Auswahl der wissenschaftlichen Literatur zum Thema „Colloidal agglomeration“

Colloidal systems consisting of monodomain superparamagnetic nanoparticles have been used in biomedical applications, such as the hyperthermia treatment for cancer. In this type of colloid, called a nanofluid, the nanoparticles tend to agglomeration. It has been shown experimentally that the nanoparticle coating plays an important role in the nanoparticle dispersion stability and biocompatibility. However, theoretical studies in this field are lacking. In addition, the ways in which the nanoparticle coating influences the magnetic properties of the nanoparticles are not yet understood. In order to fill in this gap, this study presents a numerical simulation model that elucidates how the nanoparticle coating affects the nanoparticle agglomeration tendency as well as the effective magnetic relaxation time of the system. To simulate the self-organization of the colloidal nanoparticles, a stochastic Langevin dynamics method was applied based on the effective Verlet-type algorithm. The Néel magnetic relaxation time was obtained via the Coffey method in an oblique magnetic field, adapted to the local magnetic field on a nanoparticle.

Environmental contextThe fate of nanomaterials in the environment is related to their colloidal stability. Although numerous studies have examined their homoagglomeration, their low concentration and the presence of high concentrations of natural particles implies that heteroagglomeration rather than homoagglomeration is likely to occur under natural conditions. In this paper, two state-of-the art analytical techniques were used to identify the conditions under which nanosilver was most likely to form heteroagglomerates in natural waters. AbstractThe environmental risk of nanomaterials will depend on their persistence, mobility, toxicity and bioaccumulation. Each of these parameters is related to their fate (especially dissolution, agglomeration). The goal of this paper was to understand the heteroagglomeration of silver nanoparticles in natural waters. Two small silver nanoparticles (nAg, ~3nm; polyacrylic acid- and citrate-stabilised) were covalently labelled with a fluorescent dye and then mixed with colloidal silicon oxides (SiO2, ~18.5nm) or clays (~550nm SWy-2 montmorillonite). Homo- and heteroagglomeration of the nAg were first studied in controlled synthetic waters that were representative of natural fresh waters (50μg Ag L–1; pH 7.0; ionic strength 10–7 to 10–1 M Ca) by following the sizes of the nAg by fluorescence correlation spectroscopy. The polyacrylic acid-coated nanosilver was extremely stable under all conditions, including in the presence of other colloids and at high ionic strengths. However, the citrate-coated nanosilver formed heteroaggregates in presence of both colloidal SiO2 and clay particles. Nanoparticle surface properties appeared to play a key role in controlling the physicochemical stability of the nAg. For example, the polyacrylic acid stabilized nAg-remained extremely stable in the water column, even under conditions for which surrounding colloidal particles were agglomerating. Finally, enhanced dark-field microscopy was then used to further characterise the heteroagglomeration of a citrate-coated nAg with suspensions of colloidal clay, colloidal SiO2 or natural (river) water.

The study investigated the phenomenon of the fast aggregation of single-domain magnetic iron oxide nanoparticles in stable aqueous colloidal suspensions due to the presence of a radio-frequency (RF) magnetic field. Single-domain nanoparticles have specific magnetic properties, especially the unique property of absorbing the energy of such a field and releasing it in the form of heat. The localized heating causes the colloid to become unstable, leading to faster agglomeration of nanoparticles and, consequently, to rapid sedimentation. It has been shown that the destabilization of a stable magnetic nanoparticle colloid by the RF magnetic field can be used for the controlled filtration of larger agglomerates of the colloid solution. Two particular cases of stable colloidal suspensions were considered: a suspension of the bare nanoparticles in an alkaline solution and the silica-stabilized nanoparticles in a neutral solution. The obtained results are important primarily for biomedical applications and wastewater treatment.

The structure, optical and magneto-optical properties of colloidal solutions of iron oxide nanoparticles obtained by pulsed ablation in distilled water, both without additives and with various functional additives: gold-hydrochloric acid, silicon oxide, and polyvinylpyrrolidone, have been studied. It is shown that the main magnetic phase is magnetite Fe3O4. The size distribution of nanoparticles and the degree of their agglomeration depend on the additives. In the absence of the latter, a very wide of size distributions and strong agglomeration of particles are observed. The narrowest distribution curve with a maximum corresponding to ~7 nm and an almost complete absence of agglomeration are observed for particles synthesized in the presence of polyvinylpyrrolidone. The shape of the spectral dependence of magnetic circular dichroism, which generally corresponds to the spectrum of magnetite, undergoes some modifications for various additives, which is associated with defects in the distribution of iron ions between different positions in the crystal. Keywords: pulsed laser ablation, nanoparticles, colloidal solutions, magnetite, magnetic circular dichroism.

This research aims to investigate the agglomeration processes of magnetoresponsive functionalized nanocluster suspensions in a magnetic field, as well as how these structures impact the behaviour of these suspensions in biomedical applications. The synthesis, shape, colloidal stability, and magnetic characteristics of PEG-functionalized nanoclusters are described in this paper. Experiments using TEM, XPS, dynamic light scattering (DLS), VSM, and optical microscopy were performed to study chain-like agglomeration production and its influence on colloidal behaviour in physiologically relevant suspensions. The applied magnetic field aligns the magnetic moments of the nanoclusters. It provides an attraction between neighbouring particles, resulting in the formation of chains, linear aggregates, or agglomerates of clusters aligned along the applied field direction. Optical microscopy has been used to observe the creation of these aligned linear formations. The design of chain-like structures can cause considerable changes in the characteristics of ferrofluids, ranging from rheological differences to colloidal stability changes.

Nanomaterials are widely used in various fields because of their own advantages. When the particle size of the material is reduced to the nanometer level, it will lead to new characteristics of acoustic, optical, electrical, magnetic, and thermal properties. This will greatly enrich the research content of the material and is expected to get new uses. Therefore, the preparation technology of nanomaterials is one of the current research hotspots and has broad application prospects. At present, the most commonly used preparation techniques are hydrothermal method and sol-gel method, but not all crystals grow in a hydrothermal environment, so this paper adopts the sol-gel method for preparation. However, in the preparation of nanocolloids, agglomeration often occurs between colloidal nanoparticles. In order to avoid the agglomeration between particles, this paper adopts an appropriate method to disperse the particles. In order to further explore the stability of nanocolloids, the colloidal film material prepared by the cadmium sulfide (CdS) sol method was used as the research sample. It also proposes a sol preparation method incorporating ultrasonic waves and further discusses the kinetic characteristics. The research results show that the sedimentation velocity of 1 nm cadmium sulfide nanocolloids in water is 1.3 × 10−12 (m/s) prepared by colloid of cadmium sulfide.

Abstract A study of like-charged, bimodal colloidal suspensions was conducted in microgravity aboard the International Space Station as part of NASA's Advanced Colloids Experiments-Heated-2 (ACE-H-2) experiments. Samples comprised of silsesquioxane microparticles (600 nm) and zirconia nanoparticles (5–15 nm) in 1.5 pH nitric acid were mixed and allowed to agglomerate over time while being imaged with NASA's Light Microscopy Module (LMM). The samples contained 1% of microparticles with varying concentrations of nanoparticles in 0.1%, 0.055%, and 0.01% by volume. Digital images were captured periodically by the LMM over 12 days. Image analysis, including cluster size and distribution, was performed in Python using the “Colloidspy” package. The study found that cluster size had increased over time in at least seven of nine samples, but two samples exhibited nonlinear growth rates, while others showed very slow growth with cluster sizes two orders of magnitude greater than the free microparticles. We hypothesize that all samples experienced nonlinear growth, but early transient effects after mixing were missed due to timing limitations in image acquisition. Transport limitations of clusters in these systems may have dominated agglomeration behavior in microgravity, despite the samples being thermodynamically unstable, but more study is required.

