Surfactants and Thickeners are both additives used in fully-formulated waterborne coatings to provide colloidal stability, thickening, and other functionality. The behavior of each ingredient in a coating must be understood and controlled to maintain colloidal stability as well as balance other desired properties of the liquid coating and the dry paint film. In this work, quaternary systems of Water-Latex-Thickener-Surfactant were investigated to further the understanding of their behavior in coatings. The thickener used was a well characterized, hydrophobically-modified, ethoxylated urethane (HEUR) with two C18 terminal hydrophobes and 795 average repeat units of ethylene oxide as the hydrophilic spacer. Two latexes, a hydrophobic butyl acrylate/styrene and a hydrophilic butyl acrylate/methyl methacrylate, each containing a small amount of methacrylic acid monomer were used. Six different surfactants, three non-ionic and three-anionic, were used. By maintaining the concentrations of latex and HEUR thickener as constants and varying the surfactant concentration, effects of the surfactant loading on rheology were determined. As concentration of surfactant increases, a characteristic shear-thickening maximum associated with bridging of latex particles by the HEUR thickener was seen to shift to higher shear rates; surfactants at all concentrations studied, except SDS, lowered the viscosities within the low shear rate region. Dynamic viscoelastic measurements shed further light into the behavior of the mixtures. The results will be explained based on surfactant and latex surface polarities and the competitive adsorption between the v surfactant and HEUR hydrophobes, and other interactions between surfactants and thickeners.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19234号 / 工博第4069号 / 新制||工||1628(附属図書館) / 32233 / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 渡辺 宏, 教授 古賀 毅, 教授 金谷 利治 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Micromechanics of solidluid interactions can play a key role controlling macro-scale engineering behavior of granular media. The main objective of this study is to numerically investigate the micromechanics involved in solidluid mixtures to develop a better understanding of the macroscopic behavior of granular media for different applications. This is accomplished by developing a numerical model coupling the Discrete Element Method (DEM) and the Lattice Boltzmann Method (LBM) and employing it to study three distinct yet interrelated applications throughout the course of this research. In the first application, the DEM model is used to provide a clear relationship between energy dissipated by micro-scale mechanisms versus the traditional engineering definition based on macro-scale (continuum) parameters to develop a better understanding for the frictional behavior of granular media. Macroscopic frictional behavior of granular materials is of great importance for studying several complex problems such as fault slip and landslides. In the second application, the DEM-LBM model is employed for studying the undrained condition of dense granular media. While the majority of previous modeling approaches did not realistically represent non-uniform strain conditions that exist in geomechanical problems, including the LBM in the proposed model offers a realistic approach to simulate the undrained condition since the fluid can locally conserve the system volume. For the third application, the DEM-LBM model is used to study discontinuous shear thickening in a dense solidluid suspension. Shear thickening in a fluid occurs when the viscosity of the fluid increases with increasing applied strain rate. The DEM-LBM results for discontinuous shear thickening were compared to experimental data and proved to be an accurate approach at reproducing this phenomenon. The validated DEM-LBM model is then used to develop a physics-based constitutive model for discontinuous shear thickening-shear thinning in granular medialuid suspension. A closedorm model is then calibrated using the DEM-LBM model and validated against existing experimental test results reported in the literature. Findings of this research demonstrate how micromechanical modeling can be employed to address challenging problems in granular media involving solidluid interaction.

