical machines is a basic requirement for efficiency improvements. This thesis deals with iron losses in electrical machines. The major focus is on the influences of the stator core magnetic material due to the machine manufacturing process, temperature influences, and the impact of inverter operation. The first part of the thesis gives an overview of typical losses in electrical machines, with focus put on iron losses. Typical models for predicting iron losses in magnetic materials are presented in a comprehensive literature study. A broad comparison of magnetic materials and the introduction of a new material selection tool conclude this part. Next to the typically used silicon-iron lamination alloys for electrical machines, this thesis investigates also cobalt-iron and nickel-iron lamination sheets. These materials have superior magnetic properties in terms of saturation magnetization and hysteresis losses compared to silicon-iron alloys. The second and major part of the thesis introduces the developed measurement system of this project and presents experimental iron loss investigations. Influences due to machine manufacturing changes are studied, including punching, stacking and welding effects. Furthermore, the effect of pulse-width modulation schemes on the iron losses and machine performance is examined experimentally and with finite-element method simulations. For nickel-iron lamination sheets, a special focus is put on the temperature dependency, since the magnetic characteristics and iron losses change considerably with increasing temperature. Furthermore, thermal stress-relief processes (annealing) are examined for cobalt-iron and nickel-iron alloys by magnetic measurements and microscopic analysis. A thermal method for local iron loss measurements is presented in the last part of the thesis, together with experimental validation on an outer-rotor permanent magnet synchronous machine.

QC 20140516

The hands and feet account for half of the complexity of the musculoskeletal system, while the skin of the hand is specialised with many important structures. Much of the subtlety of the mechanism of the hand lies in the soft tissues, and the tactile and proprioceptive sensitivity depends on the large number of mechanoreceptors embedded in specific structures of the soft tissues. This thesis investigates synthetic materials and manufacturing techniques to enable building robots that reproduce the biomechanics and tactile sensitivity of vertebrates – histomimetic robotics. The material and mechanical anatomy of the hand is reviewed, highlighting difficulty of numerical measurement in soft-tissue anatomy, and the predictive nature of descriptive anatomical knowledge. The biomechanical mechanisms of the hand and their support of sensorimotor control are presented. A palate of materials and layup techniques are identified for emulating ligaments, joint surfaces, tendon networks, sheaths, soft matrices, and dermal structures. A method for thermoplastically drawing fine elastic fibres, with liquid metal amalgam cores, for connecting embedded sensors is demonstrated. The performance requirements of skeletal muscles are identified. Two classes of muscle-like bulk MEMS electrostatic actuators are shown theoretically to be capable of meeting these requirements. Means to manufacture them, and their additional application as mechanoreceptors are described. A novel machine perception algorithm is outlined as a solution to the problem of measuring soft tissue anatomy, CAD/CAE/CNC for layup of histomimetic robots, and sensory perception by such robots. The results of the work support the view that histomimetic robotics is a viable approach, and identify a number of areas for further investigation including: polymer modification by graft-polymerisation, automated layup tools, and machine perception.

abstract: Soft materials are matters that can easily deform from their original shapes and structures under thermal or mechanical stresses, and they range across various groups of materials including liquids, foams, gels, colloids, polymers, and biological substances. Although soft materials already have numerous applications with each of their unique characteristics, integrating materials to achieve complementary functionalities is still a growing need for designing advanced applications of complex requirements. This dissertation explores a unique approach of utilizing intermolecular interactions to accomplish not only the multifunctionality from combined materials but also their tailored properties designed for specific tasks. In this work, multifunctional soft materials are explored in two particular directions, ionic liquids (ILs)-based mixtures and interpenetrating polymer network (IPN). First, ILs-based mixtures were studied to develop liquid electrolytes for molecular electronic transducers (MET) in planetary exploration. For space missions, it is challenging to operate any liquid electrolytes in an extremely low-temperature environment. By tuning intermolecular interactions, the results demonstrated a facile method that has successfully overcome the thermal and transport barriers of ILs-based mixtures at extremely low temperatures. Incorporation of both aqueous and organic solvents in ILs-based electrolyte systems with varying types of intermolecular interactions are investigated, respectively, to yield optimized material properties supporting not only MET sensors but also other electrochemical devices with iodide/triiodide redox couple targeting low temperatures. Second, an environmentally responsive hydrogel was synthesized via interpenetrating two crosslinked polymer networks. The intermolecular interactions facilitated by such an IPN structure enables not only an upper critical solution temperature (UCST) transition but also a mechanical enhancement of the hydrogel. The incorporation of functional units validates a positive swelling response to visible light and also further improves the mechanical properties. This studied IPN system can serve as a promising route in developing “smart” hydrogels utilizing visible light as a simple, inexpensive, and remotely controllable stimulus. Over two directions across from ILs to polymeric networks, this work demonstrates an effective strategy of utilizing intermolecular interactions to not only develop multifunctional soft materials for advanced applications but also discover new properties beyond their original boundaries.
Dissertation/Thesis
Doctoral Dissertation Chemical Engineering 2020

碩士
中原大學
機械工程學系
88
In this study, the step of packing machines for soft materials which carry packing bag, open packing bag, push the pants type of adult’s diaper in the packing bag, thermal sealing, excision of the process to finish the last step. This study presents a modularize process to design and manufacture such packing machine with desired performances. Using the language of sequential function chart(SFC) in programmable logic controller(PLC) which is step to step and modularize language. The packing machines of soft materials have two key-points. One of the questions is about the success rate of the packing state during opening the packing bag. In this study use different flat to try this work and find the best way to use. The other is thermal sealing and excision. It uses temperature controller to keep the thermal coupler at the same temperature. The contribution of the work is beneficial to the systematic design, and automation of production of packing machine for industry.

