Academic literature on the topic 'Polymer Metal Composite'

Les métaux micro ou nanoporeux sont très attrayants notamment pour leur grande surface spécifique. Le désalliage dans un bain de métal liquide permet une dissolution sélective d'une espèce chimique (l'élément soluble) à partir d'un alliage d'origine (le précurseur) composé de l'élément soluble et d'un élément cible (qui deviendra nano/micro poreux) non soluble dans le bain de métal liquide. Quand le précurseur est plongé dans le bain de métal liquide, à son contact, l'élément soluble va se dissoudre dans le bain tandis que l'élément cible va en parallèle se réorganiser spontanément afin de former une structure poreuse. Quand l'échantillon est retiré du bain, il est sous la forme d'une structure bi-continue composée de deux phases : l'une étant la structure poreuse composée de l'élément cible et l'autre est une phase dans laquelle est présente l'élément du bain avec l'élément sacrificiel en solution solide. Cette phase peut être dissoute par une attaque chimique afin d’obtenir le métal nano/micro poreux. Les objectifs principaux de cette thèse sont l'élaboration et la caractérisation microstructurale et mécanique de 3 différents types de matériaux par désalliage dans un bain de métal liquide : des composites métal-métal (FeCr-Mg), des métaux poreux (FeCr) et des composites métal-polymère (FeCr-matrice époxy). Le dernier objectif est l'évaluation des possibilités d'utiliser la technique de désalliage dans un bain de métal liquide dans un contexte industriel. L'étude de la microstructure est basée sur des observations 3D faites par tomographie aux rayons X et des analyses 2D réalisées en microscopie électronique (SEM, EDX, EBSD). Pour mieux comprendre le désalliage, le procédé a été suivi in situ en tomographie aux rayons X et diffraction. Enfin, les propriétés mécaniques ont été évaluées par nanoindentation et compression<br>Nanoporous metals have attracted considerable attention for their excellent functional properties. The first developed technique used to prepare such nanoporous noble metals is dealloying in aqueous solution. Porous structures with less noble metals such as Ti or Fe are highly desired for various applications including energy-harvesting devices. The less noble metals, unstable in aqueous solution, are oxidized immediately when they contact water at a given potential so aqueous dealloying is only possible for noble metals. To overcome this limitation, a new dealloying method using a metallic melt instead of aqueous solution was developed. Liquid metal dealloying is a selective dissolution phenomenon of a mono-phase alloy solid precursor: one component (referred as soluble component) being soluble in the metallic melt while the other (referred as targeted component) is not. When the solid precursor contacts the metallic melt, only atoms of the soluble component dissolve into the melt inducing a spontaneously organized bi-continuous structure (targeted+sacrificial phases), at a microstructure level. This sacrificial phase can finally be removed by chemical etching to obtain the final nanoporous materials. Because this is a water-free process, it has enabled the preparation of nanoporous structures in less noble metals such as Ti, Si, Fe, Nb, Co and Cr. The objectives of this study are the fabrication and the microstructure and mechanical characterization of 3 different types of materials by dealloying process : (i) metal/metal composites (FeCr-Mg), (ii) porous metal (FeCr) (iii) metal/polymer composites (FeCr-epoxy resin). The last objective is the evaluation of the possibilities to apply liquid metal dealloying in an industrial context. The microstructure study was based on 3D observation by X-ray tomography and 2D analysis with electron microscopy (SEM, SEM-EDX, SEM-EBSD). To have a better understanding of the dealloying, the process was followed in situ by X-ray tomography and X-ray diffraction. Finally the mechanical properties were evaluated by nanoindentation and compression

This thesis describes the open-loop behavior of an ionic polymer metal composite (IPMC) strip as a novel actuator, the empirical force and position models, the control system and the improved dynamic characteristics with the feedback control implemented. Ionic polymer metal composite is a novel polymer in the class of electroactive polymers. IPMC consists of a base polymer coated with electrodes made up of highly conducting pure metals such as gold. The actuation behavior of IPMC can be attributed to the bending of an IPMC strip upon application of voltage across its thickness. The main reasons for the bending are ion migration on the application of voltage and swelling and contraction caused by water content. An experimental setup to study the open-loop force and tip displacement of an IPMC strip in a cantilever configuration was developed, and real time controllers were implemented. In open loop, the force response of the IPMC strip of dimensions 25 mm x 3.9 mm x 0.16 mm to a 1.2-V step input is studied. The open-loop rise time was 0.08 s and the percent overshoot was 131.62 %, while the settling time was about 10 s. Based on this open-loop step response using a least-square curve-fitting methodology, a fourth-order empirical transfer function from the voltage input to the force output was derived. The tip displacement response of an IPMC strip of dimensions 23 mm x 3.96 mm x 0.16 mm to a 1.2-V step input was also studied. The step response exhibited a 205.34 % overshoot with a rise time of 0.08 s, and the settling time was 27 s. A fourth-order empirical transfer function from the step input to the tip displacement as output was also derived. Based on the derived transfer functions lead-lag feedback controllers were designed for precision control of both force and displacement. The control objectives were to decrease the settling time and the percent overshoot, and achieve reference input tracking. After implementing the controllers, the percent overshoot decreased to 30% while the settling time was reduced to 1.5 s in case of force control. With position control, the settling time was reduced to 1 s while the percent overshoot decreased to 20%. Precision micro-scale force and position-control capabilities of the IPMC were also demonstrated. A 4 ?N force resolution was achieved, with a force noise of 0.904-?N rms. The position resolution was 20 ?m with a position noise of 7.6-?m rms.

