Download or read book Microstructure and Microrheology of Colloidal Gels written by Myung Han Lee and published by ProQuest. This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloidal gels are of considerable interest for both research and industry, within ceramic coatings, pharmaceutical formulations, and mineral recovery. External forces and fields, including shear deformation and gravitational sedimentation, lead to microstructural transitions, which depend on the nature and strength of interparticle interactions and on the connectedness and topology of the gel. Characterizations of the microstructure and its response to such perturbations enable us to understand and control the rheology of gels. In this dissertation, we report direct measurements of microscopic structure and mechanical response of gels with the ultimate aim of establishing fundamental relationships between the microstructure and rheological properties. We achieve this through the combined use of confocal microscopy and optical tweezers. First, we study the microscopic mechanical response of colloidal gels by manipulating single probe particles within the network. For this work, we use a refractive index and density matched suspension of polymethylmethacrylate (PMMA) particles with non-adsorbing polymer. As polymer concentration increases, a dynamically arrested, space-filling network is formed, exhibiting structural transitions from a cluster-like to a more homogeneous string-like gel phase. In a gel, probe particles are oscillated with an optical trap, creating the local strain field in the network. We find that the micromechanics correlate strongly with the gel structure. At high polymer concentration, strain fields scale as 1/ r to a distance quite close to the probe particle, as expected for a purely elastic material. In contrast, at low polymer concentrations, gels exhibit anomalous strain fields in the near-field; the strain plateaus, indicating that many particles move together with the probe. By rescaling the probe size in the theoretical model, we obtain a micromechanical gel correlation length, which is consistent with the structural difference in terms of "cluster-like" and "string-like". Next, we observe the gel elasticity and particle rearrangements in the same system. The gel microelasticity from Stokes equation monotonically increases with polymer concentration, corresponding to the aggregate internal stiffness. Then, we correct for the structural heterogeneity based on the micromechanical correlation length in gels using a prefactor suggested by Schweizer and coworkers. The revised elasticity is non-monotonically dependent on polymer concentration and is in better agreement with the bulk measurements. We also examine local elastic and plastic deformations in gels with the probe oscillation. The rearrangements strongly depend on the strength of attraction. Finally, we investigate the coupled aggregation and sedimentation phenomena of colloidal particles as functions of the strength of attraction and initial volume fraction. For this work, we use a refractive index matched and density mismatched suspension of fluorescent core-shell silica particles with a non-adsorbing polymer, polystyrene. Silica particles with a fluorescent core and non-fluorescent shell are synthesized using a modified Stober method in the presence of sodium dodecyl sulfate (SDS). For high gravitational Peclet numbers (Pe g>1), we find that the strong coupling between aggregation and sedimentation determines the growth of clusters and evolution of the suspension. Early in the aggregation process, the suspension structure depends on the attractive well depth and initial volume fraction with the functional form that resembles thermally activated barrier hopping processes in colloidal systems, such as the delayed sedimentation of gels. The aggregation behavior prior to sedimentation determines the final structure of the suspension. Finally, we find that compaction and rearrangements in the sediment correlate strongly with the depth of attraction, but not with the sediment structure. The results from this work are expected to provide a better understanding of the role of the local structure and particle interactions in micromechanics and rheology of gels. Such an understanding will ultimately lead to more accurate predictions and a better control of gel processing and properties.

Download or read book Controlling Microstructure and Rheological Properties of Colloidal Gels written by Gabriele Colombo and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Hydrodynamic Simulations of Colloidal Gels written by Michael Dean Bybee and published by ProQuest. This book was released on 2009 with total page 209 pages. Available in PDF, EPUB and Kindle. Book excerpt: BD simulations are also performed, and the results are compared with those of the FLD simulations. Remarkable agreement is observed for both the microstructure and dynamics, suggesting that the structural evolution and dynamics of colloidal suspensions with short-range attraction and long-range repulsion under quiescent conditions may not be very sensitive to the effects of hydrodynamic interactions.