Humanoid robots are those resembling their motion and functioning similar to human beings, having capabilities of doing day to day activities similar to man and replace him in every possible way. These activities vary from daily activities such as walking, standing, and bowing, to staircase climbing, running, and kneeling. The current research integrates multiple technologies and methodologies within a system such as 3D printing, Inverse Kinematic programming, Power electronics, Control system, Learning algorithms, Mechanical Design, Human-computer interaction, software tools for collaborative projects. A detailed mechanical design procedure has been carried out in CAD along with its structural analysis in FEA. Followed by Kinematic and Dynamic analysis of the system considering suitable physical properties in V-rep

abstract: Deformable heat exchangers could provide a multitude of previously untapped advantages ranging from adaptable performance via macroscale, dynamic shape change (akin to dilation/constriction seen in blood vessels) to enhanced heat transfer at thermal interfaces through microscale, surface deformations. So far, making deformable, ‘soft heat exchangers’ (SHXs) has been limited by the low thermal conductivity of materials with suitable mechanical properties. The recent introduction of liquid-metal embedded elastomers by Bartlett et al1 has addressed this need. Specifically, by remaining soft and stretchable despite the addition of filler, these thermally conductive composites provide an ideal material for the new class of “soft thermal systems”, which is introduced in this work. Understanding such thermal systems will be a key element in enabling technology that require high levels of stretchability, such as thermoregulatory garments, soft electronics, wearable electronics, and high-powered robotics. Shape change inherent to SHX operation has the potential to violate many conventional assumptions used in HX design and thus requires the development of new theoretical approaches to predict performance. To create a basis for understanding these devices, this work highlights two sequential studies. First, the effects of transitioning to a surface deformable, SHX under steady state static conditions in the setting of a liquid cooling device for thermoregulation, electronics and robotics applications was explored. In this study, a thermomechanical model was built and validated to predict the thermal performance and a system wide analysis to optimize such devices was carried out. Second, from a more fundamental perspective, the effects of SHXs undergoing transient shape deformation during operation was explored. A phase shift phenomenon in cooling performance dependent on stretch rate, stretch extent and thermal diffusivity was discovered and explained. With the use of a time scale analysis, the extent of quasi-static assumption viability in modeling such systems was quantified and multiple shape modulation regime limits were defined. Finally, nuance considerations and future work of using liquid metal-silicone composites in SHXs were discussed.
Dissertation/Thesis
Doctoral Dissertation Engineering 2020

碩士
國立臺北科技大學
機電整合研究所
99
The purpose of this study is to design a flexible robot gripper that can catch a variety of items irregular shapes, which are mostly seen in the skill competition game. If a stable flexible robot gripper is successfully developed, it can be further used in industry. First, the literature studied vacuum, magnetic-type robot grippers and found that flexible robot grippers haven’t been deeply studied by anyone. Then we do a theoretical analysis, and make use of the theory of cantilever mechanics and the analysis of the holding force of the gripper so that the relationship between the structure of the flexible robot gripper and the holding force can be obtained. Then we process a series of tests of holding power of the flexible robot gripper. Comparing the tests by using a suspended system, it is found that the best design of the structure is to install 24 fingers with a length of 165 millimeter and a diameter of 0.4 millimeter. This design is the best choice for the gripper to catch items with the least work. The research result shows that the flexible robot gripper can catch items ranging from a diameter of 20 to 100 millimeter when it open and that an item of 3 kilogram can be taken by the gripper when the voltage is 6V.

The research work carried out during my PhD course has been focused on the following two main topics: 1) The design, synthesis and characterization of new nature-inspired organic electroluminescent emitters and their application in opto-electronic devices. This work will be discussed in the SECTION 1. 2) The design, synthesis and properties of eumelanin-based semiconductors and their applications in electronic devices. This work will be discussed in the SECTION 2. The research activity discussed in SECTION 1 will concern the design, the synthesis and the characterization of new nature-inspired organic electroluminescent emitters and their applications in opto-electronic devices. In details, the following points will be stressed: - the identification of suitable nature-inspired heterocyclic platforms that can be used to develop new electroluminescent materials for opto-electronic applications; - the design of structural modifications of natural compounds for a better match with organic electronics requirements by exploiting the theoretical approach; - the development of new rapid and convenient synthetic strategies for a gram scale production of the organic emitters; - the structural, photo-physical, electronic and thermal characterization of the synthesized compounds along with the investigation of the performances of the opto-electronic devices thereof. The research activity described in SECTION 2 has been devoted to the design, synthesis, processing and properties of eumelanin-based semiconductors and their applications in electronic devices, with the aim of throwing new light onto this controversial issue. In details, the following points will be stressed: - the identification of suitable approaches for a more easy processing of melanin thin films; - the investigation of the factors influencing the conductivity of melanin thin films; - the study of the possible role of melanin thin films as innovative bio-interface.

Ionic polymer metal composite (IPMC) is used in various bio-inspired systems, such as fish and tadpole-like robots swimming in water. The deflection of this smart material results from several internal and external factors, such as water distribution and surface conductivity. IPMC strips with a variety of water concentration on the surfaces and surface conductivity show various deflection patterns. Even without any external excitation, the strips can bend due to non-uniform water distribution. On the other hand, in order to understand the effects of surface conductivity in an aquatic environment, an IPMC strip with two wires connected to two distinct spots was used to demonstrate the power loss due to the surface resistance. Three types of input signals, sawtooth, sinusoidal, and square waves, were used to compare the difference between the input and output signals measured at the two spots. Thick (1-mm) IPMC strips were fabricated and employed in this research to sustain and drive the robot with sufficient forces. Furthermore, in order to predict and control the deflection, researchers developed the appropriate mathematical models. The special working principle, related to internal mobile cations with water molecules, however, makes the system complicated to be modeled and simulated. An IPMC strip can be modeled as a cantilever beam with loading distribution on the surface. Nevertheless, the loading distribution is non-uniform due to the non-perfect surface metallic plating, and four different kinds of imaginary loading distribution are employed in this model. On the other hand, a reverse-predicted method is used to find out the transfer function of the IPMC system according to the measured deflection and the corresponding input voltage. Several system-identification structures, such as autoregressive moving average with exogenous (ARX/ARMAX), output-error (OE), Box-Jenkins (BJ), and prediction-error minimization (PEM) models, are used to model the system with their specific mathematic principles. Finally, a novel linear time-variant (LTV) concept and method is introduced and applied to simulate an IPMC system. This kind of model is different from the previous linear time-invariant (LTI) models because the IPMC internal environment may be unsteady, such as free cations with water molecules. This phenomenon causes the variation of each internal part. In addition, the relationship between the thickness of IPMC strips and the deflection can be obtained by this concept. Finally, based on the experimental results above, an aquatic walking robot (102 mm × 80 mm × 43 mm, 39 g) with six 2-degree-of-freedom (2-DOF) legs has been designed and implemented. It walked in water at the speed of 0.5 mm/s. The average power consumption is 8 W per leg. Each leg has a thigh and a shank to generate 2-DOF motions. Each set of three legs walked together as a tripod to maintain the stability in operation.