Ionic Polymer Metal Composite (IPMC) is a class of electroactive polymer , that is receiving great attention due to its advantages of large bending deflection, low power consumption and driving voltage. Although there is still no commercial application of IPMC, it has been actively investigated by researchers for the past decade. The IPMC has been identified as a potential material to be used in the specific application of sensor and/or actuation, such as microgripper and micropump. This research deals with the characterisation of small scale IPMC with the ultimate objective to develop a simple microgripper to demonstrate the ability of the IPMC to grasp a micro object. A vision system has been developed to perform image processing to measure the displacement of IPMC. New algorithms of edge detection and displacement measurement have been introduced to characterise the IPMC. Comparison between laser sensor measurements and vision systems measurement has been carried out and the results showed that the vision system is a reliable measurement. Characterisation of small scale IPMC is carried out to prove the claim that miniaturization of IPMC is possible without degrading its performance. The characterisation of the IPMC actuator is divided into two major works - the displacement and blocked force measurements. The results showed that small scale characteristics are in line with the results that have been published by other researchers for larger scale of IPMC, hence supported the claim. The dynamic sensory behaviour of the IPMC has also been characterised. The results showed that the sensor functions are better in terms of producing consistent output signals when it is dehydrated. With such finding, the possibility of using the IPMC as the actuator and sensor at the same time for micro gripper application is not promising because the actuator needs to be fully hydrated in order to work better while the sensor is working better in a dehydrated condition. The final part in this research work is to develop a simple micro gripper. A two-finger microgripper with size of lOmm x 2rnrn x O.2mm is controlled by a vision feedback system to grasp small objects. For a demonstration purposes, an object with diameter of lmm was successfully grasped in 4.6 seconds.

Quantum Tunnelling Composite (QTC) is a metal polymer composite, commercialised and produced using a patented manufacture process. This process ensures that the metal particles within an elastomerie polymer matrix maintain a highly fractal surface morphology where nano-scale point features are retained on the particles and are coated in polymer. This structure provides unique electronic behaviour including very high resistivity, of order 10 ΜΩ, above the expected percolation threshold and an exponential increase in conductivity under all types of mechanical deformation. Increase in sample compression leads to a lower electrical resistance through the material. Current-voltage characteristics show a hysteresis effect due to current storage in the QTC material as a current is passed. The hysteresis is shown to be reduced as the applied compression on the material is increased until an Ohmic regime is reached at very high compressions, above 70% linear compression. At these high compressions Joule heating is also proven to occur as a result of the power dissipated in the sample by I-V cycling. The Joule heating is sufficient to influence the physical characteristics of the sample and expand it, creating a current limiting device. QTC samples loaded with acicular electro-conductive particles in small fractions, less than 10% by weight, showed less sensitivity to applied compression in terms of electrical response. These samples appear to exhibit less white noise characteristics and indicate a combination of field assisted quantum tunnelling and percolation mechanism, Intrinsically conductive QTC samples were developed. These were made using QTC granules mixed into a polymer solvent solution. Upon depositing onto electrodes the solvent was allowed to evaporate leaving the constituent polymer binding the QTC granules together, compressing them into a conductive state. Samples were exposed to volatile organic compound (VOC) vapours in the concentration range 10 ppm to 100,000 ppm, causing swelling and void filling in the binding polymer. Combinations of these processes caused an increase in sample resistance, from ~50 Ω to excess of 10 ΜΩ. Sample composition and physical parameters have significant effect upon the response characteristics of the sensors. A system of experiments was undertaken and optimum sample composition was determined. Response to environmental changes were investigated^ namely temperature response and response to varying concentration of exposed solvent. It was found that samples produced using Polyphenylene Oxide ( PPO) and Polyvinyl Chloride (PVC) based binding polymer were more resistant to temperature change from 30 С to 80 С due to their molecular structures. Sensor response to different vapour concentrations was found to exhibit two distinct response regimes. High concentration exposures were found to exhibit a swelling mechanism with a CASE-II diffusion model fitting the data well. Whereas at low concentrations a void-filling based change in sample dielectric constant was attributed to the electronic response to vapour exposure. These predictions were also confirmed using a Quartz Crystal Microbalance (QCM) to measure mass uptake of vapour molecules and polymer density under similar test conditions.