The aim of this work is to look into the applicability of Discrete Element Modelling (DEM) coupled to Computational Fluid Dynamics (CFD) to simulate micro-scale colloidal particles immersed in fluid. Numerical methods were implemented through the commercial framework of EDEM2.3. As opposed to dissolved matter, which behaves as a continuum within the fluid medium, particulate matter is made of discrete entities that interact amongst themselves, and with the fluid and any physical boundaries. Particulate matter is ubiquitous in many purification processes that would beneficiate from having an easy way to model particle dynamics immersed in water. In an effort to understand better the dynamics of particle deposition under surface forces and hydraulic forces, a micro-scale numerical model was built adopting both a mechanistic and a statistical approach to represent the forces involved in colloidal suspension. The primary aim of the model was to simulate particle aggregation, deposition and cluster re-suspension in real world micro-systems. Case studies include colloidal flocculation in a constricted tube, and colloidal fouling around membrane filtration feed spacers. This work used a DEM-CFD coupling method that combined the DEM particle flow simulation with hydrodynamics forces from a velocity field computed through CFD. It also implemented boundary-particle and particle-particle interactions by enabling the modelling of surface and interfacial forces. Two kinds of coupling method were considered: two-way and one-way coupling. Two-way coupling is suitable for high particle concentration flow where particle loading affects the hydrodynamics. One-way coupling is suitable for dispersed particle configuration where the flow field is assumed to be undisturbed by the particles. The advantages and drawbacks of both techniques for micron-size particles were investigated. EDEM 2.3 was customised with plug-ins to implement Van der Waals forces and Brownian forces and its post-processing features offered the ability to investigate easily the microparticles behaviour under the influence of fluid forces. In this context, DEM-CFD modelling using EDEM 2.3 represents an improvement on previously published works as it enables higher visibility and reproducibility along with increasing the number of potential users of such modelling. Emphasis was given in presenting original findings and validation results that illustrate DEMCFD applicability, with respect to modelling of hydraulically mediated colloidal surface interaction; while highlighting factors that limit the ability of the technique. For instance, the effect of particle disturbance on the surrounding medium currently proves difficult to model.

Extensive attention has been paid to consolidate nanoparticles into nanocrystalline components that possess better properties than their coarse-grained counterparts. Nanocrystalline monolithic tungsten (W) has been envisaged to possess better properties than coarse-grained tungsten and to improve the performance of many military components. Commercially available nano-W powders were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and Brunauer, Emmett, and Teller (BET) measurement. While the bulk of nano-W powders consisted of bcc-W as confirmed by XRD and TEM, much of their surface consisted of WO3 with traces of WO2 and WC. Despite the irregular morphology and agglomerates greater than 1 m in size, the diameter of individual nano-W powders ranged from 30 to 100 nm with a surface area of 10.4 m2/g. To obtain green bodies of higher densities and more homogeneous microstructures after consolidation, W nanopowders were de-agglomerated in water and slip cast in plaster molds. De-agglomeration in water was conducted by repeated ultrasonication, washing, centrifuge and pH adjustment. The change in particle size and morphology was examined via SEM. After the initial surface oxide was removed by repeated washing, the reactivity of W nanoparticles to water was somewhat inhibited. Increasing the number of cycles for ultrasonication and washing increased the pH, the degree of de-agglomeration and the stability of W suspension. The zeta potential was more negative with increasing pH and most negative at pH values close to 5. Viscosity also decreased with increasing pH and reached a minimum at a pH 5. To obtain the highest solid loading with the lowest viscosity, the pH value of W suspension was adjusted to 5 using aqueous tetramethylammonium hydroxide solutions. The relative density of the slip cast increased with longer ultrasonic time, increasing slurry pH up to 5, and consequent increase in solids loading. Smaller particles were separated from larger ones by ultrasonication, washing with water and centrifugation. At a 27.8 vol.% solids loading, the size-separated fine W slurry was slip cast into pellets with relative green densities up to 41.3 % and approximate particle sizes of 100 nm. W powders were also ultrasonicated in aqueous poly (ethyleneimine) (PEI) solutions with various concentrations. SEM examinations of particle sizes showed that 1 wt.% PEI led to the optimum dispersion and ultrasonication for longer time with a low power resulted in better dispersion. 0.5 g of W powders were ultrasonicated in 10 ml aqueous poly (allylamine hydrochloride) (PAH) solutions with molar concentrations ranging from 0.01 to 0.05 M. W suspensions with 0.03 M and 0.04 M PAH after two washing cycles showed improved dispersion. Cold isostatic pressing can further increase the green density following slip casting. Sintered slip casts made from de-agglomerated nanoparticle W showed a lower density, more uniform microstructure, smaller grains and smaller pores than the sintered dry pressed pellets.
M.S.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Materials Science & Engr MSMSE

Addition of nano particles to cooling fluids has shown marked improvement in the heat transfer capabilities. Nanofluids, liquids that contain dispersed nanoparticles, are an emerging class of fluids that have great potential in many applications. There is a need to understand the fundamental behavior of nano dispersed particles with respect to their agglomeration characteristics and how it relates to the heat transfer capability. Such an understanding is important for the development and commercialization of nanofluids. In this work, the stability of nano particles was studied by measuring the zeta potential of colloidal particles, particle concentration and size. Two different sizes of silica nano particles, 10 nm and 20 nm are used in this investigation at 0.2 vol. % and 0.5 vol. % concentrations. The measurements were made in deionized (DI) water, buffer solutions at various pH, DI water plus HCl acid solution (acidic pH) and DI water plus NaOH solution (basic pH). The stability or instability of silica dispersions in these solutions was related to the zeta potential of colloidal particles and confirmed by particle sizing measurements and independently by TEM observations. Low zeta potentials resulted in agglomeration as expected and the measured particle size was greater. The heat transfer characteristics of stable or unstable silica dispersions using the above solutions were experimentally determined by measuring heat flux as a function of temperature differential between a nichrome wire and the surrounding fluid. These experiments allowed the determination of the critical heat flux (CHF), which was then related to the dispersion characteristics of the nanosilica in various fluids described above. The thickness of the diffuse layer on nano particles was computed and experimentally confirmed in selected conditions for which there was no agglomeration. As the thickness of the diffuse layer decreased due to the increase in salt content or the ionic content, the electrostatic force of repulsion cease to exist and Van der Waal's force of agglomeration prevailed causing the particles to agglomerate affecting the CHF. The 10nm size silica particle dispersions showed better heat transfer characteristics compared to 20nm dispersion. It was also observed that at low zeta potential values, where agglomeration prevailed in the dispersion, the silica nano particles had a tendency to deposit on the nickel chromium wire used in CHF experiments. The thickness of the deposition was measured and the results show that with a very high deposition, CHF is enhanced due to the porosity on the wire. The 10nm size silica particles show higher CHF compared to 20nm silica particles. In addition, for both 10nm and 20nm silica particles, 0.5 vol. % concentration yielded higher heat transfer compared to 0.2 vol. % concentration. It is believed that although CHF is significantly increased with nano silica containing fluids compared to pure fluids, formation of particle clusters in unstable slurries will lead to detrimental long time performance, compared to that with stable silica dispersions.
M.S.M.S.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science and Engineering