碩士
龍華科技大學
電機工程系碩士班
107
The present study established a six-degrees-of-freedom (6-DOF) robotic arm equipped with binocular vision and an adaptive gripper. The arm can be employed to sort and stack products in the modern manufacturing industry. Regarding the machine configuration, in response to the Industry 4.0 demands for low quantity, great variety, and flexible machining, the humanoid robotic arm established in this study has a merchant binocular vision system, a self-developed adaptive gripper that can grip items of different shapes, and a 6-DOF humanoid robotic arm developed in the laboratory. With respect to system analysis, the DH method was employed to establish forward and inverse kinematic models of the arm joints and end points. The scientific computing software MATLAB was used to verify the forward and inverse kinematics and simulate the working space of the robotic arm. For system control, industrial PCs and ethernet for control automation technology are employed. The visual programming software LabVIEW was used to develop image recognition and motor controlling programs for achieving integrated control of the binocular vision and 6-DOF robotic arm. In addition to meeting the low-quantity and great-variety demands of flexible manufacture in Industry 4.0, the system established in this study resolves the problems of complex cable configurations and the lack of depth perception of conventional robotic arms due to their monocular vision. The experiment results revealed that the 6-DOF automatic sorting robotic arm is capable of identifying the coordinates of objects using its binocular vision system and can automatically complete sorting and stacking tasks according to the shape of each object by using the robotic arm and adaptive gripper.

Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia
Atualmente, os robôs operam em diversos tipos de indústria, serviços médicos e até mesmo em aplicações de lazer. Os robôs têm melhorado as suas características ao nível da velocidade, precisão e capacidade de repetição de tarefas. Contudo, os mecanismos robóticos tradicionais são normalmente constituídos por materiais rígidos, apresentando dificuldades de deformação e adaptação, principalmente no manuseamento de objetos frágeis e/ou complexos, assim como em aplicações onde o ambiente não é perfeitamente conhecido. Estas aplicações requerem um comportamento robótico complacente, tanto ao nível de software como de hardware. Assim, surge uma nova subárea da robótica, chamada soft robotics. Baseando-se em estruturas biológicas, esta assenta no desenvolvimento de componentes robóticos com materiais elásticos, flexíveis e de baixa rigidez (materiais suaves). Esta subárea comprovou apresentar potencial significativo na fabricação de grippers e manipuladores. A possibilidade de fabricar estruturas de materiais suaves, permite criar formas realísticas, diminuir o peso, lidar com um vasto número de objetos e aumentar a segurança dos equipamentos. Neste âmbito, esta dissertação apresenta o design e o processo de fabricação de um protótipo de uma mão robótica, atuada pneumaticamente, concebida com materiais suaves, parcialmente fabricados pelo processo de impressão 3D. Este conceito permite o desenvolvimento de uma mão robótica a um custo relativamente reduzido, com forma anatómica e reduzida complexidade de controlo. O estudo do comportamento dos materiais elásticos é também estudado nesta dissertação. É proposto um modelo numérico, utilizado na Análise de Elementos Finitos (FEA) para simular o comportamento da mão quando esta está atuada. Os resultados das simulações são comparados com testes experimentais, comprovando assim parcialmente a viabilidade do modelo numérico.
Nowadays, robots are used in a wide range of applications such as industrial manufacturing, medical services and even in leisure applications. Robots have substantially increased their capabilities in terms of speed, precision and task execution abilities. However, they are commonly made of rigid materials, presenting limitations in terms of deformation and adaptation when handling fragile and/or complex objects, especially when the environment is not entirely known. These applications require a complacent robot behaviour both at software and hardware level. In order to deal with such a requirement, a new robotics subarea, called soft robotics, arises. This new subarea is based on biological structures and allows a designer to create robot components, with elastic, flexible and low rigidity materials (soft materials). Soft robotics has proven its potential in the manufacture of grippers and manipulators. Soft materials provide the ability to create realistic shapes, reduced weight and increase the safety of the equipment. In this context, this dissertation presents the design and manufacture of a pneumatic robotic hand prototype made of soft materials, and partially fabricated by 3D printing. This concept allows the design and fabrication of an anthropomorphic hand at a low cost, with anatomical shape, desired compliance and reduced control complexity (since the number of actuated degrees-of-freedom is lower than the number of degrees-of-freedom of the robotic hand). There is no systematic procedure or methodology to simulate the behaviour of elastic materials. A numerical model implemented in Finite Element Analysis (FEA) is proposed to simulate the hand behaviour when it is actuated. Simulations results proved the model effectiveness when compared with experimental tests.