Ionic polymer-metal composites (IPMCs) are widely studied for their potential as electromechanical sensors and actuators. Bending of the IMPC depends on internal ion motion under an electric potential, and the addition of an ionic liquid and ionic self-assembled multilayer (ISAM) conductive network composite (CNC) strongly enhances bending and improves lifetime. Ion conducting polyelectrolytes poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) and Nafion® were incorporated into an ISAM CNC film with poly(allylamine hydrochloride) (PAH) and anionic gold nanoparticles actuators to further improve bending. CNC films were optimized for bending through pH adjustments in PAH and adding NaCl to the PAMPS and Nafion® solutions. PAMPS-containing actuators showed larger and faster bending than those containing Nafion® in the CNC. The IPMC actuator was also evaluated for its potential as a humidity sensor based on its relative humidity (RH) dependent steady-state current. The detection range is at least 10-80%RH, with 5%RH increment differentiation and likely better resolution. Effects of CNC presence and thickness were studied, in conjunction with ionic liquid at a range of RH values. A thin CNC (pH 4 PAH) produced the greatest current differentiation between RH values. The current's response speed to a large RH decrease was approximately 4 times faster than that of a fast commercial digital hygrometer. Additionally, the presence of a CNC and ionic liquid improved the current response time. These results indicate that an IPMC based humidity sensor using a CNC and ionic liquid is very promising and merits further study.<br>Master of Science

An increasing need for smaller, higher-power-density devices is driving the development of more advanced topologies for use in power architectures. The challenge, however, is to reduce the size of the passive components in circuit boards (e.g., the inductors), which are typically the most bulky. There are two ways to approach this problem. The first is to redesign the flux in the inductor in order to minimize its size; the second is to optimize the magnetic properties of the constituent magnetic materials, which include permeability, density, resistivity, core loss density, saturation magnetization value, fluidity, sintering temperature, and others. Compared to altering the nature of solid magnetic materials to reduce space constraints, modifying the magnetic composite is preferred. The most popular candidates for use in magnetic composites are magnetic powders and polymer composites. In particular, when metal alloys are chosen as magnetic powders they have high initial permeability, high saturation magnetization values, but low electrical resistivity. Since polymers can serve as insulation materials, mixing metal alloys with polymers will increase electrical resistivity. The most common metal alloy used is nickel-iron (permalloy) and Metglas. Since existing modeling methods are limited in (a) that multiphasic composites cannot be utilized and (b) the volume fraction of magnetic particles must be low, this investigation was designed to utilize FE (finite element) simulation to analyze how magnetic properties change with the distribution of permalloy powder or Metglas flakes in composites. The primary magnetic properties of interest in this study are permeability and core loss density. Furthermore two kinds of magnetic composites were utilized in this investigation: a benzocyclobutene (BCB) matrix-permalloy and a benzocyclobutene (BCB) matrix-permalloy-based amorphous alloy (Metglas 2705M) material. In our FE simulations, a BCB matrix-permalloy composite was utilized in a body-centered cubic model with half-diameter smaller particles serving as padding. The composite was placed in a uniform magnetic field surrounded by a material whose relative permeability was equal to zero in simulation. In comparison to experimental results, our model was able to predict permeability of composites with volume fraction higher than 52%. It must be noted, however, that although our model was able to predict permeability with only 10% off, it was less effective with respect to core loss density findings. The FE model also showed that permeability will increase with an increasing volume fraction of magnetic particles in the composite. To modify the properties of the composite material, the model of the BCB matrix-permalloy-Metglas composite followed model simulations up to the point at which flakes were inserted in BCB matrix-permalloy composite. The thickness of flakes was found to be an important factor in influencing resulting magnetic properties. Specifically, when the thickness of flakes decreased to quarter size at the same volume fraction, the permeability increased by 15%, while core loss density decreased to a quarter of the original value. The analysis described herein of the important relationship between magnetic properties and the composites is expected to aid in the development and design of new magnetic composite materials.<br>Master of Science