Un support catalytique en alumine doit avoir des propriétés mécaniques et thermiques adéquates, et favoriser un transfert de masse et de chaleur approprié. Ces propriétés dépendent de la texture du support, qui est le résultat du procédé de fabrication. Cette thèse se concentre sur l’opération unitaire de peptisation et malaxage, qui implique la dispersion d’une poudre de boehmite dans une solution acide. Une base est ensuite ajoutée pour induire l’agglomération des particules de boehmite dispersées. Ce procédé, réalisé sous agitation, permet de contrôler la taille et la structure des agglomérats d’alumine qui constitueront le support solide du catalyseur. Ce travail vise à modéliser la structure solide de l’alumine en fonction des paramètres physico-chimiques qui dirigent l’agglomération colloïdale, en absence des forces hydrodynamiques. Afin d’étudier l’impact du pH, de la force ionique et de la concentration sur la cinétique de coagulation, trois techniques expérimentales sont utilisées : la diffusion dynamique de la lumière (DLS), la diffusion des rayons X aux petits angles (SAXS) et la microscopie électronique à transmission (STEM). Les résultats expérimentaux sont interprétés à travers l’équation du bilan de population, alimentée par un modèle de dynamique Brownienne. Les résultats du bilan de population sont ensuite utilisés pour paramétrer un modèle morphologique d’agglomération, afin de simuler de grands volumes de la structure poreuse du solide d’alumine. Le modèle morphologique fait partie des nouvelles contributions de cette thèse, et permet de calculer les propriétés texturales d’un grain de boehmite
An alumina catalyst carrier must have adequate mechanical and thermal properties, and promote an appropriate mass and heat transfer. These properties depend on the carrier texture, which is the result of its manufacturing process. Our study focuses on the peptization and kneading process, which involves the dispersion of boehmite powder in an acid solution. A base is then added to induce the agglomeration of dispersed boehmite particles. This process, performed under mixing, enables to tune the size and structure of the boehmite agglomerates that will build the solid catalyst carrier. This work aims at modeling the alumina solid structure depending on the physical-chemical parameters that drive the colloidal agglomeration when no hydrodynamic forces are present. In order to study the impact of pH, ionic strength and concentration on the coagulation kinetics, three experimental techniques are used: Dynamic Light Scattering (DLS), Small Angle X-Ray Scattering (SAXS) and Scanning Transmission Electron Microscopy (STEM). The results of the experimental data are interpreted in terms of the population-balance equation, where the size-structure relationship is given by a Brownian dynamics model. The results of the population-balance model are then used as inputs for a morphological agglomeration model, to simulate large volumes of the porous structure of the real alumina solid. Such a model is one of the new contributions of this work, and enables to compute textural properties of a boehmite grain

Wet granulation process requires the addition of a coating agent or binder, typically composed of surfactants, water, plasticizers and fillers. In dry granulation however, the coating agent is added to the system in the form of fine solid particles. Our goals are to investigate the particles behaviour and agglomeration mechanism in dry and aqueous systems at the micro and meso scales, and also, to develop predictive methodologies and theoretical tools of investigation allowing to choose the adequate binder and to formulate the right coating solution. In this study we chose materials widely used in food and pharmaceutical industries, including; coating agents such as Hydroxypropyl-methylcellulose (HPMC) and Ethyl cellulose (EC), binders such as Polyvinylpyrrolidone (PVP) and Microcrystalline cellulose (MCC), hydrophobic filler such as Stearic acid (SA) and plasticizer such as Polyethylene glycol (PEG). A successful granulation requires good affinity between host and guest particles. In this context, in the first part of this work, two approaches to predict the binder-substrate affinity in dry and in aqueous media were compared; one based on the work of adhesion and the other based on the ideal tensile strength. The concept of ideal tensile strength was extended to ternary systems and applied for granulation in aqueous media. The developed approaches were thereafter tested for various systems (composed of PVP, MCC, HPMC, SA, EC, PEG and water) and compared to experimental observations. Approaches yielded results in good agreement with the experimental observations, but the work of adhesion approach might give more accurate affinity predictions on the particles affinity than the ideal tensile strength approach. Both approaches predicted that HPMC is a good binder for MCC. Results also indicated that PEG has a good affinity with HPMC and SA. In a second part of our work, we used mesoscale simulations and experimental techniques to investigate the structure of agglomerates formed in aqueous colloidal formulations used in coating and granulation processes. For the simulations, dissipative particle dynamics (DPD) and a coarse-grained approach were used. In the DPD method, the compounds were described as a set of soft beads interacting according to the Flory-Huggins model. The repulsive interactions between the beads were evaluated using the solubility parameter (δ) as input, where, δ was calculated by all-atom molecular simulations. The mesoscale simulation results were compared to experimental results obtained by Cryogenic-SEM, particle size distribution analysis and DSC technique. According to the DPD simulations, HPMC polymer is a better stabilizing agent for SA than PVP and MCC. In addition, HPMC is able to cover the SA particle with a thick layer ant to adsorb in depth into its inner core, preventing SA agglomeration and crystal growth. But, for high amounts of SA (above 10% (w/w)), HPMC is unable to fully stabilize SA. We also found that PEG polymer diffuses inside HPMC chains thereby extending and softening the composite polymer. Experimental results presented similar trends; particle size distribution analysis showed that in the presence of HPMC, for low percentages of SA (below 10% (w/w)), the majority of SA particles are below 1 μm in diameter. SEM images revealed that HPMC surrounds SA crystals with a hatching textured film and anchors on their surface.

This thesis presents a mathematical model of the evaporation of colloidal sol droplets suspended within an atmosphere consisting of water vapour and air. The main purpose of this work is to investigate the causes of the morphologies arising within the powder collected from a spray dryer into which the precursor sol for Synroc™ is sprayed. The morphology is of significant importance for the application to storage of High Level Liquid Nuclear Waste. We begin by developing a model describing the evaporation of pure liquid droplets in order to establish a framework. This model is developed through the use of continuum mechanics and thermodynamic theory, and we focus on the specific case of pure water droplets. We establish a model considering a pure water vapour atmosphere, and then expand this model to account for the presence of an atmospheric gas such as air. We model colloidal particle-particle interactions and interactions between colloid and electrolyte using DLVO Theory and reaction kinetics, then incorporate these interactions into an expression for net interaction energy of a single particle with all other particles within the droplet. We account for the flow of material due to diffusion, advection, and interaction between species, and expand the pure liquid droplet models to account for the presence of these species. In addition, the process of colloidal agglomeration is modelled. To obtain solutions for our models, we develop a numerical algorithm based on the Control Volume method. To promote numerical stability, we formulate a new method of convergence acceleration. The results of a MATLAB™ code developed from this algorithm are compared with experimental data collected for the purposes of validation, and further analysis is done on the sensitivity of the solution to various controlling parameters.