Multi-phase fluid systems are an important concept in fluid mechanics, seen every day in how fluids interact with solids, gases, and other fluids in many industrial, medical, agricultural, and other regimes. In this thesis, the development of a two-dimensional digital microfluidic device is presented, followed by the development of a two-phase microfluidic diagnostic tool designed to simulate sandstone geometries in oil reservoirs. In both instances, it is possible to take advantage of the physics involved in multiphase flows to affect positive outcomes in both. In order to make an effective droplet-based digital microfluidic device, one must be able to precisely control a number of key processes including droplet positioning, motion, coalescence, mixing, and sorting. For planar or open microfluidic devices, many of these processes have yet to be demonstrated. A suitable platform for an open system is a superhydrophobic surface, as suface characteristics are critical. Great efforts have been spent over the last decade developing hydrophobic surfaces exhibiting very large contact angles with water, and which allow for high droplet mobility. We demonstrate that sanding Teflon can produce superhydrophobic surfaces with advancing contact angles of up to 151° and contact angle hysteresis of less than 4°. We use these surfaces to characterize droplet coalescence, mixing, motion, deflection, positioning, and sorting. This research culminates with the presentation of two digital microfluidic devices: a droplet reactor/analyzer and a droplet sorter. As global energy usage increases, maximizing oil recovery from known reserves becomes a crucial multiphase challenge in order to meet the rising demand. This thesis presents the development of a microfluidic sandstone platform capable of quickly and inexpensively testing the performance of fluids with different rheological properties on the recovery of oil. Specifically, these microfluidic devices are utilized to examine how shear-thinning, shear-thickening, and viscoelastic fluids affect oil recovery. This work begins by looking at oil displacement from a microfluidic sandstone device, then investigates small-scale oil recovery from a single pore, and finally investigates oil displacement from larger scale, more complex microfluidic sandstone devices of varying permeability. The results demonstrate that with careful fluid design, it is possible to outperform current commercial additives using the patent-pending fluid we developed. Furthermore, the resulting microfluidic sandstone devices can reduce the time and cost of developing and testing of current and new enhanced oil recovery fluids.

Les suspensions non browniennes présentent un comportement rhéologique très différent en fonction de leur concentration. L'écoulement de suspensions semi-diluées est newtonien et montre une migration des particules provoquant des hétérogénéités de concentration. Au contraire, les suspensions concentrées présentent un large éventail de phénomènes rhéologiques non linéaire. Ce travail cherche à mieux comprendre les écoulements de suspensions dans différente gamme de concentration. A basse concentration,une étude de la migration est réalisée afin de quantifier les forces responsables de ce phénomène. Pour cela, les forces de migration sont comparées aux forces de sédimentation,grâce à un écoulement unidirectionnel et confiné. Des techniques de suivi de particules avancées et la microscopie confocale, permettent une mesure systématiquement à la fois des profils de fraction volumique et des profils de vitesse. Plusieurs systèmes sont comparés afin de mettre en évidence que les forces hydrodynamiques jouent un rôle important dans la migration. La seconde partie de ce travail consiste à caractériser l'écoulement d'un système rhéoépaississant. Des techniques de rhéologie locale, tel que la vélocimétrie ultrasonore et la tomographie RX sont utilisées dans différentes cellules de Couette. Ces techniques permettent de mesurer les profils de fraction volumique et les profils de vitesse. Nous soulevons que les propriétés rhéologiques dépendent fortement du confinement et de la rugosité, et parfois, nous avons observé instabilités dues aux interfaces. / Flows of non-Brownian suspensions are present in different fields, and exhibitdifferent behavior in function of concentration. Flows of semi-dilute suspensions aremainly governed by the spatial repartition of the particles. At low Reynolds numbers,it is indeed generally non-uniform due to cross-stream migration towards low shearedregions of the flow. In this work we aim at testing the idea that interactions betweenparticles could also be involved in the shear induced migration phenomenon. In orderto quantify the strength of shear induced migration, we take advantage of horizontalflow of buoyant particles in slits, where viscous resuspension is in competitionwith buoyancy.Using advanced particle imaging velocimetrie techniques and confocalmicroscopy, we measure systematically both volume fraction and velocity profiles.We compare two systems with and without interaction and any different was found.Concentrated suspensions exhibit a wide range of non linear rheological phenomena.This work characterizes the local rheology of a continuous shear thickening. We areused ultrasonic rheology and tomography RX in Couette cell for measured the volumefraction profile and velocity profile. We report that the rheological properties dependstrongly of the confinement and roughness, and sometimes we observed instabilitiesdue to the interface.