The present thesis entitled “Design and Synthesis of Novel Soft Composites from Physical Gels and Nanomaterials” deals with soft materials derived from low molecular weight gels and nanomaterials. Chapter 1 gives a general introduction and overview of the low molecular weight gel (LMOG) which forms the basis of the work. It delves with the history of research in physical gel field, design of different types of gelator molecules, their interesting self-assembly patterns, potential applications of these gelator molecules as well as challenges to design new gelator molecules. It also encompasses the relatively recent area of two component gel system to conveniently bypass the cumbersome synthetic protocol. The aspect of liquid crystallinity in the gel phase is also discussed to throw light on the pattern of assembly and potential uses of these materials. Towards the end there is a comprehensive discussion on the smart nanocomposites derived from LMOGs and nanomaterials. The design, synthesis and numerous applications of inorganic-organic hybrid composites are discussed. Chapter 2A describes the synthesis and characterization of a variety of fatty acid amides of different naturally occurring L-amino acids whose molecular structures are shown in Chart 2A.1. Some of them were found to form gels with various hydrocarbons. The gelation properties of these compounds were studied by a number of physical methods including FT-IR spectroscopy, X-ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry, rheology and it was found that gelation was critically dependent on the fatty acid chain length and nature of the amino acid. Among them, L-alanine based gelators were found to be the most efficient and versatile as they self-assemble into a layered structure to form the gel network. Mechanisms for the assembly and formation of gels from these molecules are discussed. (Structural formula) Chart 2A.1. Molecular structures of various fatty acid amides of different amino acids. Chapter 2B describes efficient gelation of both aliphatic and aromatic hydrocarbon solvents by a fatty acid amide, n-lauroyl-L-alanine (Chapter 2B.1). In addition, this compound was found to gelate the binary solvent mixtures comprised of aromatic hydrocarbon e.g. toluene and aliphatic hydrocarbon e.g. n-heptane. SEM and AFM showed that the fiber thickness of the gel assembly increases progressively in the binary mixture of n-heptane and toluene with increasing percentage of toluene. The self- Chart 2B.1. Molecular structure of the gelator. assembly patterns of the gels in individual solvents, n-heptane and toluene are however, different. The toluene gel consists of predominantly one type of morphological species while n-heptane gel has more than one species leading to polymorphic nature of the gel. The n-heptane gel is thermally more stable than the toluene gel as evident from the measurement using differential scanning calorimetry. The thermal stability of the gels prepared in the binary mixture of n-heptane and toluene is dependent on the composition of solvent mixture. Rheology of the gels shows that they are shear-thinning material and show characteristic behavior of soft viscoelastic solids. For the gels prepared from binary solvent mixture of toluene and n-heptane, with incorporation of more toluene in the binary mixture, the gel becomes a more viscoelastic solid. The time sweep rheology experiment demonstrates that the gel made in n-heptane has faster gel formation kinetics than that prepared in toluene. Chapter 2C describes lyotropic mesophase formation by organogels of different fatty acid amides of L-alanine in aromatic solvents. The helical assembly, characteristic of the cholesteric mesophase was found to exhibit reflection bands in circular dichroism spectra. The reflection bands corresponded to the pitch of the helical arrangement of the gelator molecules in the aromatic solvent. Transmission Electron Microscopy (TEM) showed presence of twist in the gel fibres. Polarising optical microscopy of the organogel exhibited weak birefringence confirming lyotropic nature of the assembly. Chapter 3 deals with synthesis and characterization of a new class of molecules with molecular structures shown in Chart 3.1. Among a variety of amino acid based molecules only alanine and serine based molecules were found to form translucent gels in aliphatic hydrocarbons such as n-heptane. TEM showed presence of fiber like structures for alanine whereas serine based gelator produces unique network like structures. SEM of the dried gels exhibited presence of three dimensional fibrous networks to spongy globular cauliflower like structures depending on the molecular structure of the gelators. Rheological studies of the organogels showed that they behave like typical LMOG gels. The oscillatory rheological studies demonstrated that the L-serine based gelator, 5 formed more viscoelastic solid like gel than that of L-alanine based gelator, 1 in n-heptane. Chart 3.1. Molecular structures of different amino acid derivatives from 3,4,5-tri-dodecyloxybenzoic acid scaffold. Chapter 4A presents design and properties of new nanocomposites from LMOG and metal nanoparticles (Chart 4A.1). The profound influence of nanoparticle (NP) incorporation into physical gels was evident from various microscopic and bulk properties. The interaction of nanoparticles with the gelator assembly was found to depend critically on the capping agent coating the nanoparticles. TEM showed long range Chart 4A.1. Molecular structures of the gelator and various AuNPs synthesized. directional assembly of the certain AuNPs along the gel fibers. SEM of the dried gels and nanocomposites indicated that the morphological transformation in the composite microstructures depended profoundly on the capping agent of the nanoparticle. Differential Scanning Calorimetry showed that gel formation from sol postponed to lower temperature with incorporation of AuNPs having capping agents which were able to interact with the gel fibers. Rheological studies indicated that the gel-nanoparticle composites exhibit greater rigidity as compared to the naked gel only when the capping agents were able to interdigitate into the gelator assembly. Also, very low percentage of the AuNPs incorporation could switch the cholesteric mesophase of gel assembly, as evident from circular dichroism. We have been able to define a relationship between materials and molecular properties via manipulation of the molecular structures of NP capping agents. Chapter 4B discusses the design and preparation of novel organogel-carbon nanotube composites by incorporation of single-walled carbon nanotubes (SWNT) into physical gels formed by an L-alanine based Low Molecular Mass Organogelator (Chart 4B.1). The gelation process and the properties of the resulting nanocomposites were found to depend on the kind of SWNTs incorporated in the gels. With pristine SWNTs, only a limited amount could be dispersed in the organogels. Attempted incorporation of higher amounts of pristine SWNTs led to precipitation from the gel. To improve their solubility in the gel matrix, a variety of SWNTs functionalized with different aliphatic and aromatic chains were synthesized (Chart 4B.1). Scanning electron microscope images of the nanocomposites showed that the texture and organization of the gel aggregates were altered upon incorporation of SWNTs. The microstructures of nanocomposites were found to depend on the kind of SWNTs used. Incorporation of functionalized SWNTs into the organogels depressed the sol to gel transition temperature, with the n-hexadecyl chain functionalized SWNTs being more effective than the n-dodecyl chain functionalized counterpart. Rheological investigations of pristine SWNT containing gels indicated that the flow of nanocomposites became resistant to applied stress at a very low wt-% of SWNT incorporation. Again, more effective control of flow behavior was achieved with functionalized SWNTs possessing longer hydrocarbon chains. This happens presumably via effective interdigitation of the pendant chains with the fatty acid amides of L-alanine in the gel assembly. Also, the helical cholesteric mesophase formed by the toluene gel could be switched to a layer stacked assembly by doping functional SWNT. Remarkably, by using a near IR laser irradiation at 1064 nm for a short duration (1 min) at room temperature, it was possible to selectively induce a gel-to-sol phase transition of the nanocomposites, while prolonged irradiation (30 min) of the organogel under identical conditions did not cause gel melting. Chart 4B.1. Molecular structures of the gelator and different functionalized SWNT synthesized. Chapter 5A presents design of two component hydrogels and their potential utilization as a template for metal nanoparticle synthesis. Among a variety of acids and amines (Chart 5A.1) only stearic acid or eicosanoic acid when mixed with di- or oligomeric amines in specific molar ratios form stable gels in water. The formation of such hydrogels depends on the hydrophobicity of the fatty acid, and also on the type of amine used. The gelation properties of these two component systems were investigated using electron microscopy, FTIR, 1H NMR spectroscopy, differential scanning calorimetry (DSC) and both single crystal and cast film X-ray diffraction. FTIR spectral analysis suggests salt formation during gelation. 1H NMR of the gels indicates that the fatty acid chains are immobilized in the gel state and when the gel is melted, these chains regain their mobility. Analysis of DSC data indicates that increase in spacer length in the di-/oligomeric amine lowers the gel melting temperature. Two of these gelator salts developed into crystals and structural details of such systems could be secured by single-crystal X-ray diffraction analysis. The structural information of the salts thus obtained was compared with the XRD data of the self-supporting films of those gels. Such analyses provided pertinent structural insight on the supramolecular interactions that prevail within these gelator assemblies. From the crystal structure it is confirmed that the multilayered lamellar aggregates exist in the gel and it also showed that only one plane of symmetry is present in the gel state. Finally, the hydrogel was used as a medium for the synthesis of silver nanoparticles. The nanoparticles were found to position themselves on the fibers and produce a long ordered assembly of gel-nanoparticle composite (Figure 5A.1). Chart 5A.1. Structures and abbreviations of different acids and amines checked for gelation. Figure 5A.1. TEM images of gel-Ag-NP composite. (a) Ag-NP synthesized in hydrogel of SA-IBPA (1:3.5), (b) Magnified images of Ag-NP preferentially residing on gel fibers. Chapter 5B demonstrates the aptitude of supramolecular hydrogel formation using simple bile acids e.g. lithocholic acid (LCA) in aqueous solution containing di- or oligomeric amines (Chart 5B.1). By variation of the choice of the amines in such mixture the hydrogelation properties could be modulated. However, replacement of LCA by cholic acid or deoxycholic acid resulted in no hydrogelation. FT-IR studies show that the carboxylate and ammonium residues of the two components are primarily involved in salt formation. This promotes further assembly of the components reinforced by continuous Chart 5B.1. Structures and abbreviations of different bile acids and amines checked for gelation. hydrogen bonded network leading to gelation. Electron microscopy shows that the morphology of the gels of two component systems which also depends strongly on the amine part. Variation of amine component from the simple ethanediamine (EDA) to oligomeric amine with lithocholic acid changes the morphology of the assembly from long one dimensional nanotubes to three dimensional complex structures. Single crystal X-ray diffraction analysis with one of the amine-LCA complexes suggested the motif of fiber formation where the amines participate with the carboxylate and hydroxyl moiety through H-bonding and electrostatic forces. The rheological properties of this class of two component system provide clear evidence that this system is a shear-sensitive hydrogel and the flow behavior can be modulated varying the acid-amine ratio. From small angle neutron scattering study, it becomes clear that loose gel from LCA-EDA shows scattering oscillation due to the presence of non interacting nanotubules while for gels of LCA with oligomeric amine the individual fibers come together to form complex three dimensional structures of higher length scale.(For structural formula pl refer the pdf file)