Sizing (hydrophobization) is one of the most important process steps within the added-value chain of about 1/3rd of the worldwide produced paper & board products. Even though sizing with so-called reactive sizing agents, such as alkenyl succinic anhydride (ASA) was implemented in the paper industry decades ago, there is no total clarity yet about the detailed chemical and physical mechanisms that lead to their performance. Previous research was carried out on the role of different factors influencing the sizing performance, such as bonding between ASA and cellulose, ASA hydrolysis, size revision as well as the most important interactions with stock components, process parameters and additives during the paper making process. However, it was not yet possible to develop a holistic model for the explanation of the sizing performance given in real life application. This thesis describes a novel physico-chemical approach to this problem by including results from previous research and combining these with a wide field of own basic research and a newly developed method that allows tracing back the actual localization of ASA within the sheet structure. The carried out measurements and trial sets for the basic field of research served to evaluate the stock and process parameters that most dominantly influence the sizing performance of ASA. Interactions with additives other than retention aids were not taken into account. The results show that parameters, such as the content of secondary fibers, the degree of refining, the water hardness as well as the suspension conductivity, are of highest significance. The sample sets of the trials with the major impacting parameters were additionally analyzed by a newly developed localization method in order to better understand the main influencing factors. This method is based on optical localization of ASA within the sheet structure by confocal white light microscopy. In order to fulfill the requirements at magnification rates of factor 100 optical zoom, it was necessary to improve the contrast between ASA and cellulose. Therefore, ASA was pretreated with an inert red diazo dye, which does not have any impact on neither the sizing nor the handling properties of ASA. Laboratory hand sheets that were sized with dyed ASA, were analyzed by means of their sizing performance in correlation to measurable ASA agglomerations in the sheet structure. The sizing performance was measured by ultrasonic penetration analysis. The agglomeration behavior of ASA was analyzed automatically by multiple random imaging of a sample area of approx. 8650 µm² with a minimum resolution for particles of 500 nm in size. The gained results were interpreted by full factorial design of experiments (DOE). The trials were carried out with ASA dosages between 0% and 0.8% on laboratory hand sheets, made of 80% bleached eucalyptus short fiber kraft pulp and 20% northern bleached softwood kraft pulp, beaten to SR° 30, produced with a RDA sheet former at a base weight of 100 g/m² oven dry. The results show that there is a defined correlation between the ASA dosage, the sizing performance and the number and area of ASA agglomerates to be found in the sheet structure. It was also possible to show that the agglomeration behavior is highly influenced by external factors like furnish composition and process parameters. This enables a new approach to the explanation of sizing performance, by making it possible to not only examine the performance of the sizing agent, but to closely look at the predominant position where it is located in the sheet structure. These results lead to the explanation that the phenomenon of sizing is by far not a pure chemical process but rather a more physical one. Based on the gained findings it was possible so far to optimize the ASA sizing process in industrial-scale by means of ~ 50% less ASA consumption at a steady degree of sizing and improved physical sheet properties.

Agglomeration of nanoparticles occurs in a number of colloidal systems related, for example, to material processing and drug delivery. The present work is motivated by the need to improve fundamental understanding of the agglomeration and structure formation processes that occur in catalyst inks used for the fabrication of polymer electrolyte fuel cells (PEMFCs). Particle dynamics simulations are performed to investigate agglomeration under various conditions. The interaction between particles is defined using realistic physical potentials, rather than commonly used potential models, and a novel analysis of the agglomeration and structure formation process is performed using network science concepts. The simulated systems correspond to catalyst inks consisting primarily of carbon nanoparticles in solution. The effect of various conditions such as different force magnitude, shape of the force function, concentration etc. are investigated in terms of network science parameters such as average degree and shortest path. An "agglomeration timescale" and a "restructuring timescale" introduced to interpret the evolution of the agglomeration process suggest that the structure, which has a strong impact on the performance of the eventual catalyst layer, can be controlled by tuning the rate at which particles are added based on the restructuring timescale.
Graduate