Cette thèse vise à comprendre l’effet des dynamiques des micelles de copolymères sur leurs propriétés rhéologiques. En effet les copolymères amphiphiles peuvent s'auto-assembler dans l’eau pour former diverses microstructures micellaires sphériques, cylindriques ou lamellaires. Leur dynamique est un paramètre crucial pour définir leur spectre d’applications, en particulier dans le transport de médicaments et dans la synthèse de matériaux méso-structurés. Les micelles se structurent en continu: elles peuvent se former et se dissocier en monomères, se fusionner ou se fragmenter. Nous avons développé une méthode basée sur la fluorescence pour sonder directement les dynamiques micellaires collectives de fusion et de fission dans un bon nombre de copolymères triblocs de la famille PEO-PPO-PEO. Cette thèse se concentre sur l'étude des systèmes micellaires formés par des copolymères triblocs (tensioactifs non ioniques) et les tensioactifs cationiques à des concentrations et des températures où micelles sphériques et micelles cylindriques sont formées. De telles structures peuvent être formées spontanément lorsque le système est soumis à des conditions appropriées de concentration et de température ou à l'induction entre elles en ajoutant des sels inorganiques ou organiques, ou en appliquant des contraintes de cisaillement au système tensioactif/eau.La technique de diffusion de la lumière dynamique (DLS) a été utilisée pour évaluer la transition de la structure dans des solutions micellaires en changeant la température du système et de la structure du système correspondant à des conditions de concentration - température.Des expériences de relaxation de contraintes ont été effectuées où l’assouplissement temporaire de contrainte est mesuré après une déformation instantanée dans des solutions aqueuses de P103. Les temps de relaxation (ou taux) sont comparés avec ceux obtenus par diffusion de la lumière et de leur rapport à la taille des micelles est montré. La relaxation des contraintes présente le comportement de Maxwell. Les temps de relaxation ont montré la dépendance de la température avec des comportements caractéristiques des régimes de micelles sphériques et allongées respectivement.Dans ce travail, nous étudions également le système micellaire CTAnFB avec n la substitution de fluor en positions ortho (F: 2), meta (F: 3) et para (F: 4), à savoir les systèmes CTAortoFB/, CTAmetaFB/eau et CTAparaFB/eau à des concentrations diluées. Nous présentons aussi une étude de la dynamique de la simulation moléculaire de l'hydratation de tensioactifs ortho-, méta- et para-fluorobenzoate et son effet sur la formation de micelles.Nous avons étudié l'effet des contre-ions organiques hydrotropes, 2-, 3- et 4-fluorobenzoïque (2FB-, 3FB- et 4FB-, respectivement) sur le comportement d'épaississement par cisaillement de solutions aqueuses micellaires de micelles en forme de tige de leurs sels avec des cations de cétyltriméthylammonium (CTA2FB, CTA3FB et CTA4FB).Ce travail a contribué à la compréhension de la synergie entre la structure, la dynamique micellaire et la rhéologie dans cette famille de copolymère. / This thesis aims to understand the effect of the dynamics of copolymer micelles on their rheological properties. Indeed amphiphilic copolymers can self-assemble in water to form various micellar microstructures spherical, cylindrical or lamellar. Their dynamic is a critical parameter to define their range of applications, particularly in the transport of drugs and in the synthesis of mesostructured materials. Micelles are structured continuous: they can form and dissociate into monomers, merge or fragment. We have developed a method based on fluorescence to probe directly collective micellar dynamics of fusion and fission in a number of triblock copolymers of PEO -PPO -PEO family.This thesis focuses on the study of micellar systems formed by triblock copolymers (nonionic surfactants) and cationic surfactants at concentrations and temperatures where spherical micelles and rod like micelles are formed. Such structures may be formed spontaneously when the system is subjected to appropriate conditions of concentration and temperature or to the induction of these by adding inorganic or organic salts, or by applying shear stresses to the surfactant/water system.The technique of dynamic light scattering (DLS) was used to evaluate the transition of the structure in micellar solutions by changing the temperature and the structure of the system itself at given concentration - temperature conditions.Stress relaxation experiments were performed where temporary relaxation of stress is measured after a momentary deflection in aqueous solutions of P103. The relaxation times (or rate) are compared with those obtained by light scattering and their relation to the size of the micelles is shown. The stress relaxation presented a Maxwelian behavior. The relaxation times showed temperature dependence with characteristic behavior schemes for elongated and spherical micelles respectively.In this work, we also study the micellar system CTAnFB where “n” is substitution of fluorine in the ortho position (F:2) meta ( F:3) and para (F:4), namely CTAortoFB/water CTAmetaFB/water and CTAparaFB/water systems in diluted concentrations. We presented a study of molecular dynamics simulation of the hydration of ortho-, meta-, para- Fluorobenzoate surfactants and its effect on the formation of micelles.The effect of hydrotropes organic counterions , 2- , 3- and 4- fluorobenzoic acid (2FB-, 3FB- and 4FB-, respectively), the shear thickening behavior of aqueous micellar solutions of rod like micelles thereof salts with cations of cetyltrimethylammonium (CTA2FB, CTA3FB and CTA4FB ) were studied.This work has contributed to the understanding of the synergy between the structure, dynamics and rheology of micellar in this family of copolymer.