The present thesis entitled “Design and Synthesis of Novel Soft Composites from Physical Gels and Nanomaterials” deals with soft materials derived from low molecular weight gels and nanomaterials. Chapter 1 gives a general introduction and overview of the low molecular weight gel (LMOG) which forms the basis of the work. It delves with the history of research in physical gel field, design of different types of gelator molecules, their interesting self-assembly patterns, potential applications of these gelator molecules as well as challenges to design new gelator molecules. It also encompasses the relatively recent area of two component gel system to conveniently bypass the cumbersome synthetic protocol. The aspect of liquid crystallinity in the gel phase is also discussed to throw light on the pattern of assembly and potential uses of these materials. Towards the end there is a comprehensive discussion on the smart nanocomposites derived from LMOGs and nanomaterials. The design, synthesis and numerous applications of inorganic-organic hybrid composites are discussed. Chapter 2A describes the synthesis and characterization of a variety of fatty acid amides of different naturally occurring L-amino acids whose molecular structures are shown in Chart 2A.1. Some of them were found to form gels with various hydrocarbons. The gelation properties of these compounds were studied by a number of physical methods including FT-IR spectroscopy, X-ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry, rheology and it was found that gelation was critically dependent on the fatty acid chain length and nature of the amino acid. Among them, L-alanine based gelators were found to be the most efficient and versatile as they self-assemble into a layered structure to form the gel network. Mechanisms for the assembly and formation of gels from these molecules are discussed. (Structural formula) Chart 2A.1. Molecular structures of various fatty acid amides of different amino acids. Chapter 2B describes efficient gelation of both aliphatic and aromatic hydrocarbon solvents by a fatty acid amide, n-lauroyl-L-alanine (Chapter 2B.1). In addition, this compound was found to gelate the binary solvent mixtures comprised of aromatic hydrocarbon e.g. toluene and aliphatic hydrocarbon e.g. n-heptane. SEM and AFM showed that the fiber thickness of the gel assembly increases progressively in the binary mixture of n-heptane and toluene with increasing percentage of toluene. The self- Chart 2B.1. Molecular structure of the gelator. assembly patterns of the gels in individual solvents, n-heptane and toluene are however, different. The toluene gel consists of predominantly one type of morphological species while n-heptane gel has more than one species leading to polymorphic nature of the gel. The n-heptane gel is thermally more stable than the toluene gel as evident from the measurement using differential scanning calorimetry. The thermal stability of the gels prepared in the binary mixture of n-heptane and toluene is dependent on the composition of solvent mixture. Rheology of the gels shows that they are shear-thinning material and show characteristic behavior of soft viscoelastic solids. For the gels prepared from binary solvent mixture of toluene and n-heptane, with incorporation of more toluene in the binary mixture, the gel becomes a more viscoelastic solid. The time sweep rheology experiment demonstrates that the gel made in n-heptane has faster gel formation kinetics than that prepared in toluene. Chapter 2C describes lyotropic mesophase formation by organogels of different fatty acid amides of L-alanine in aromatic solvents. The helical assembly, characteristic of the cholesteric mesophase was found to exhibit reflection bands in circular dichroism spectra. The reflection bands corresponded to the pitch of the helical arrangement of the gelator molecules in the aromatic solvent. Transmission Electron Microscopy (TEM) showed presence of twist in the gel fibres. Polarising optical microscopy of the organogel exhibited weak birefringence confirming lyotropic nature of the assembly. Chapter 3 deals with synthesis and characterization of a new class of molecules with molecular structures shown in Chart 3.1. Among a variety of amino acid based molecules only alanine and serine based molecules were found to form translucent gels in aliphatic hydrocarbons such as n-heptane. TEM showed presence of fiber like structures for alanine whereas serine based gelator produces unique network like structures. SEM of the dried gels exhibited presence of three dimensional fibrous networks to spongy globular cauliflower like structures depending on the molecular structure of the gelators. Rheological studies of the organogels showed that they behave like typical LMOG gels. The oscillatory rheological studies demonstrated that the L-serine based gelator, 5 formed more viscoelastic solid like gel than that of L-alanine based gelator, 1 in n-heptane. Chart 3.1. Molecular structures of different amino acid derivatives from 3,4,5-tri-dodecyloxybenzoic acid scaffold. Chapter 4A presents design and properties of new nanocomposites from LMOG and metal nanoparticles (Chart 4A.1). The profound influence of nanoparticle (NP) incorporation into physical gels was evident from various microscopic and bulk properties. The interaction of nanoparticles with the gelator assembly was found to depend critically on the capping agent coating the nanoparticles. TEM showed long range Chart 4A.1. Molecular structures of the gelator and various AuNPs synthesized. directional assembly of the certain AuNPs along the gel fibers. SEM of the dried gels and nanocomposites indicated that the morphological transformation in the composite microstructures depended profoundly on the capping agent of the nanoparticle. Differential Scanning Calorimetry showed that gel formation from sol postponed to lower temperature with incorporation of AuNPs having capping agents which were able to interact with the gel fibers. Rheological studies indicated that the gel-nanoparticle composites exhibit greater rigidity as compared to the naked gel only when the capping agents were able to interdigitate into the gelator assembly. Also, very low percentage of the AuNPs incorporation could switch the cholesteric mesophase of gel assembly, as evident from circular dichroism. We have been able to define a relationship between materials and molecular properties via manipulation of the molecular structures of NP capping agents. Chapter 4B discusses the design and preparation of novel organogel-carbon nanotube composites by incorporation of single-walled carbon nanotubes (SWNT) into physical gels formed by an L-alanine based Low Molecular Mass Organogelator (Chart 4B.1). The gelation process and the properties of the resulting nanocomposites were found to depend on the kind of SWNTs incorporated in the gels. With pristine SWNTs, only a limited amount could be dispersed in the organogels. Attempted incorporation of higher amounts of pristine SWNTs led to precipitation from the gel. To improve their solubility in the gel matrix, a variety of SWNTs functionalized with different aliphatic and aromatic chains were synthesized (Chart 4B.1). Scanning electron microscope images of the nanocomposites showed that the texture and organization of the gel aggregates were altered upon incorporation of SWNTs. The microstructures of nanocomposites were found to depend on the kind of SWNTs used. Incorporation of functionalized SWNTs into the organogels depressed the sol to gel transition temperature, with the n-hexadecyl chain functionalized SWNTs being more effective than the n-dodecyl chain functionalized counterpart. Rheological investigations of pristine SWNT containing gels indicated that the flow of nanocomposites became resistant to applied stress at a very low wt-% of SWNT incorporation. Again, more effective control of flow behavior was achieved with functionalized SWNTs possessing longer hydrocarbon chains. This happens presumably via effective interdigitation of the pendant chains with the fatty acid amides of L-alanine in the gel assembly. Also, the helical cholesteric mesophase formed by the toluene gel could be switched to a layer stacked assembly by doping functional SWNT. Remarkably, by using a near IR laser irradiation at 1064 nm for a short duration (1 min) at room temperature, it was possible to selectively induce a gel-to-sol phase transition of the nanocomposites, while prolonged irradiation (30 min) of the organogel under identical conditions did not cause gel melting. Chart 4B.1. Molecular structures of the gelator and different functionalized SWNT synthesized. Chapter 5A presents design of two component hydrogels and their potential utilization as a template for metal nanoparticle synthesis. Among a variety of acids and amines (Chart 5A.1) only stearic acid or eicosanoic acid when mixed with di- or oligomeric amines in specific molar ratios form stable gels in water. The formation of such hydrogels depends on the hydrophobicity of the fatty acid, and also on the type of amine used. The gelation properties of these two component systems were investigated using electron microscopy, FTIR, 1H NMR spectroscopy, differential scanning calorimetry (DSC) and both single crystal and cast film X-ray diffraction. FTIR spectral analysis suggests salt formation during gelation. 1H NMR of the gels indicates that the fatty acid chains are immobilized in the gel state and when the gel is melted, these chains regain their mobility. Analysis of DSC data indicates that increase in spacer length in the di-/oligomeric amine lowers the gel melting temperature. Two of these gelator salts developed into crystals and structural details of such systems could be secured by single-crystal X-ray diffraction analysis. The structural information of the salts thus obtained was compared with the XRD data of the self-supporting films of those gels. Such analyses provided pertinent structural insight on the supramolecular interactions that prevail within these gelator assemblies. From the crystal structure it is confirmed that the multilayered lamellar aggregates exist in the gel and it also showed that only one plane of symmetry is present in the gel state. Finally, the hydrogel was used as a medium for the synthesis of silver nanoparticles. The nanoparticles were found to position themselves on the fibers and produce a long ordered assembly of gel-nanoparticle composite (Figure 5A.1). Chart 5A.1. Structures and abbreviations of different acids and amines checked for gelation. Figure 5A.1. TEM images of gel-Ag-NP composite. (a) Ag-NP synthesized in hydrogel of SA-IBPA (1:3.5), (b) Magnified images of Ag-NP preferentially residing on gel fibers. Chapter 5B demonstrates the aptitude of supramolecular hydrogel formation using simple bile acids e.g. lithocholic acid (LCA) in aqueous solution containing di- or oligomeric amines (Chart 5B.1). By variation of the choice of the amines in such mixture the hydrogelation properties could be modulated. However, replacement of LCA by cholic acid or deoxycholic acid resulted in no hydrogelation. FT-IR studies show that the carboxylate and ammonium residues of the two components are primarily involved in salt formation. This promotes further assembly of the components reinforced by continuous Chart 5B.1. Structures and abbreviations of different bile acids and amines checked for gelation. hydrogen bonded network leading to gelation. Electron microscopy shows that the morphology of the gels of two component systems which also depends strongly on the amine part. Variation of amine component from the simple ethanediamine (EDA) to oligomeric amine with lithocholic acid changes the morphology of the assembly from long one dimensional nanotubes to three dimensional complex structures. Single crystal X-ray diffraction analysis with one of the amine-LCA complexes suggested the motif of fiber formation where the amines participate with the carboxylate and hydroxyl moiety through H-bonding and electrostatic forces. The rheological properties of this class of two component system provide clear evidence that this system is a shear-sensitive hydrogel and the flow behavior can be modulated varying the acid-amine ratio. From small angle neutron scattering study, it becomes clear that loose gel from LCA-EDA shows scattering oscillation due to the presence of non interacting nanotubules while for gels of LCA with oligomeric amine the individual fibers come together to form complex three dimensional structures of higher length scale.(For structural formula pl refer the pdf file)