Sizing (hydrophobization) is one of the most important process steps within the added-value chain of about 1/3rd of the worldwide produced paper & board products. Even though sizing with so-called reactive sizing agents, such as alkenyl succinic anhydride (ASA) was implemented in the paper industry decades ago, there is no total clarity yet about the detailed chemical and physical mechanisms that lead to their performance. Previous research was carried out on the role of different factors influencing the sizing performance, such as bonding between ASA and cellulose, ASA hydrolysis, size revision as well as the most important interactions with stock components, process parameters and additives during the paper making process. However, it was not yet possible to develop a holistic model for the explanation of the sizing performance given in real life application. This thesis describes a novel physico-chemical approach to this problem by including results from previous research and combining these with a wide field of own basic research and a newly developed method that allows tracing back the actual localization of ASA within the sheet structure. The carried out measurements and trial sets for the basic field of research served to evaluate the stock and process parameters that most dominantly influence the sizing performance of ASA. Interactions with additives other than retention aids were not taken into account. The results show that parameters, such as the content of secondary fibers, the degree of refining, the water hardness as well as the suspension conductivity, are of highest significance. The sample sets of the trials with the major impacting parameters were additionally analyzed by a newly developed localization method in order to better understand the main influencing factors. This method is based on optical localization of ASA within the sheet structure by confocal white light microscopy. In order to fulfill the requirements at magnification rates of factor 100 optical zoom, it was necessary to improve the contrast between ASA and cellulose. Therefore, ASA was pretreated with an inert red diazo dye, which does not have any impact on neither the sizing nor the handling properties of ASA. Laboratory hand sheets that were sized with dyed ASA, were analyzed by means of their sizing performance in correlation to measurable ASA agglomerations in the sheet structure. The sizing performance was measured by ultrasonic penetration analysis. The agglomeration behavior of ASA was analyzed automatically by multiple random imaging of a sample area of approx. 8650 µm² with a minimum resolution for particles of 500 nm in size. The gained results were interpreted by full factorial design of experiments (DOE). The trials were carried out with ASA dosages between 0% and 0.8% on laboratory hand sheets, made of 80% bleached eucalyptus short fiber kraft pulp and 20% northern bleached softwood kraft pulp, beaten to SR° 30, produced with a RDA sheet former at a base weight of 100 g/m² oven dry. The results show that there is a defined correlation between the ASA dosage, the sizing performance and the number and area of ASA agglomerates to be found in the sheet structure. It was also possible to show that the agglomeration behavior is highly influenced by external factors like furnish composition and process parameters. This enables a new approach to the explanation of sizing performance, by making it possible to not only examine the performance of the sizing agent, but to closely look at the predominant position where it is located in the sheet structure. These results lead to the explanation that the phenomenon of sizing is by far not a pure chemical process but rather a more physical one. Based on the gained findings it was possible so far to optimize the ASA sizing process in industrial-scale by means of ~ 50% less ASA consumption at a steady degree of sizing and improved physical sheet properties.:Acknowledgment I Abstract III Table of Content V List of Illustrations XI List of Tables XVI List of Formulas XVII List of Abbreviations XVIII 1 Introduction and Problem Description 1 1.1 Initial Situation 1 1.2 Objective 2 2 Theoretical Approach 3 2.1 The Modern Paper & Board Industry on the Example of Germany 3 2.1.1 Raw Materials for the Production of Paper & Board 5 2.2 The Sizing of Paper & Board 8 2.2.1 Introduction to Paper & Board Sizing 8 2.2.2 The Definition of Paper & Board Sizing 10 2.2.3 The Global Markets for Sized Paper & Board Products and Sizing Agents 11 2.2.4 Physical and Chemical Background to the Mechanisms of Surface-Wetting and Penetration 13 2.2.4.1 Surface Wetting 14 2.2.4.2 Liquid Penetration 15 2.2.5 Surface and Internal Sizing 17 2.2.6 Sizing Agents 18 2.2.6.1 Alkenyl Succinic Anhydride (ASA) 19 2.2.6.2 Rosin Sizes 19 2.2.6.3 Alkylketen Dimer (AKD) 23 2.2.6.4 Polymeric Sizing Agents (PSA) 26 2.2.7 Determination of the Sizing Degree (Performance Analysis) 28 2.2.7.1 Cobb Water Absorption 29 2.2.7.2 Contact Angle Measurement 30 2.2.7.3 Penetration Dynamics Analysis 31 2.2.7.4 Further Qualitative Analysis Methods 33 2.2.7.4.1 Ink Stroke 33 2.2.7.4.2 Immersion Test 33 2.2.7.4.3 Floating Test 34 2.2.7.4.4 Hercules Sizing Tester (HST) 34 2.2.8 Sizing Agent Detection (Qualitative Analysis) and Determination of the Sizing Agent Content (Quantitative Analysis) 35 2.2.8.1 Destructive Methods 35 2.2.8.2 Non Destructive Methods 36 2.3 Alkenyl Succinic Anhydride (ASA) 36 2.3.1.1 Chemical Composition and Production of ASA 37 2.3.1.2 Mechanistic Reaction Models 39 2.3.1.3 ASA Application 42 2.3.1.3.1 Emulsification 42 2.3.1.3.2 Dosing 44 2.3.1.4 Mechanistic Steps of ASA Sizing 46 2.3.2 Physico-Chemical Aspects during ASA Sizing 48 2.3.2.1 Reaction Plausibility 48 2.3.2.1.1 Educt-Product Balance / Kinetics 48 2.3.2.1.2 Energetics 51 2.3.2.1.3 Sterics 52 2.3.2.2 Phenomena based on Sizing Agent Mobility 53 2.3.2.2.1 Sizing Agent Orientation 54 2.3.2.2.2 Intra-Molecular Orientation 55 2.3.2.2.3 Sizing Agent Agglomeration 55 2.3.2.2.4 Fugitive Sizing / Sizing Loss / Size Reversion 56 2.3.2.2.5 Sizing Agent Migration 58 2.3.2.2.6 Sizing Reactivation / Sizing Agent Reorientation 59 2.3.3 Causes for Interactions during ASA Sizing 60 2.3.3.1 Process Parameters 61 2.3.3.1.1 Temperature 61 2.3.3.1.2 pH-Value 62 2.3.3.1.3 Water Hardness 63 2.3.3.2 Fiber Types 64 2.3.3.3 Filler Types 65 2.3.3.4 Cationic Additives 66 2.3.3.5 Anionic Additives 67 2.3.3.6 Surface-Active Additives 68 2.4 Limitations of State-of-the-Art ASA-Sizing Analysis 69 2.5 Optical ASA Localization 71 2.5.1 General Background 71 2.5.2 Confocal Microscopy 72 2.5.2.1 Principle 72 2.5.2.2 Features, Advantage and Applicability for Paper-Component Analysis 74 2.5.3 Dying / Staining 75 3 Discussion of Results 77 3.1 Localization of ASA within the Sheet Structure 77 3.1.1 Choice of Dyes 77 3.1.1.1 Dye Type 78 3.1.1.2 Evaluation of Dye/ASA Mixtures 80 3.1.1.2.1 Maximum Soluble Dye Concentration 80 3.1.1.2.2 Thin Layer Chromatography 81 3.1.1.2.3 FTIR-Spectroscopy 82 3.1.1.3 Evaluation of the D-ASA Emulsion 84 3.1.1.4 Paper Chromatography with D-ASA & F-ASA Emulsions 85 3.1.1.5 Evaluation of the D-ASA Emulsion’s Sizing Efficiency 86 3.1.2 The Localization Method 87 3.1.2.1 The Correlation between ASA Distribution and Agglomeration 88 3.1.2.2 Measurement Settings 89 3.1.2.3 Manual Analysis 90 3.1.2.4 Automated Analysis 92 3.1.2.4.1 Automated Localization / Microscopy Measurement 92 3.1.2.4.2 Automated Analysis / Image-Processing 93 3.1.2.5 Result Interpretation and Example Results 96 3.1.2.6 Reproducibility 97 3.1.2.7 Sample Mapping 98 3.1.3 Approaches to Localization-Method Validation 102 3.1.3.1 Raman Spectroscopy 102 3.1.3.2 Confocal Laser Scanning Fluorescent Microscopy 102 3.1.3.3 Decolorization 103 3.2 Factors Impacting the Sizing Behavior of ASA 104 3.2.1 ASA Type 105 3.2.2 Emulsion Parameters 107 3.2.2.1 Hydrolyzed ASA Content 107 3.2.2.2 ASA/Starch Ratio 109 3.2.2.3 Emulsion Age 110 3.2.3 Stock Parameters 111 3.2.3.1 Long Fiber/Short Fiber Ratio 111 3.2.3.2 Furnish Type 112 3.2.3.3 Degree of Refining 114 3.2.3.4 Filler Type/Content 116 3.2.4 Process Parameters 119 3.2.4.1 Temperature 119 3.2.4.2 pH-Value 120 3.2.4.3 Conductivity 122 3.2.4.4 Water Hardness 123 3.2.4.5 Shear Rate 125 3.2.4.6 Dwell Time 127 3.2.4.7 Dosing Position & Dosing Order 128 3.2.4.8 Drying 130 3.2.4.9 Aging 131 3.3 Factors Impacting the Localization Behavior of ASA 132 3.3.1 Degree of Refining 132 3.3.2 Sheet Forming Conductivity 135 3.3.3 Water Hardness 136 3.3.4 Retention Aid (PAM) 137 3.3.5 Contact Curing 138 3.3.6 Accelerated Aging 139 3.4 Main Optimization Approach 141 3.4.1 Optimization of ASA Sizing Performance Characteristics 142 3.4.2 Emulsion Modification 144 3.4.2.1 Lab Trials / RDA Sheet Forming 146 3.4.2.2 TPM Trials 147 3.4.2.3 Industrial-Scale Trials 149 3.4.2.4 Correlation between Sizing Performance Optimization and Agglomeration Behavior on the Example of PAAE 152 3.5 Holistic Approach to Sizing Performance Explanation 154 4 Experimental Approach 157 4.1 Characterization of Methods, Measurements and Chemicals used for the Optical Localization-Analysis of ASA 157 4.1.1 Characterization of used Chemicals 157 4.1.1.1 Preparation of Dyed-ASA Solutions 157 4.1.1.2 Thin Layer Chromatography 157 4.1.1.3 Fourier Transformed Infrared Spectroscopy 157 4.1.1.4 Emulsification of ASA 158 4.1.1.5 Paper Chromatography 159 4.1.1.6 Particle Size Measurement 159 4.1.2 Optical Analysis of ASA Agglomerates 160 4.1.2.1 Microscopy 160 4.1.2.2 Automated Analysis 163 4.1.2.2.1 Adobe Photoshop 163 4.1.2.2.2 Adobe Illustrator 164 4.1.2.3 Confocal Laser Scanning Fluorescent Microscopy 166 4.2 Characterization of Used Standard Methods and Measurements 166 4.2.1 Stock and Paper Properties 166 4.2.1.1 Stock pH, Conductivity and Temperature Measurement 166 4.2.1.2 Dry Content / Consistency Measurement 167 4.2.1.3 Drainability (Schopper-Riegler) Measurement 167 4.2.1.4 Base Weight Measurement 168 4.2.1.5 Ultrasonic Penetration Measurement 168 4.2.1.6 Contact Angle Measurement 169 4.2.1.1 Cobb Measurement 169 4.2.1.2 Air Permeability Measurements 170 4.2.1.3 Tensile Strength Measurements 170 4.2.2 Preparation of Sample Sheets 171 4.2.2.1 Stock Preparation 171 4.2.2.2 Laboratory Refining (Valley Beater) 171 4.2.2.3 RDA Sheet Forming 171 4.2.2.4 Additive Dosing 173 4.2.2.5 Contact Curing 174 4.2.2.6 Hot Air Curing 174 4.2.2.7 Sample Aging 174 4.2.2.8 Preparation of Hydrolyzed ASA 175 4.2.2.9 Trial Paper Machine 175 4.2.2.10 Industrial-Scale Board Machine 177 4.3 Characterization of used Materials 178 4.3.1 Fibers 178 4.3.1.1 Reference Stock System 178 4.3.1.2 OCC Fibers 179 4.3.1.3 DIP Fibers 179 4.3.2 Fillers 180 4.3.3 Chemical Additives 180 4.3.3.1 ASA 180 4.3.3.2 Starches 181 4.3.3.3 Retention Aids 181 4.3.3.4 Poly Aluminum Compounds 181 4.3.3.5 Wet Strength Resin 181 4.3.4 Characterization of used Additives 182 4.3.4.1 Solids Content 182 4.4 Description of Implemented Advanced Data Analysis- and Visualization Methods 183 4.4.1 Design of Experiments (DOE183 4.4.2 Contour Plots 184 4.4.3 Box-Whisker Graphs 185 5 Conclusion 186 6 Outlook for Further Work 191 7 Bibliography 192 Appendix 207 7.1 Localization Method Reproducibility 207 7.2 DOE - Coefficient Lists 208 7.2.1 Trial 3.3.4 – Impact of Retention Aid (PAM) on Agglomeration Behavior and Sizing Performance 208 7.2.2 Trial 3.3.5 – Impact of Contact Curing on Agglomeration Behavior and Sizing Performance 208 7.2.3 Trial 3.3.6 – Impact of Accelerated Aging on Agglomeration Behavior and Sizing Performance 209