Download or read book Microrheology of Responsive Hydrogels written by Travis Hope Larsen and published by ProQuest. This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Self-assembling hydrogels are an emerging class of materials that has received growing interest from the pharamaceutical and biomedical fields. Hydrogels have become exciting candidates for use in drug delivery and tissue engineering applications because of their unique combination of biological compatibility and responsive mechanical behavior. Successful engineering of these materials relies on establishing a relationship between the self-assembly mechanism, resulting microstructure, and final rheological properties. This dissertation focuses on passive microrheology to characterize transient and equilibrated structural and mechanical properties of self-assembling hydrogels. Passive microrheology uses the thermal motion of embedded, micrometerdiameter particles to locally probe the material and extract rheological and structural information. Microrheology compliments bulk rheology in studies of soft materials, with advantages that include exquisite sensitivity for low modulus materials, large frequency range, no applied external force, rapid data acquisition, and small required sample volumes. Characterization of the liquid-solid transition in hydrogelators relies on defining gelation properties such as the gel point and the critical scaling exponents. The gel point provides a reference by which to define gelation, while the critical scaling exponents offer insight into the nature of network interconnectivity. Using the principles of time-cure superposition and theoretical scaling relationships for near-critical gels, we develop a rigorous method for determining these values directly from microrheological measurements. A comprehensive analysis of localization error associated with video microscopy particle tracking microrheology validates our method and illustrates how the presence of error can either make time-cure superposition impossible or dramatically affect the values of the gel point and critical exponents. Heuristics are provided for minimizing sources of error to avoid potential misinterpretations of the results. We use time-cure superposition microrheology and our understanding of error to compare the gelation kinetics of four synthetic peptide hydrogelators that differ in sequence by a single point amino acid substitution. We study the effect of concentration, ionic strength, and temperature on the energetics of self-assembly and ultimately show that the gelation kinetics of the peptide hydrogelators can be predictably altered through peptide design when the forces that drive gelation are well understood. To provide a theoretical basis for the change in gelation kinetics with peptide sequence and total peptide charge, a simplified electrostatic double layer model is developed that accounts for intra- and intermolecular electrostatic interactions that occur during self-assembly. Interaction potentials are calculated and used to determine critical gel times, which agree semi-quantitatively with microrheology results. Finally, we utilize another passive microrheology technique, diffusing wave spectroscopy, to investigate the high-frequency viscoelastic response of self-assembling biopolymer hydrogels under nonequilibrium conditions. The addition of a network-activating motor protein and a network-crosslinking protein allows us to study the competitive mechanisms employed by cells to modify the rheology of their cytoplasmic environment. The observed response is shown to be dependent on the average distance between filament-bound motor proteins and the length-scale -dependent bending rigidity of the polymer filaments, with the transition between effective persistence lengths marked by a characteristic crossover length. For separation distances greater than the bare persistence length and below the crossover length, the response is dominated by transverse filament fluctuations, while at separation distances shorter than the persistence length and above the crossover length, the filaments are characterized by a reduced effective persistence length and higher effective temperature. Crosslinks are shown to recover the bare persistence length by reducing the length scale over which particle motion is sensitive to motor activity until it is smaller than the crossover length. Overall, this work expands the application of microrheology to characterize the gelation process and equilibrium properties of new and emerging selfassembling soft materials that are currently being engineered for future therapeutic applications.

Download or read book Microrheology and Microstructure of Poly vinyl Alcohol based Physical Gels written by Nan Yang and published by . This book was released on 2011 with total page 382 pages. Available in PDF, EPUB and Kindle. Book excerpt: We study the microrheology and microstructure of physically cross-linked poly(vinyl alcohol) (PVA) gels using atomic force microscopy, dynamic light scattering and particle tracking. We compare the microscopic rheological properties with the bulk properties measured using conventional shear rheometry, and correlate the rheological properties to the structure of the materials. We develop a new technique for investigating the viscoelastic properties of soft materials using the atomic force microscope. The electronic feedback of an atomic force microscope is modi ed by adding a small oscillatory voltage to the de ection signal, and the amplitude and phase of the motion of the sample stage is monitored by a lock-in ampli er to determine the viscous and elastic moduli of the sample. We apply this method to PVA hydrogels and suspended PVA nano bers. We find the moduli of both the bers and the hydrogels to show a signi cant frequency dependence. We perform rheological and dynamic light scattering measurements on PVA/poly(ethylene glycol) (PEG) blends during aging. The properties of the blends change much faster with age than those of the pure PVA solution, and the blends undergo phase separation and gel over time. From dynamic light scattering experiments, we observe changes of the relaxation times in the blends as they age. We determine the gel point on the microscopic scale from the depression of the intensity autocorrelation function of the scattered light. We nd that gelation of the PVA/PEG blends is induced by the growth of aggregates in the blends. By comparing the gel point determined by light scattering to that from the rheometry, we nd that the macroscopic gel point is earlier than the microscopic one, indicating that the gel transition is length-scale dependent. Particle tracking microrheology is used to investigate the microrheology and microstructure of these PVA/PEG blends as a function of PEG concentration and aging time. Dynamic light scattering probes the ensemble averaged motion of all tracer particles in the scattering volume, while particle tracking tracks the motion of many individual tracers. The local viscoelastic moduli are determined from the measurements using the generalized Stokes- Einstein relation. We nd that addition of PEG to the PVA solutions in uences the micro environment signi cantly, and that phase separation happens before gelation as the blends age. We again nd that the microscopic gel point occurs later than the macroscopic one, con rming the above results. The experimental results are consistent with a model in which the PVA/PEG blends consist of PVA-poor pores within a continuous PVA-rich domain which gels.