The thesis entitled “Design, Synthesis and Properties of Novel Oligo-Phenylenevinylene based Supramolecular Photochromic Gels and Soft Composites with Nanomaterials” deals with soft materials derived from low molecular mass photochromic gels and nanomaterials. Chapter 1 gives a general introduction and overview of the low molecular mass gel (LMMG). It briefly delves into the history of research in physical gel field, design of different types of photochromic gelator molecules, their interesting self-assembly patterns, potential applications of these gelator molecules as well as challenges to design of new gelator molecules. A comprehensive discussion on the synthesis and numerous applications of smart nanocomposites derived from LMMGs and nanomaterials were discussed. It also encompasses the relatively recent area of two component gel system to conveniently bypass the cumbersome synthetic protocol. Interesting photophysical properties of these photochromic LMMGs were discussed towards their light-harvesting properties and aggregation induced white-light emission. Chapter 2 describes the synthesis and self-assembly properties of all-trans-tri(p-phenylenevinylene) (TPV) based molecules possessing different terminal groups, e.g. oxime, hydrazone, phenylhydrazone and semicarbazone (Chart 2A.1). Various spectroscopic and microscopic studies show the aggregation pattern of the self-assemblies promoted by hydrogen bonding, aromatic π-stacking and van der Waals interactions among the individual TPV units (Figure 2A.1). The melting temperatures of the gels and viscoelastic behaviour indicate that the presence of more hydrogen-bonding donors in the periphery of the gelator molecules makes the gel thermally and mechanically more robust. However, in the presence of more numbers of hydrogen-bonding donor/acceptors at the periphery of TPVs such as with semicarbazone a precipitation as opposed to gelation was observed. Thus, the choice of the end functional groups and the number of hydrogen-bonding motifs in the TPV backbone holds the key and modulates the effective length of the chromophore, resulting in interesting optical properties Chapter 3A demonstrates successful incorporation of pristine and long-chain functionalized single-walled carbon nanotubes (SWNTs) in supramolecular organogels of 1 (Chart 2A.1) to give rise to new nanocomposites with interesting mechanical, thermal and electrical properties (Figure 3A.1). The SWNT promoted aggregation of 1 leads to quenching of the absorption and emission intensity of 1, increases the sol-to-gel transition temperature and increases the viscoelasticity of the composite gels. The composites were semiconducting in nature and showed enhanced electrical conductivity compared to that of 1 alone. Upon irradiation with a near IR laser at 1064 nm for 5 min, it was possible to selectively induce a gel-to-sol phase transition of the nanocomposites, while irradiation for even 30 min of the native organogel under identical conditions did not cause any gel-to-sol conversion Chapter 3B describes incorporation of multi-walled boron nitride nanotubes (BNNTs) and various functionalized BNNTs by Lewis bases such as trioctylamine (TOA), tributylamine (TBA), and triphenylphosphine (TPP) in the toluene gel of 1 (Chart 2A.1). Functionalized BNNTs were synthesized first and incorporation into the gel showed evidence of wrapping of the gelator molecules on to the BNNT surface presumably brought about by π-π stacking and van der Waals interactions (Figure 3B.1). This leads to the formation of densely packed and directionally aligned fibrous networks. Such “reinforced” aggregation of the gelator molecules in presence of doped BNNTs led to an increase in the sol-to-gel transition temperature and the solidification temperature of the gel-nanocomposites as revealed from differential scanning calorimetry. Rheological investigations of the gel-nanocomposites indicate that the flow properties of the resulting materials become resistant to applied stress upon incorporation of even a very low wt% of BNNTs. Finally, the increase in thermal conductivity of the nanocomposite compared to the gelator alone was observed for the temperature range of 0-60 oC which may make these composites potentially useful in various applications depending on the choice and the amount of BNNT loading in the composite. Chapter 3C presents first successful incorporation of graphene, and long aliphatic chain (n-dodecyl, n-hexadecyl) functionalized graphene in physical organogels formed by the aromatic oligo-phenylenevinylene (OPV) based gelator 1 (Chart 2A.1) and (non-aromatic) amino acid derived gelator. The large aromatic surfaces of gelator 1 serve as a host matrix for the incorporation of graphene and other nanocarbons (fullerene, SWNT). Such carbon nanomaterials (CNMs) exerted variable effects on the gelator through non-covalent interactions, due to their differences in shapes. Various microscopic images confirm the formation of densely wrapped fibrous networks for the resulting nanocomposites upon incorporation of CNMs. Variable temperature UV-vis and fluorescence spectra reveal CNMs mediated aggregation of the gelator molecules in solution and the presence of supramolecular interaction was evident from Raman spectroscopy. This ‘reinforced’ aggregation of the gelator molecules on doped CNMs was reflected in significantly enhanced thermal, mechanical and electrical properties of the nanocomposites. Rheological investigations of gels containing small amount of CNMs indicated that the flow of nanocomposites became resistant to applied stress at a very low wt-% of CNM incorporation (0.83 wt-%). An interesting synergistic behaviour was observed in case of the composite gel of OPV based LMOG containing a mixture of EG and SWNT when compared with other mixtures of CNMs in all combinations with EG. These studies are therefore of great contemporary interest as they provide molecular level control into the preparation of novel nanocomposites of LMOG and nanocarbons. Chapter 4 describes the synthesis of two low molecular mass organogelators based on tri-p-phenylenevinylene derivatives one of which could be designated as “acceptor” while the other one as “donor” (Figure 4.1). These were prepared specifically to show the inter-gelator interactions at the molecular level between each other through the donor-acceptor type of assembly to