Nous étudions des suspensions concentrées de particules non-colloïdales de PVC. Ces suspensions, appelées plastisols, sont utilisées principalement pour la fabrication de revêtements de sols.Elles présentent notamment un phénomène de rhéoépaississement (hausse de la viscosité en cisaillant). Nous montrons que cela provient des forces de frottement entre particules. En effet, à l’aide d’un microscope à force atomique, nous sommes pour la 1ère fois capable de relier directement la contrainte macroscopique d’apparition du rhéo-épaississement à la contrainte microscopique d’apparition de la friction solide entre particules.Nous caractérisons la viscosité de la suspension jusqu’à 100 000 s-1 et nous observons qu’une plus grande polydispersité limite le rhéoépaississement. Les différences de contraintes normales N1 et N2 sont aussi mesurées. Par ailleurs, des mesures à l’aide de rayons X ou d’ultrasons ne montrent aucune migration de particules sous cisaillement.Nous montrons également que la géométrie a un fort impact sur l’écoulement de la suspension concentrée. Un entrefer plus petit provoque une baisse de la viscosité et retarde le rhéoépaississement. Une approche non-locale permet de rationaliser les résultats.La substitution de particules de PVC par des particules de CaCO3 modifie profondément la viscosité et la densité d’empilement maximum. Nous développons alors des modèles simples pour modéliser ces effets. En outre, nous mesurons l’impact sur la rhéologie d’un éventuel surfactant à la surface des particules.Nous avons pu finalement étudier des instabilités observées en étalant ces suspensions à haute vitesse. Une instabilité de surface est d’abord observée. A plus haute vitesse, un dépôt se forme en aval sur le couteau. Nous corrélons ces instabilités avec l’apparition de différences de contraintes normales. / Highly concentrated and non-colloidal suspensions consisting of micrometric PVC particles dispersed in a liquid phase, were studied. These suspensions, called plastisol, are mostly used in vinyl flooring manufacture.A key feature of these suspensions is shear-thickening, since viscosity greatly increases as a function of the applied shear rate. This phenomenon is explained as being related to frictional forces between particles. Indeed, using an Atomic Force Microscope, we were able, for the first time, to link the macroscopic stress, at which shear-thickening appears, with the microscopic stress needed to enter a frictional regime.We then characterize the suspension viscosity up to 100 000 s-1. We observed that shear thickening is lowered with a more polydisperse powder. Large normal stress differences N1 and N2 were also measured, along with shear thickening. In addition, using both X-ray radiography and ultrasound, no particle migration in the sheared suspension could be detected.We also found that geometry plays a major role in the features of the flow of concentrated suspensions. For a smaller gap, the viscosity is lower and shear-thickening is pushed to higher shear rates. A non-local approach accounts for our experimental results.Replacing a number of PVC particles with CaCO3 particles changes both the viscosity and the maximum packing fraction quite dramatically. For both of these, we developed simple models that matched quite well with the experimental data. Moreover, we elucidate the rheological changes resulting from adding surfactant at the surface of each particle type.Finally, we investigated some instabilities observed while coating at high speed. At a moderate speed, a ribbing phenomenon appears. At a higher speed, a deposit is formed on the knife (downstream). The appearance of these instabilities correlates with normal stress differences

<p><b>Part I: Micromechanics of dense suspensions</b></p><p>Particulate suspensions are ubiquitous in the industry & nature. Fresh concrete, uncured solid rocket fuel, & biomass slurries are typical industrial applications, while milk & blood are examples of naturally occurring suspensions. These suspensions exhibit many non-Newtonian properties like rate-dependent rheology & normal stresses. Other than volume fraction, particle material, inter-particle interactions determine the rheological behavior of suspension. The average inter-particle gaps between the neighboring particles decrease significantly as the suspension volume fraction approaches the maximum packing fraction in dense suspensions. So, in this regime, the short-ranged non-contact interactions are important. In addition, the particles come into contact due to asperities on their surfaces. The surface asperities are present even in the case of so-called smooth particles, as particles in real suspensions are not perfectly smooth. Hence, contact forces become one of the essential factors to determine the rheology of suspensions.