Download or read book Response of Dilute Colloidal Gels to Shear Deformation written by Bharath Rajaram and published by . This book was released on 2011 with total page 217 pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloidal gels are often subject to transient shear deformation during steps involved in their manufacturing, processing and handling. Understanding the microstructural and rheological implications of this deformation is of critical importance to a wide host of technologies that use these materials as feedstock, including the food processing and ceramic industries, and in emerging technologies such as direct write assembly. For these systems, the rheology and microstructural evolution are coupled by a circular interplay between the interparticle and hydrodynamic interactions at the micro- and nano- scale, and the macroscopically imposed stresses or strains making their predictions from theoretical models difficult. In this study, we directly probe the shear-induced evolution of the microstructure, dynamics and rheology of dilute, depletion-induced colloidal gels suspended in a refractive index- and density- matched solvent mixture. The real time response of the gel network to shear flow is quantified using a fast scanning confocal microscope coupled with a custom-built cone-and-plate shear cell. Our results capture, for the first time in real space, local dynamic and structural information during the gel's evolution to the applied shear. Broadly, the particle dynamics evolve through three prominent regimes: (i) a period of movement immediately following the imposition of shear, (ii) an intermediate interval characterized by a predominantly immobilized microstructure, albeit with sporadic local rearrangements and, (iii) a final regime consisting of disconnected clusters advecting along the shear flow direction with a plug-like flow profile. Here, the intermediate interval is associated with transient heterogeneities in the particle dynamics and the appearance of chain-like domains oriented along the extensional axis of the flow field. We also unveil a secondary yield point previously unforseen in such dilute systems. Remarkably, the onset of gel rupture is progressively delayed at positions closer to the center of the cone; the microstructural and rheological signatures of this behavior are interrogated and a unified theory accounting for hydrodynamic contributions is proposed. Finally, the terminal microstructure of the sheared gels is investigated by systematically varying the strength and range of the attractive interactions, and the rate of deformation, and the implications on the phase behavior of colloidal gels are discussed.