achieve control over their macroscopic properties. Intermolecular H-bonding, π-stacking and van der Waals forces are operational for both the individual and the mixture leading them to the gel formation in chosen organic solvents. Due to the photochromic nature of this class of molecules, they exhibited interesting photophysical properties. An efficient energy transfer was demonstrated from the mixture of donor-acceptor assemblies in solution. An array of four chromophores was built up by including two known dyes i.e. anthracene and rhodamine 6G for the energy transfer studies. Interestingly a cascade energy transfer was observed in the assembly of four chromophores in the series. This allowed building up of a wide range of light harvesting process, excitation at one end of which produces an emission at the other end of the assembly. Chapter 5A discusses the synthesis of new dicationic chromophoric phenylenedivinylene bis-N-alkyl pyridinium salts to study their hydrogelation behaviour through π-stacking and van der Waals interactions (Figure 5A.1). A crucial hydrophilic-hydrophobic balance in aqueous medium controls the gelation when a specific length of the aliphatic chain (n-octyl, 2) is appended on the both ends of the central aromatic core. The hydrogels showed considerably high gel-melting temperature and more viscoelastic solid-like properties with increasing concentrations of the gelator 2. Microscopic studies exhibited concentration dependent mixed fiber-coil morphology above its gelation concentration and only fibrillar networks below the gelation concentration (Figure 5A.1). Variable temperature, UV-visible and fluorescence spectroscopy showed aggregation induced emission switches for the self-assemblies promoted by addition of various salts (either cations or anions) in diluted solutions. Aggregation induced white-light emission could be achieved in aqueous medium either by tuning the concentration of the added salt or by varying the temperature of the mixture. Cyclic-voltametric studies indicate a reversible one-electron redox behavior for the chromophore which is also diffusion-controlled in nature. Lamellar type arrangement in the self-assembly was evident from the X-ray diffraction analysis. Gradual downfield shift in the proton signals of the 1H-NMR spectra upon heating suggest aromatic π-stacking and van der Waals interactions are operational among the gelator molecules and a balance with the electrostatic interactions lead to the physical gelation in water Chapter 5B presents supramolecular π-gel formation by phenylenedivinylene bis-N-alkyl pyridinium salts appended with terminal aliphatic hydrocarbon chains of different lengths (Chart 5A.1) in specific ratios of aliphatic alcohols and water mixture. The temperature- and the ratio-variation in the ethanol/water mixture showed the aggregation pattern of the self-assemblies promoted by electrostatic, aromatic π-stacking and van der Waals interactions among the individual gelators as observed under UV-visible and fluorescence spectroscopy. With increase in the number of carbon atoms in the aliphatic chain, greater gel-melting temperature, increased viscoelastic solid-like behavior and decreased fiber diameter was observed among the gelators. However, presence of excess hydrophobic moiety at the periphery, a precipitation as opposed to gelation was observed. Cyclic-voltametric studies show a one-electron reversible redox behavior for the chromophore and the redox potential decreases with increasing the aliphatic chain length. A diffusion-controlled redox behavior was observed for shorter aliphatic chains but the longer chains make the process diffusion-limited. The electrical conductivity studies show semiconducting behavior for individual compounds and the magnitude of current increases with increasing fiber diameter (with decreasing aliphatic chain length). Chapter 6A demonstrates the synthesis of new oligo-phenylenevinylene (OPV) analogues with pyridine end-functionality (Chart 6A.1) to show efficient supramolecular organogel formation through molecular complexation with tartaric acids (TA). The salt formation between the end-pyridine and TA exhibited a significant decrease in the IR stretching frequency of the carboxylic acid. Microscopic studies showed a nucleation induced growth of the fibers that essentially led to larger aggregate formation. A circular dichroism study demonstrated an opposite sense of chirality in the complexes for two optically active TA (L and D). The expression of chiral transcription in the achiral OPVs was manifested under atomic force microscopy which showed a specific handedness in the fibers for the complex with particular optically active TA. Fluorescence spectroscopic studies exhibited a remarkable red-shift of the emission maxima due to the J-type aggregation leading to the gel formation. In a particular condition, energy transfer from aggregated donor to aggregated acceptor was observed in the gel phase. A liquid crystalline behavior was observed under polarized optical microscopy as well. Chapter 6B describes selective Hg2+ sensors which have been achieved separately under ‘naked eye’ and fluorimetric method for two-coordination assisted conjugated pyridine-end oligo-phenylenevinylene moieties (Chart 6A.1, 1 and 2). A drastic visual color change was exhibited based on the conjugation length of such chromophores. The visual color change was more prominent in the chromophore containing five aromatic rings in a conjugation compared to only three aromatic rings. However, breakdown of the conjugation length in the chromophore unit through incorporation of semicarbazide moiety (isoniazid) (Chart 6B.1) leads to a lesser degree of change either visually or spectroscopically. Coincidently, the isoniazid moiety provides an extra motif for their anion sensing properties through the deprotonation of ‘N-H’ group. Thus a selective CN- sensor was achieved. The presence of H-bonding donor (-NH-) and acceptor (-CO-) group in the semicarbazone segment and the long n-hexadecyl chains induced a physical gel formation. Addition of Hg2+ or CN- to the gel leads to the gel-to-sol transition and further addition in a reverse order could induce a reversible gel formation. Effect of addition of Hg2+ and CN- to the gel was probed by UV-vis and 1H-NMR spectroscopy which showed significant spectral shifts in favor of their interactions.