AbstractIn this chapter the fundamental principles of the interaction of poorly wetted particles with interfaces of particles and bubbles are investigated in a water-based model system in which the similarity of poor wettability of non-metallic inclusions by molten metal and the poor wettability of silanized metal-oxide-particles by water is utilized. Capillary forces, the presence of nanobubbles and absorption of gas layers accompany the decreased wettability and lead to strong attractive forces. The combined effect of wettability and surface roughness is analyzed in detail, employing a variety of Atomic Force Microscopy techniques, as well as theoretical modeling of capillary forces and retarded van der Waals Forces for layered substrates. These concepts are extended to investigate particle-bubble interactions at different approach velocities by Colloidal Probe Atomic Force Microscopy and analysis by the Stokes-Reynolds-Young–Laplace model. The influence of temperature effects on the particle–particle interaction is investigated by High Temperature Atomic Force Microscopy. Additionally, the suitability of different interaction potentials for the Molecular Dynamics simulation of sintering alumina nanoparticles is accessed. Macroscopic agglomeration and hetero-coagulation experiments in a baffled stirred tank provide an insight into the dynamics of agglomeration and hetero-coagulation at for the metal melt filtration typical inclusion concentrations and wettability states.

Colloids are defined as suspensions of finely divided particles in a continuous medium that do not settle rapidly and are not readily filtered. To be more specific, the International Union of Pure and Applied Chemistry defines a colloid as any material for which one or more of its three dimensions lies within the size range of 1 to 1000 nm. As the nucleation and growth of oxides from aqueous solutions almost always produces suspensions containing submicron particles (see Chapter 7), typical oxide suspensions fall squarely within the colloidal domain. In this book, we consider colloidal particles to represent oxides or hydroxides that are small enough to stay in aqueous suspensions for more than a few hours, yet are larger and lacking in the specific molecular structures of typical hydrolysis products (see Chapter 5). Given the density range of most oxides (from around 2−10 g/cm3), the sizes of most colloidal oxides fall within the limits of the International Union of Pure and Applied Chemistry (see Section 8.4.5). Colloidal oxide particles suspended in water represent a complex chemical environment. At the molecular level, protons, ions, small molecules, and polymeric species interact with particle surfaces to create charged surface sites and promote adsorption and desorption phenomena (see Chapter 6). These modified surfaces perturb the adjacent liquid, creating ordered solvent layers and strong concentration gradients in ions and other dissolved species. These interfacial phenomena generate a range of forces called interaction potentials. Such forces determine whether particles repel each other (leading to stable suspensions) or are attracted to one another, resulting in agglomeration and sedimentation phenomena. The length scales of those components of the oxide–water interface that influence the interaction potentials to be discussed in this chapter are introduced in Figure 8.1. At the subatomic level, the correlated polarization of electron clouds gives rise to dispersion forces described by quantum mechanics that contribute to van der Waals interactions. At the atomic level, the inherent charge on each exposed oxygen anion that terminates the oxide surface is controlled by local chemical bonds to adjacent cations (see Chapter 6).

Herein we addressed a study to determine the enhancement factor (EF) of the Raman signal reached by composite films with two main components, Ag nanoparticles and SiO2 spheres. The study involves the synthesis, structural composition and optical response by using experimental techniques and theoretical-numerical modeling. A colloid with single NPs and agglomerates of them, with a tannic acid layer on its surface, was produced. Separately, porous SiO2 spheres were obtained. A mixture of both, Ag NPs and SiO2 particles was used to produce the films by solvent evaporation method. It is shown that single or agglomerated Ag NPs are preferentially located at the interstices of the SiO2 spheres. Using discrete dipole approximation, the SERS EF has been estimated considering the agglomeration and tannic acid layer. Both, the dielectric spheres and tannic acid layer diminish the electric field intensity and therefore the SERS EF. When a Ag NP with/without a dielectric shell is touching a SiO2 sphere, the EF is as high as 1 × 103, the zones where this value is reached are smaller when the dielectric layer is present. With a cluster of 3 nude Ag NPs surrounded by SiO2 spheres an EF of 2.4 × 103 is obtained.