Download or read book Microstructure and Mechanical Properties of Colloidal Particle Gels written by Iwan Schenker and published by . This book was released on 2009 with total page 187 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Microstructural Dynamics of Colloidal Gels written by and published by . This book was released on 2020 with total page 154 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Flow induced Microstructural Evolution in Colloidal Particulate Gels written by Priya Varadan and published by . This book was released on 2002 with total page 322 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Improved Models of Colloidal Gels written by Zsigmond Varga (Ph. D.) and published by . This book was released on 2018 with total page 277 pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloidal gels, composed of sub-micron, mutually attractive particles that aggregate to form a system spanning network, are the most abundant and diverse soft matter in society with numerous familiar, yet also many exotic applications, ranging from common dairy products to novel medical implants. Despite this profusion, the link between network microstructure and macroscopic behavior and function remains a mystery. Computational models of the microstructural evolution of colloidal gels present one opportunity to efficiently study the emergence of bulk material properties. However, these simulations often fail to match experimental results and are unable to reproduce landmark observations set as benchmarks. This thesis is concerned with the systematic study of the influence of hydrodynamic interactions on colloidal gelation to explain the prevailing experimental-theoretical mismatch in the literature. The novel insights drive the development of improved models that can accurately describe the physics of colloidal gels. A series of computational studies carefully investigate the role of hydrodynamic interactions in determining the conditions for kinetic arrest of attractive dispersions. The collective dynamics enabled by fluid mechanics are shown to enhance coagulation leading to a shift in the gel boundary to lower strengths of attraction and lower particle concentrations when compared to models that neglect hydrodynamic forces. Simulations with long-ranged hydrodynamic interactions are found to faithfully reproduce experimental phase diagrams. This is shown to hold true both for purely attractive dispersions as well as in systems with repulsive barriers. Perturbation analysis is used to study the rheology of semi-dilute, attractive colloidal dispersions and it is demonstrated that both hydrodynamic interactions and the interparticle potential critically affect the viscoelasticity of the material. A normal mode analysis on colloidal gels is conducted using different models of the hydrodynamic interactions between suspended particles to investigate the relaxation rates and energy dissipation in the network. It is established that computational models neglecting long-ranged hydrodynamic interactions critically fail to compute accurate values of rheological properties of interest. These findings are then integrated to study experimentally observed instabilities of attractive dispersions under shear and during sedimentation. Models accounting for the prevalent hydrodynamic forces are used to demonstrate that the phenomena of vorticity alignment and log-rolling are fluid mechanical in origin. Experimental measurements of density fluctuations and shear anisotropy are accurately recovered in simulations for the first time. Finally, a theory is developed to quantitatively predict the collapse dynamics of freely settling colloidal gels and new engineering strategies for extending the process lifetime of gel networks are presented. The observations and results discussed in this thesis leave no doubt that the properties and the mechanical response of gels are fundamentally altered by many-body hydrodynamics. These will have to be properly accounted for in the first generation of predictive computational models employed in the engineering design of colloidal gels.

Download or read book Active Microrheology of Colloidal Suspensions written by Indira Sriram and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Typically, rheology is measured using bulk rheological techniques, which give information about the macroscopic properties of the fluid, such as viscosity, and elastic modulus. However, the recent advances in sensitive microscopic and optical techniques have led to the emergence of a new field, known as microrheology. Microrheological measurements are capable of resolving forces on the order of piconewtons, and can obtain very localized structural information in the test fluid. All microrheological techniques utilize embedded probe particles to determine the surrounding fluid properties. The most common form of microrheology is "passive" microrheology, wherein the probe particles execute purely Brownian or thermal motion. Alternatively, in "active" microrheology, probe particles are manipulated using an external source of force, such as laser tweezers or magnetic tweezers. Both techniques present specific advantages. Passive microrheology has been widely adopted because the design and implementation of experiments is relatively straightforward. However, since passive microrheology is constrained to rely on purely thermal motion, the recovered fluid behavior is always in a linear response regime. The goal of the present work is to adapt active microrheology to measure non-linear fluid properties such as shear thinning, and to determine the conditions where such measurements agree with bulk rheology. We begin by developing a small amplitude, oscillatory active microrheological technique, where a single probe particle is trapped and oscillated in a suspension of small bath particles, whose diameter that is approximately twenty times smaller than that of the probe diameter. The suspension microviscosity is recovered across a frequency range of 5-1000 Hz, and applied amplitudes which are approximately 10% of the probe diameter. We find that the suspension exhibits thinning behavior with increasing frequency. In addition, we obtain quantitative agreement between our microrheological measurements, drag microrheology measurements, and bulk rheology, suggesting that this technique is capable of recovering bulk viscosity values. Finally, we compare our results to a new theoretical model that accounts for the three sources of stress in active microrheological measurements of colloidal suspensions: (i) direct interactions between the probe and bath particles (ii) indirect interactions between bath particles, and (iii) Einstein stresses that arise from the particles' inability to shear in the same manner as the surrounding fluid. Notably, while indirect interactions and Einstein stresses are present in macroscopic techniques, direct interactions have no macroscopic analog. Therefore, if indirect interactions dominate in the measurements, the bulk suspension viscosity can be recovered. We find that indirect interactions dominate in the limit that the probe particle is far larger than the surrounding bath particles, and therefore determine both experimentally and analytically that our measurements recover the bulk suspension viscosity. Next, we analyze single probe drag measurements in a suspension of fluorescently labeled bath particles. We recover the suspension microviscosity, and directly correlate this to the microstructural deformation in the bath suspension. We find that the suspension exhibits thinning behavior as the velocity of the probe increases. In addition, the measured microviscosity is found to be in good agreement with recent computational studies in the "direct" collision limit, which is a measurement artifact when considering the bulk, non-linear response in a suspension. In addition, we find some departure between our experimental results, and recently performed theoretical studies, which we attribute to the presence of hydrodynamic interactions in our system. We further characterize the anisotropic, non-linear structures formed in the direct probe limit by performing two probe experiments in a colloidal suspension. We hypothesize that these structures could potentially lead to interprobe interactions. First, we hold two particles such that the line joining their centers is normal to the flow direction, and then conduct measurements as a function of probe velocity and interparticle separation. Both the drag force and microstructural deformation surrounding the particles are recovered. Intriguingly, we find that the microstructure induces a slight attraction between the probe particles, particularly at close separations, constituting a "non-equilibrium" depletion interaction. We then conduct two point measurements with the line joining the particles aligned parallel to the flow direction, and reexamine the forces on the probes, and the microstructural effects in the bath suspension. We find that the drag force experienced by both particles is the same, despite their orientation to the flow direction. In addition, we find several microstructural effects that differ from both the single probe and perpendicular case.