</p><p> </p><p>Part I of this thesis investigates the effects of microscopic inter-particle interactions on the rheological properties of dense suspensions of non-Brownian particles by employing discrete particle simulations. We show that increasing the roughness size results in a rise in the viscosity & normal stress difference in the suspensions. Furthermore, we observe that the jamming volume fraction decreases with the particle roughness. Consequently, for suspensions close to jamming, increasing the asperity size reduces the critical shear rate for shear thickening (ST) transition, resulting in an early onset of discontinuous ST (DST, a sudden jump in the suspension viscosity) in terms of volume fraction, & enhances the strength of the ST effect. These findings are in excellent agreement with the recent experimental measurements & provide a deeper understanding of the experimental findings. Finally, we propose a constitutive model to quantify the effect of the roughness size on the rheology of dense ST suspensions to span the entire phase-plane. Thus, the constitutive model and the experimentally validated numerical framework proposed can guide experiments, where the particle surface roughness is tuned for manipulating the dense suspension rheology according to different applications. </p><p> </p><p>A typical dense non-Brownian particulate suspension exhibits shear thinning (decreasing viscosity) at a low shear rate followed by a Newtonian plateau (constant viscosity) at an intermediate shear rate values which transition to ST (increasing viscosity) beyond a critical shear rate value and finally, undergoes a second shear-thinning transition at an extremely high shear rate values. This part unifies & quantitatively reproduces all the disparate rate-dependent regimes & the corresponding transitions for a dense non-Brownian suspension with increasing shear rate. The inclusion of traditional hydrodynamic interactions, attractive/repulsive DLVO (Derjaguin and Landau, Verwey and Overbeek), contact interactions, & constant friction reproduce the initial thinning as well as the ST transition. However, to quantitatively capture the intermediate Newtonian plateau and the second thinning, an additional interaction of non-DLVO origin & a decreasing coefficient of friction, respectively, are essential; thus, providing the first explanation for the presence these regimes. Expressions utilized for various interactions and friction are determined from experimental measurements, resulting in an excellent quantitative agreement with previous experiments. </p><p><br></p><p><b>Part II: Motion in a stratified fluid</b></p><p>Density variations due to temperature or salinity greatly influence the dynamics of objects like particles, drops, and microorganisms in oceans. Density stratification hampers the vertical flow & substantially affects the sedimentation of an isolated object, the hydrodynamic interactions between a pair, and the collective behavior of suspensions in various ways depending on the relative magnitude of stratification inertia (advection), and viscous (diffusion) effects. This part investigates these effects and elicits the hydrodynamic mechanisms behind some commonly observed fluid-particle transport phenomena in oceans, like aggregation in horizontal layers. The physical understanding can help us better model these phenomena and, hence, predict their geophysical, engineering, ecological, and environmental implications. </p><p><br></p><p>We investigate the self-propulsion of an inertial swimmer in a linear density stratified fluid using the archetypal squirmer model, which self-propels by generating tangential surface waves. We quantify swimming speeds for pushers (propelled from the rear) and pullers (propelled from the front) by direct numerical solution. We find that increasing stratification reduces the swimming speeds of swimmers relative to their speeds in a homogeneous fluid while reducing their swimming efficiency. The increase in the buoyancy force experienced by these squirmers due to the trapping of lighter fluid in their respective recirculatory regions as they move in the heavier fluid is one of the reasons for this reduction. Stratification also stabilizes the flow around a puller, keeping it axisymmetric even at high inertia, thus leading to otherwise absent stability in a homogeneous fluid. On the contrary, a strong stratification leads to instability in the motion of pushers by making the flow around them unsteady 3D, which is otherwise steady axisymmetric in a homogeneous fluid. Data for the mixing efficiency generated by individual squirmers explain the trends observed in the mixing produced by a swarm of squirmers. </p><p><br></p><p>In addition, the ubiquitous vertical density stratification in aquatic environments significantly alters the swimmer interactions affecting their collective motion &consequently ecological and environmental impact. To this end, we numerically investigate the interactions between a pair of model swimming organisms with finite inertia in a linear density stratified fluid. Depending on the squirmer inertia and stratification, we observe that the squirmer interactions can be categorized as i) pullers getting trapped in circular loops, ii) pullers escaping each other with separating angle decreasing with increasing stratification, iii) pushers sticking to each other after the collision and deflecting away from the collision plane, iv) pushers escaping with an angle of separation increasing with stratification. Stratification also increases the contact time for squirmer pairs. The results presented can help understand the mechanisms behind the accumulation of planktonic organisms in horizontal layers in a stratified environment like oceans and lakes. </p><p><br></p><p>Much work has been done to understand the settling dynamics of spherical particles in a homogeneous and stratified fluid. However, the effects of shape anisotropy on the settling dynamics in a stratified fluid are not entirely understood. To this end, we perform numerical simulations for settling oblate and prolate spheroids in a stratified fluid. We find that both the oblate and prolate spheroids reorient to the edge-wise and partially edge-wise orientations, respectively, as they settle in a stratified fluid completely different from the steady-state broad-side on orientation observed in a homogeneous fluid. We observe that reorientation instabilities emerge when the velocity magnitude of the spheroids falls below a particular threshold. We also report the enhancement of the drag on the particle from stratification. The torque due to buoyancy effects tries to orient the spheroid in an edge-wise orientation, while the hydrodynamic torque tries to orient it to a broad-side orientation. The buoyancy torque dominates below the velocity threshold, resulting in reorientation instability.<br></p>

In day to day life we encounter many different materials which are intermediate between crystalline solids and simple liquids that include paints , glues , suspensions, polymers, surfactants, food and cosmetic products and so on. ‘Soft condensed matter’ is an emerging field of science that aims to generalize the flow and various deformation mechanisms in this apparent diverse class of materials from a ‘mesoscopic’ point of view (important length scales for these systems is usually 10nm-1μm) where the actual atomic and molecular details governed by various quantum mechanical laws are not very important. These soft systems are held together by weaken tropic forces and therefore can be perturbed easily (the typical elastic modulus of these materials is many orders of magnitude lower compared to metallic solids). Moreover, very long relaxation times in these systems(∼10−3 to 1 s) have made them ideal candidates to study non-equilibrium physics. The present Thesis is an endeavor to understand linear and non-linear flow behavior and low Reynolds number instabilities in various soft matter systems like suspensions of flocculated carbon nanotubes and carbon black, surfactant gels, colloidal glasses, Langmuir monolayers etc probed mainly by bulk and interfacial rheology, in-situ light scattering, particle image velocimetry(PIV) techniques and Fourier transform rheology. We also use dynamic light scattering techniques for particle sizing and characterization of Brownian systems. Chapter 1 gives a general introduction to soft condensed matter, particularly, the important length and time scales, various interactions and the rich phase behavior emerged from the delicate balance between energy and entropy in these systems. In this context, We describe the detailed phase behavior of two such systems studied in this thesis. We next describe briefly a few important concepts which motivate the main problems studied in the present thesis like the shear-thickening in suspensions of Brownian and non-Brownian particles, non-equilibrium steady state fluctuation relations in driven systems, elasticity driven instabilities in complex fluids, jamming transitions and aging behavior. This is followed by a discussion of the experimental techniques like linear and nonlinear rheology, including the Fourier transform rheology. Chapter 2 discusses the experimental techniques used by us in detail. We first describe the different components and mode of operations of the MCR-300 stress-controlled rheometer (Paar Physica, Germany) and various experimental geometries. Next we discuss the set up for two dimensional rheological measurements. The homebuilt imaging set up for in-situ polarized light scattering and direct imaging studies is described along with the in-situ particle image velocimetry (PIV) to map out the exact spatially resolved velocity profiles in 2D systems. We give a brief account of the techniques of Fourier transform rheology. At the end of this chapter, we briefly describe the angle resolved dynamic light scattering (DLS) set up (Brookhaven Instruments, USA). In Chapter 3, we study colossal discontinuous shear-thickening transition in confined suspensions of fractal clusters formed by multi-wall carbon nanotubes (MWNT) by rheology and in-situ imaging experiments. Monotonic decrease in viscosity with increasing shear stress, known as shear thinning, is a known rheological response to shear flow in complex fluids in general and for flocculated suspensions in particular. In the present experiments we demonstrate a discontinuous shear thickening transition where the viscosity jumps sharply above a critical shear stress by four to six orders of magnitude in flocculated suspensions of MWNT even at very low weight fractions(∼0.5%). Rheo-optical observations reveal the shear-thickened state as a percolated structure of MWNT flocs spanning the system size. We present a dynamic phase diagram of the non-Brownian MWNT dispersions revealing a starting jammed state followed by shear-thinning and shear-thickened states. The present study further suggests that the shear-thickened state obtained as a function of shear stress is likely to be a generic feature of fractal clusters under flow, albeit under confinement. An understanding of the shear thickening phenomena in confined geometries is pertinent for flow controlled fabrication techniques in enhancing the mechanical strength and transport properties of thin films and wires of nanostructured composites as well as in lubrication issues. We try to understand the flow of jammed and shear-thickened states under constant applied strain rate by studying the building up and relaxation of individual stress fluctuation events similar to the flow in dense granular materials. We also characterize the metastable shear thickened states by superposing a small sinusoidal stress component on a steady applied stress as well as by studying the a thermal entropy consuming fluctuations which are also observed for other jammed systems under an applied steady shear stress as described in the next chapter. Chapter 4 reports the study of non-equilibrium fluctuations in concentrated gels and glassy systems(in jammed state), the nature of fluctuations and their systemsize dependence in the framework of fluctuation relation and Generalized Gumbel distribution. In the first part, we show that the shear rate at a fixed shear stress in a micellar gel in a jammed state exhibits large fluctuations, showing positive and negative values, with the mean shear rate being positive. The resulting probability distribution functions (PDFs) of the global power flux to the system vary from Gaussian to non-Gaussian, depending on the driving stress and in all cases show similar symmetry properties as predicted by Gallavotti-Cohen steady state fluctuation relation. The fluctuation relation allows us to determine an effective temperature related to the structural constraints of the jammed state. We have measured the stress dependence of the effective temperature. Further, experiments reveal that the effective temperature and the standard deviation of the shear rate fluctuations increase with the decrease of the systemsize. In the second part of this chapter, we report a universal large deviation behavior of spatially averaged global injected power just before the rejuvenation of the jammed state formed by an aging suspension of laponite clay under an applied stress. The probability distribution function (PDF) of these entropy consuming strongly non-Gaussian fluctuations follow an universal large deviation functional form described by the Generalized Gumbel (GG) distribution like many other equilibrium and non-equilibrium systems with high degree of correlations but do not obey Gallavotti-Cohen Steady State Fluctuation Relation (SSFR). However, far from the unjamming transition (for smaller applied stresses) SSFR is satisfied for both Gaussian as well as non-Gaussian PDF. The observed slow variation of the mean shear rate with system size supports a recent theoretical prediction for observing GG distribution. We also establish the universality of the observations reported in this chapter in the light of other jammed systems under shear. We examine in the first part of Chapter 5, the shear-thinning behavior of a two dimensional yield stress bearing monolayer of sorbitan tristearate at air/water interface. The flow curve (stress vs shear rate) consists of a linear region at low shear stresses/shear rates, followed by a stress plateau at higher values. The velocity profile obtained from particle imaging velocimetry indicates that shear banding occurs showing coexistence of fluidized region near the rotor and solid region with vanishing shear-rate away from the rotor. In the fluidized region, the velocity profile which is linear at low shear rates becomes exponential at the onset of shear-thinning, followed by a time varying velocity profile in the plateau region. At low values of constant applied shear rates, the viscosity of the film increases with time, thus showing aging behavior like in soft glassy three-dimensional (3D) systems. Further, at the low values of