Recent studies have shown that addition of nano-sized particles to liquid fuels could significantly enhance major combustion characteristics such as burning rate and ignition delay. Colloidal suspensions are known to have enhanced optical properties and thermal conductivity compared to neat liquids; however, in the case of colloidal fuels, the main mechanism responsible for such enhanced properties is not well understood. To better understand these phenomena, colloidal suspensions of jet fuel and different types of carbon-based nanomaterials (carbon nanoparticles, multi-walled carbon nanotubes, and graphene nanoplatelets) prepared at different particle loadings were experimentally tested for their thermal conductivities. Colloidal suspensions of nanotubes showed higher conductivity compared to that of graphene and nanoparticle. This could justify higher burning rate of these fuels. Furthermore, and to differentiate between the effects of thermal conduction and radiation, droplet evaporations tests were carried out on colloidal suspensions of carbon nanoparticle under forced convection and in the absence of any radiation source. It was found that the presence of nanoparticle in jet fuel initially increases evaporation rate. However, a reduction in evaporation rate was observed at higher concentration as a result of particles agglomeration.

Silica, a predominant metal oxide and fundamental component of the Earth’s crust, exerts significant influence on diverse geochemical and industrial processes through its interactions with water. This study delves into the surface modification of bentonite clay, as a naturally occurring aluminosilicate source, via treatment with varied concentrations of Al(NO3)3, as a novel surface modification approach, and H2 SO4, as a control technique. The obtained results elucidated important alterations in micro-scale surface characteristics, colloidal stability, and rheological behaviour of the aqueous solutions derived from the modified bentonite samples. Zeta potential analyses showed shifts from a stable colloidal solution in untreated bentonite to heightened instability following aluminium nitrate (and acid) treatment(s). In addition, micro-scale surface analyses employing scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) and Fourier-transform infrared (FTIR) revealed significant changes, encompassing heightened degree of coagulation, caused by intensified neutralization, and diminished swelling capacities induced by surface modifications. EDS analysis validated cation exchange processes and intensified agglomeration with Al(NO3)3 treatment. Furthermore, the stability and rheological behaviour of resulting aqueous fluids demonstrated reduced stability in Al(NO3 )-treated samples, comparable to acid-treated samples, indicative of hydrophobic surfaces post-treatment. The findings highlighted the effectiveness of the applied treatment technique, emphasizing practical implications for surface-treated bentonite utilization in different environments. However, observed variations influenced by ion type and concentration prompt the imperative for further research to unveil specific mechanisms of treatment approaches on aluminosilicate systems. This endeavour contributes to advancing comprehension and optimization of silicate performance across diverse applications.

Abstract Suspensions of pure energetic nanomaterials in a liquid fuel, commonly termed as nanofuels, are desirable for their vastly different combustion properties compared to base fuels. Large scale, as well as lab scale, storage of such nanofuels is very challenging due to settling that occurs in these fuels over time. Various effects including high specific surface area (SSA) and high surface energy of nanoparticles facilitate nanomaterial agglomeration. The gradual agglomeration of the initially dispersed nanoparticles promotes their separation from the base fuel, followed by gravitational settling to the bottom due to the agglomerates growing in size. Reultrasonication of these stored colloidal suspensions has been taken to be the effective, and thus primarily employed, method to redisperse the settled nanomaterials in the base fuel. However, the settling behavior of these reultrasonicated samples can be significantly different from that of the initially prepared samples. This effect can introduce errors in determining important parameters such as burning rate, flame standoff ratio (FSR), and thus contributes to overall uncertainty in experimental results. To address this particular concern, the present research deploys a non-contact, non-invasive, quantitative, and simple experimental configuration to analyze suspension behavior. Soy Biodiesel, a promising renewable fuel was chosen as the base fuel and Acetylene Black was selected as the nanomaterial for the suspensions in this experimental study. Acetylene Black (AB) is both inexpensive and environmentally benign and has been previously employed as a carbon-based nanomaterial fuel additive. Surfactants are commonly used to help disperse nanomaterials, and they are included in this test protocol as well. To investigate the effect of such surfactants on the settling behavior, Span 80 (SP 80), a non-ionic surfactant with a Hydrophilic-lipophilic balance (HLB) value of 4.3, is tested and the effect of its concentration on the settling time of the samples is also recorded.

Magnetic fluids or ferrofluids are colloidal dispersions of magnetic nanoparticles in a liquid carrier. These nanoparticles have a specific size range in order to remain suspended in the liquid, about 3 to 15 nm. In this range Brownian motion (thermal molecular motion in the liquid) keeps the particles from settling out. Because magnetic particles tend to aggregate, and aggregates sediment faster than single particles, the particles are coated with a stabilizing dispersing agent. The surfactant must be matched to the carrier type and must overcome the attractive Van der Waals and magnetic forces between the particles to prevent agglomeration even when a strong magnetic field is applied to the ferrofluid. A device that can pump a fluid with no moving mechanical parts represents a very encouraging alternative since such device would be practically maintenance free. A magnetocaloric pump achieves this purpose by providing a pressure gradient to a ferrofluid placed inside a magnetic field while experiencing a temperature change. If the temperature change is produced by extracting heat out of an element that needs refrigeration, coupling this heat via a heat pipe with the magnetocaloric pump will result in a completely passive cooling system. For applications near ambient temperature the ferrofluid must have specific characteristics such as low Curie temperature, high pyromagnetic coefficient, high thermal conductivity and low viscosity. This work presents the detailed description of the synthesis of ferrofluids composed of Mn-Zn ferrite nanoparticles and the characterization of its magnetic and thermal properties. Different composition of Mn-Zn ferrites nanoparticles were produce and evaluated. This ferrite ferrofluid was compared with commercially available magnetite ferrofluid in a magnetocaloric pump prototype. Results of saturation magnetization, pyromagnetic coefficient, Curie temperature, particle size, viscosity and pressure increment inside the magnetocaloric pump are presented.

Abstract Hydrocarbons (oil and gas) contribute significantly to the total global energy requirement, thus, oil recovery improvement from the current reservoirs is key. Nanotechnology based enhanced oil recovery (EOR) is a potential technique that can considerably improve the oil recovery factor. However, complex reservoir fluids which are highly saline (specifically in offshore) affect the stability of nanofluids and limit their efficacy through pore blockage during flow through porous media and offer a reduction in oil recoveries. This study thus proposes a novel technique for nanofluid formulation using different additives and surface-active agents and investigated them for stability in different techniques. Moreover, the formulated nanofluid is then tested for EOR in sand-pack experiments. The sand-pack is fully saturated using a NaCl solution; providing a realistic high saline laboratory model during flooding similar to an offshore environment. Various studies involving the stability and viscosity of nanofluids, and efficiency for EOR for offshore reservoirs have been reported. The efficiency of the nanofluid systems for stability, rheologicalproperties, and EOR has also been compared with the conventional nanofluid and newly formulated nanofluid flood schemes. This study reports that the saline environment severely damage the nanofluid stability by reducing electrostatic repulsive forces (screening electrical charges of NPs), subsequently, quick settlement of NPs was observed. The agglomeration and sedimentation of NPs within the nanofluids generally reduces the cumulative oil production by permeability impairment. However, the inclusion of surface active agents (surfactant) re-establishes the physical stability of the surface coating mechanism which curtailed the effect of salinity, especially in offshore oilfields. The surface-coated NPs in the nanofluid enhanced stability for a prolonged duration by maintaining nanometer size which is crucial to avoid early particle aggregation thus demonstrating incremental oil recovery in offshore oilfield applications. This study discusses the novel fabrication methodology of stable nanofluids using colloidal aspects for offshore oilfield applications where formations salinity becomes a major challenge during flow through porous and permeable media.