Metamaterials are artificially structured materials which attain their unconventional macroscopic properties from their cellular configuration rather than their constituent chemical composition. The judicious design of this cellular structure opens the possibility to program and control the optical, mechanical, acoustic, or thermal responses of metamaterials. This Ph.D. dissertation focuses on scalable design and manufacturing strategies for optical and mechanical metamaterials.

The fabrication of optical metamaterials still relies heavily on low-throughput process such as electron beam lithography, which is a serial technique. Thus, there is a growing need for the development of high-throughput, parallel processes to make the fabrication of optical metamaterials more accessible and cost-effective. The first part of this dissertation presents a scalable manufacturing method, termed “roll-to-roll laser induced superplasticity” (R2RLIS), for the production of flexible optical metamaterials, specifically metallic near-perfect absorbers. R2RLIS enables the rapid and inexpensive fabrication of ultra-smooth metallic nanostructures over large areas using conventional CO₂ engravers or inexpensive diode lasers. Using low-cost metal/epoxy nanomolds, the minimum feature size obtained by R2RLIS was <40 nm, facilitating the rapid fabrication of flexible near-perfect absorbers at visible frequencies with the capability to wrap around non-planar surfaces.

The existing approaches for designing mechanical metamaterials are mostly ad hoc, and rely heavily on intuition and trial-and-error. A rational and systematic approach to create functional and programmable mechanical metamaterials is therefore desirable to unlock the vast design space of mechanical properties. The second part of this dissertation introduces a systematic, algorithmic design strategy based on Voronoi tessellation to create architected soft machines (ASMs) and twisting mechanical metamaterials (TMMs) with programmable motion and properties. ASMs are a new class of soft machines that benefit from their 3D-architected structure to expand the range of mechanical properties and behaviors achievable by 3D printed soft robots. On tendon-based actuation, ASMs deform according to the topologically encoded buckling of their structure to produce a wide range of motions such as contraction, twisting, bending, and cyclic motion. TMMs are a new class of chiral mechanical metamaterials which exhibit compression-twist coupling, a property absent in isotropic materials. This property manifests macroscopically and is independent of the flexible material chosen to fabricate the TMM. The nature of this compression-twist coupling can be programmed by simply tuning two design parameters, giving access to distinct twisting regimes and tunable onset of auxetic (negative Poisson’s ratio) behavior. Taking a metamaterial approach toward the design of soft machines substantially increases their number of degrees of freedom in deformation, thus blurring the boundary between materials and machines.