Download or read book Colloidal Suspension Rheology written by Jan Mewis and published by Cambridge University Press. This book was released on 2012 with total page 417 pages. Available in PDF, EPUB and Kindle. Book excerpt: Presented in an accessible and introductory manner, this is the first book devoted to the comprehensive study of colloidal suspensions.

Download or read book Interactions and Micromechanics of Colloidal Aggregates written by John Peter Pantina and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloidal gels exhibit rheological properties, such as yield stress and viscoelasticity, which arise from the manner in which stress is transmitted through the microstructure. Insight into the mechanisms of stress transmission is critical in developing a full understanding of the rheological properties of these materials. Paramount to this is a thorough knowledge of the interparticle interactions. To systematically study the influence of nanoscale particle interactions on gel elasticity and yield stress, we use multiple time-shared optical traps to direct the assembly of colloidal aggregates consisting of dozens of particles. This novel technique provides a direct method of measuring the micromechanical properties and near contact interactions of aggregates that mimic the gel backbone as a function of physicochemical conditions, such as the ionic strength, ionic species, and the presence of surfactant additives. We begin by measuring the response of chain aggregates composed of colloidal PMMA in adhesive contact, due to the presence of inorganic salts in solution, to an applied bending moment. The aggregates were found to exhibit an elastic response below a critical bending moment. The simplified geometry of the aggregate allows us determine the single-bond rigidity from the measured chain elasticity, which is then related to the work of adhesion, W SL, through the Johnson-Kendall-Roberts (JKR) theory of adhesion. Next, we study the effect surfactant additives have on the micromechanics of aggregates. It is observed that both the single-bond elasticity, and the critical bending moment decreases as the surfactant concentration increases. However, ionic surfactants do so more efficiently than non-ionic surfactants. This is a consequence of the greater particle surface charge that arises from the adsorption of ionic surfactants, which in turn results in a larger Columbic repulsion between the particles. Finally, we measure the interactions and micromechanics of colloidal particles confined to an oil-water interface. A very long ranged repulsion is initially observed between particles, in agreement with theoretical descriptions of an electrostatic dipole arising from a small number of dissociated charge groups on the particle surface in the oil phase. As the sample ages, however, the repulsion is found to decrease until the particles are capable of aggregating. The results from this work are expected to aid in the development of improved microrheological models of colloidal gels by providing better descriptions of the near-contact interactions between particles, as well as greater insight into the manner in which stress is transmitted through the gel backbone. These models will permit a greater degree of rational engineering to be incorporated into the development of colloidal gels for industrial applications. (Abstract shortened by UMI.).