The presence of considerable amounts of free charge dispersed in a liquid is the basis for electrokinetic phenomena which are related to the existence of an electrical double layer (EDL). In polar liquids, the dissociation of electrolytes into ionic species is well understood and numerous electrokinetic phenomena are known; a good overview is given by e.g. Delgado et al. [1]. In nonpolar liquids it is known that electrical charges can exist as well. The presence of these electrical charges is utilized, for example, in colloid science to stabilize particle suspensions [2]. For this purpose, surfactants are added which enhance the zeta potential of the particles in order to prevent their agglomeration. Additionally to the manipulation of surface charges, it is reported that the electrical conductivity of nonpolar liquids essentially increases when surfactant is added and traces of water are present [3]. Such ternary solutions of nonpolar liquid-water-surfactant are known to contain surfactant agglomerations, so-called inverted micelles with a size of several nanometers, detectable for instance by quasielastic lightscattering measurements. Figure 1 sketches the generation and structure of an inverted micelle. In general, surfactants are macromolecules consisting of different functional groups, e.g. a polar “head” and a nonpolar “tail”. Above the critical micelle concentration (cmc), surfactant molecules attach with their polar head at a water droplet forming the inverted micelle. It is assumed that electrical charges are dissolved in the polar core of the inversed micelles enabling opposite charges to be held sufficiently far apart and preventing an agglomeration of different micelles [4].

The outstanding properties of single-layer graphene sheets for energy storage are hindered as agglomeration or restacking leads to the formation of graphite. The implications of the aforementioned arise on the difficulties associated with the aqueous processing of graphene sheets: from large-scale production to its utilization in solvent-assisted techniques like spin coating or layer-by-layer deposition. To overcome this, aqueous dispersions of graphene were stabilized by cellulose nanocrystals colloids. Aqueous cellulose nanocrystals dispersion highlights as a low-cost and environmentally friendly stabilizer towards graphene large-scale processing. Colloids of cellulose nanocrystals are formed by electrostatic repulsion of fibrils due to de-protonated carboxyl or sulfate half-ester functional groups. Graphene dispersions are obtained by hydrothermal reduction of electrochemically exfoliated graphene oxide in the presence of cellulose nanocrystals. This approach allows the preservation of the intrinsic properties of the nano-sheets by promoting non-covalent interactions between cellulose and graphene. The dispersions could be cast to form free-standing flexible conducting films or freeze-dried to form foams and aerogels for capacitive energy storage.

Literature review of molten salt nanofluids is performed in this study with focus on the thermo-fluidic properties and performance in thermal management applications. The colloidal mixture of nanoparticles in a base liquid phase is called nanofluid. Molten salts such as alkali nitrate eutectics, alkali carbonate eutectics and alkali chloride eutectics have high melting temperatures. These materials are suitable for various high temperature applications, including as Heat Transfer Fluid (HTF), Thermal Energy Storage (TES), Concentrated Solar Power (CSP) plants, nuclear power, etc. The major drawback of molten salt materials is their low thermal conductivity and specific heat capacity. Enhancing the thermo-physical properties of molten salt materials can lower the cost of power production involving these materials (e.g., as HTF and/ or TES in CSP or nuclear power plants. Mixing molten alt eutectics with nanoparticles (e.g., molten salt nanofluids) can provide a cost-effective technique for enhancing the specific heat capacity and thermal conductivity which in turn can enable the reduction in the cost of power production. In this review - the following topics involving molten salt nanofluids were explored: thermo-physical property measurements, numerical modeling (e.g., Molecular Dynamics/ MD simulations), materials characterization (e.g., using electron microscopy techniques — such as SEM and TEM). For example, SEM studies in conjunction with MD simulation results confirm the formation of a dense layer of fluid molecules on the surface of nanoparticles that can enhance the specific heat capacity of these molten salt nanomaterials. Subsequently the concepts of nanofins was explored (which involves the study of interfacial thermal impedance, such as resistance, capacitance and diodicity). The contribution of these interfacial thermal impedances to the enhancement of specific heat capacity and thermal conductivity are also explored. Specific heat enhancement as high as 100% has been observed for various molten salt eutectics when doped with 1.5% (weight) silica nanoparticles. Various synthesis protocols such as one-step, two-step and three-step methods as well as conventional experimental methods used for specific heat capacity measurement are compared and examined. A review of the effects of concentration, nanoparticle size, temperature, base fluid, and nanofluid chemical properties is also performed. Other topics of interest are the anomalous enhancement of thermal conductivity in molten salt nanofluids which contradict typical predictions obtained from using the effective medium theory. The available data in literature shows enhancement in thermal conductivity by as much as 35–45% for carbonate eutectics doped with silica nanoparticles at 1% mass fraction. The possible mechanisms suggested for this improvement are briefly discussed and compared with experimental observations (e.g., using SEM). In addition, nanofluids often display non-Newtonian rheological behavior. This necessitates a rigorous study, since the applications of nanofluids will impact the required pumping power. Studies show that the rheological properties of molten salt nanofluids are a function of base salt composition, shape of nanoparticles selected, chemical formula of nanoparticles, concentration of nanoparticles, size of nanoparticles, temperature, shear rate and synthesis protocol of the nanofluid. Several models are introduced to predict the viscosity variation along with their advantageous and disadvantages. SEM results show agglomeration of nanoparticles can be reduced by doping the nanofluids with very small values of mass fractions of additives such as Gum Arabic.

Abstract Spray Systems are used very extensively in a wide range of industrial applications. Injection of liquid fuel in gasoline and diesel automotive engines, gas turbine aircraft and land-based engines, rocket engines and a wide variety of industrial furnaces and boilers, require improved control of atomization and spray characteristics to improve performance and efficiency and to reduce emission of pollutants to satisfy EPA regulations. Spray painting of automobiles, aircraft, bridges and a large range of manufactured products results in the waste of large proportions of paint that does not hit the target and is carried away by offspray, which requires expensive treatment to prevent pollution. In manufacturing processes, molten metal sprays are used for direct manufacture, using near net shaping, high temperature arc spray coatings (thermal spraying) and for coatings. The need to achieve uniform thickness film layers with low porosity, requires control of drop size, velocity, temperature and number density in the spray. More than 80% of agricultural crops are sprayed with herbicides, fungicides and insecticides, using aircraft and tractors. Drop size needs to be maintained sufficiently large during evaporation to prevent drift by wind away from the target crop. Drops that are too large cause wastage and low target transfer efficiencies. Control is required of initial drop size distributions and subsequent changes of spray characteristics from nozzle to target crops. Many industrial chemical and food processes use spray drying where liquid slurries, colloids and solutions are injected into heated gas (air) environments. Control of atomization and spray characteristics is required in order to meet the end product specifications, of particle size, agglomeration, porosity and friability. In the field of medicine, inhalation therapy is used for treatment of respiratory diseases. New developments include inhalation of cyclosporin to prevent rejection after lung transplants, deep lung inhalation of insulin as a more effective and comfortable treatment for diabetics and inhalation of chemotherapy for prevention of lung cancer for heavy smokers. The generation of monosize particles in nebulizers targeted to particular locations in the respiratory tract and lung surfaces requires accurate control of particle size and velocity during inhalation. Control of all these spray processes is achieved by improved atomizer design and accurate measurement of spray characteristics by phase Doppler, diffraction and imaging laser diagnostic instruments.