A novel metal-polymer composite is presented, comprised of a micron-sized nickel powder dispersed within a silicone polymer matrix. The composite is intrinsically electrically insulating, but displays a dramatic increase in conductivity under compression, tension and torsion. The electrical response to applied compression is characterised. Combined with electron microscopy, the large sensitivity to compression is shown to be due to the uniquely spiky morphology of the filler particles. Low mechanical energy mixing techniques are essential for retaining these sharp tips. In addition, wetting of the nickel particles by the silicone polymer is highly effective, resulting in negligible inter-particle contact between metallic grains even at very high loadings and compressions. Current-voltage characteristics are highly non-linear, displaying peaks, hysteresis, negative differential resistance, trap-filling and radio frequency emission. Evidence points towards an inter-particle conduction mechanism dominated by field emission and Fowler-Nordheim tunnelling, made possible by localised field enhancements at the sharp tips. A novel mechanism of grain charging and the 'pinching-off of conduction pathways is also suggested. Granular forms of the composite display dramatic increases in resistance when exposed to organic solvent vapours, transduced by a polymer swelling mechanism. Responses are dependent upon vapour concentration, and differential responses are obtained with other polymers, indicating excellent potential for applications in artificial olfactory devices (electronic noses). Polymer-solvent interactions follow both Fickian and anomalous diffusion characteristics, and follow basic trends predicted by solubility parameters.

Corrosion is a persistent problem faced by manmade structures made up of metal alloys. Aluminum 2024-T3 is high strength, light weight alloy used in aerospace applications. It suffers from the problem of corrosion due to its composition. Cold rolled steel is employed in structural applications but undergoes severe corrosion when exposed to corrosive conditions. Coatings are one of the best avenues to protect metal alloys from the corrosion. Traditional coating systems such as barrier type coatings, metal rich coatings, and inhibitor containing coatings have their own drawbacks. Conducting polymers (CPs), such as polypyrrole (PPy) can be used for the corrosion protection of the metals. Redox activity in conjunction with corrosion inhibiting ion release ability make CPs as a promising candidate for the replacement for hexavalent chromates. However CPs porous nature, inherent insolubility, stiff chains, and poor mechanical properties pose significant hindrance towards their implementation in coatings. In order to overcome the problems associated with the CPs and to extract maximum functionality out of them, conducting polymer containing composites (CPCC) were developed. CPCC combines CPs with inorganic pigments in unique ways and pave for excellent properties. In this work, series of composites of PPy/Inorganic pigments (aluminum flakes, iron oxide, micaceous iron oxide, and titanium dioxide) were synthesized by ecofriendly, facile chemical oxidative polymerization. Core and shell morphologies of PPy with titanium dioxide and iron oxide were synthesized and employed for the corrosion protection of cold rolled steel substrate. Various dopants such as phosphate, nitrate, molybdate, vanadate, and tungstate were incorporated in the backbone of PPy. These composites were characterized for morphology, elemental composition, and conductivity by various techniques. Furthermore coatings based on these composite pigments were formulated on Aluminum 2024-T3 and cold rolled steel substrates. These coatings were exposed to salt spray and prohesion test conditions and electrochemically evaluated against corrosion by Electrochemical Impedance Spectroscopy (EIS), DC Polarization, galvanic coupling and Scanning Vibrating Electrode Technique (SVET). Effect of solvent in the composite synthesis and PPy morphology in the final composite on the protective properties of coating was investigated. Effect of corrosion inhibiting anions on the final performance properties was also evaluated.<br>U.S. Army Research Laboratory (Grant No. W911NF-09-2-0014, W911NF-10-2-0082, and W911NF-11-2-0027)

This dissertation describes the development of a coupled model for the analysis of a novel polymer/metal composite (IPMC) actuator under large external voltage. A general continuum model describing the transport and deformation processes of solid polymer electrolyte is proposed. The formulation is based on global integral postulates for the mass conservation, charge conservation, momentum equilibrium, the first law of thermodynamics, and the second law of thermodynamics. The global equations are localized in the volume and on the material surfaces bounding the polymer. The model is simplified to a three-component system comprised of a fixed negatively charged polymeric matrix, protons, and free water molecules within the polymer matrix. Among these species, water molecules are considered as the dominant specie responsible for the deformation of the IPMC actuators. In this work, the electrochemical process occurring at both electrodes is analyzed as boundary conditions during the deformation of actuator in the regime of large voltage (over 1.2 V). These are used in the framework of overpotential theory to develop boundary conditions for the water transport in the bulk of polymer. The proposed coupled model successfully captures the stress relaxation phenomenon due to water redistribution governed by diffusion. The fabrication process are described, and experiments including the role of initial water content on the electro-mechanical response of the actuator are also discussed. Comparison of simulations and experimental data showed good agreement.