the applied stress in the yield stress regime, the shear-rate fluctuations in time show both positive and negative values, similar to that observed in sheared 3D jammed systems. By carrying out a statistical analysis of these shear-rate fluctuations, we estimate the effective temperature of the soft glassy monolayer using the Galavatti-Cohen steady state fluctuation relation. In the second part of this chapter, we study in detail the non-linear viscoelastic behavior of Langmuir monolayers. Under oscillatory shear usually observed in many 3D metastable complex fluids with large structural relaxation times. At large strain amplitudes(γ), the storage modulus (G”) decreases monotonically whereas the loss modulus (G”) exhibits a peak above a critical strain amplitude before it decreases at higher strain amplitudes. The power law decay exponents of G” and G” are in the ratio 2:1. The peak in G” is absent at high temperatures and low concentration of sorbitan tristearate. Strain-rate frequency sweep measurements on the monolayers do indicate a strain-rate dependence of the structural relaxation time. The present study on sorbitan tristearate monolayers clearly indicates that the nonlinear viscoelastic behavior in 2D Langmuir monolayers is very general and exhibits many of the features observed in 3D complex fluids. We report in the first part of Chapter 6 scattering dichroism experiments to quantify the spatio-temporal nematodynamics of shear-thinning worm like micellar gels of surfactant Cetyltrimethylammonium Tosylate (CTAT) in the presence of salt sodium chloride (NaCl) enroute to rheochaos. For shear rates past the plateau onset, we observe a presence of alternating bright and dark‘ intertwined’ birefringent structures along the vorticity direction. The orientational order corresponding to these structures are predominantly oriented at +45deg and−45deg to the flow (v) in the (v,∇v) plane. The orientational dynamics of the nematics especially at the interface between the structures, has a one-to-one correspondence with the temporal behavior of the stress. Experiments show that the spatial motion of the vorticity structures depend on the gap thickness of the Couette cell. We next discuss the random temporal flow behavior of this system at high values of applied shear rate/stress in the framework of elastic turbulence in the second part of this chapter. Here, we study the statistical properties of spatially averaged global injected power fluctuations for the worm-like micellar system described above. At sufficiently high Weissenberg numbers (Wi) the shear rate and hence the injected power p(t) at a constant applied stress shows large irregular fluctuations in time. The nature of the probability distribution function (PDF) of p(t) and the power-law decay of its power spectrum are very similar to that observed in recent studies of elastic turbulence for polymer solutions. Remarkably, these non-Gaussian pdf scan be well described by an universal large deviation functional form given by the Generalized Gumbel (GG) distribution observed in the context of spatially averaged global measures in diverse classes of highly correlated systems. We show by in-situ rheology and polarized light scattering experiments that in the elastic turbulent regime the flow is spatially smooth but random in time, in agreement with a recent hypothesis for elastic turbulence. In Chapter 7, we study the vorticity banding under large amplitude oscillatory shear (LAOS) in a dilute worm-like micellar gel formed by surfactant CTAT by Fourier transform rheology and in-situ polarized light scattering. Under LAOS we found the signature of a non-trivial order-disorder transition of Taylor vortices. In the non-linear regime, higher harmonicde composition of the resulting stress signal reveals that the third harmonic I3 shows a very prominent maximum at the strain value where the number density (nv) of the Taylor vortices is maximum for a wide range of angular frequencies both above and below the linear crossover point. Subsequent increase in applied strain results in distortions of the vortices and a concomitant decrease in nv when I3 also drops very sharply and acts like an order parameter for this order-disorder transition. We further quantify the transition by defining an independent order parameter like quantity from the spatial correlation function of the scattered intensity and equivalently its Fourier transform which essentially captures the non monotonous third harmonic behavior. Lissajous plots indicate an intra-cycle strain hardening for the values of γ corresponding to the peak of I3 similar to that observed for hard-sphere glasses. Our study is an important step forward to correlating the structures developed in the system under LAOS to the appearances of the higher harmonics in the non-linear regime. The Thesis concludes with a summary of the main results and a brief account on the scope of future work as described in Chapter 8.