Download or read book Understanding and Controlling the Microstructure of Complex Foods written by D. Julian McClements and published by Elsevier. This book was released on 2007-08-30 with total page 793 pages. Available in PDF, EPUB and Kindle. Book excerpt: It is widely accepted that the creation of novel foods or improvement of existing foods largely depends on a strong understanding and awareness of the intricate interrelationship between the nanoscopic, microscopic and macroscopic features of foods and their bulk physiochemical properties, sensory attributes and healthfulness. With its distinguished editor and array of international contributors, Understanding and controlling the microstructure of complex foods provides a review of current understanding of significant aspects of food structure and methods for its control.Part one focuses on the fundamental structural elements present in foods such as polysaccharides, proteins and fats and the forces which hold them together. Part two discusses novel analytical techniques which can provide information on the morphology and behaviour of food materials. Chapters cover atomic force microscopy, image analysis, scattering techniques and computer analysis. Chapters in part three examine how the principles of structural design can be employed to improve performance and functionality of foods. The final part of the book discusses how knowledge of structural and physicochemical properties can be implemented to improve properties of specific foods such as ice-cream, spreads, protein-based drinks, chocolate and bread dough.Understanding and controlling the microstructure of complex foods is an essential reference for industry professionals and scientists concerned with improving the performance of existing food products and inventing novel food products. - Reviews the current understanding of significant aspects of food structure and methods for its control - Focuses on the fundamental structural elements present in foods such as proteins and fats and the forces that hold them together - Discusses novel analytical techniques that provide information on the morphology and behaviour of food materials

Download or read book Aggregation and Gelation of Concentrated Colloidal Suspensions written by Sara Romer and published by Herbert Utz Verlag. This book was released on 2001 with total page 128 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Micromechanics and Rheology of Colloidal Gels Via Dynamic Simulation written by Lilian Challingsworth Johnson and published by . This book was released on 2018 with total page 554 pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloidal gels are soft solids comprising a viscoelastic, networked structure embedded in solvent. This network forms from microscopically small particles initially dispersed in a solvent which self-assemble into a hierarchical, space-spanning network of particles connected by physical bonds. When subjected to external forces, colloidal gels exhibit a solid-to-liquid transition yet regain elastic character when forcing is removed. Their tunable mechanical properties and ability to flow enable colloidal gels to serve as the foundation of a multitude of applications ranging from everyday products, like yogurt, to biomedical applications, such as injectable therapeutics. The nonlinear rheology of colloidal gels underlies their utility in nearly every application, for example, spreading, injecting, or pouring. The transition from rest to steady flow of colloidal gels is characterized by one or more stress overshoots indicative of gel yield. In strongly-bonded, dilute colloidal gels, yield is hypothesized to result from the catastrophic loss of the network structure. Solid-like fracture leading to fluidization of strongly bonded gels may not be relevant where particle strands are not single-particle thick chains but rather bicontinuous and time-evolving due to reversible bonds. The connections between gel yield and the structural evolution of dense, bicontinuous gels remains poorly understood due to the difficulty of imaging of the internal structure of dense particulate gels with sufficient time resolution in experiments and due to the large system size required in computational studies. Here we report large-scale dynamic simulation to study reversible colloidal gels to elucidate the micromechanical underpinnings of non-Newtonian behavior of soft materials and to understand ongoing phase separation. First, we show that the startup of a fixed strain rate reveals that colloidal gel yield, separating the short-time solid-like response from the long-time liquid-like response, can be framed as a transition in energy storage. Contrary to prior hypotheses connecting yield to loss of network connectivity, the network persists after flow startup and a predictive model connecting hierarchical structure to early-time stress growth is presented. We devised a novel approach to monitor bond stretching, compression, formation, and loss alongside macroscopic deformation. We find that changes in structure that underlie the stress growth and post-yield relaxation, as monitored by bond dynamics, indicate the switch from energy storage to release. After rheological yield, energy release continues if flow is sufficiently strong; however, when imposed flow is weak, energy release reverses after yield, and the gel densifies. This gives the important result that yield under weak flow can be viewed as a release from kinetic arrest, permitting the gel to evolve toward more complete phase separation. This supports our view that yield of weakly sheared gels is a `non-equilibrium phase transition'. Second, we compare our simulations to experimental measurements of colloidal gel rheology to study the influence of bond strength, volume fraction, and network morphology on the viscoelastic moduli. Strong agreement is found between linear viscoelasticity from sim...

Download or read book Flow Induced Microstructural Evolution of Thermoreversible Colloidal Gels of Adhesive Spheres written by Priya Varadan and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: