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 Dispersion Stability Microstructure and Phase Transition of Anisotropic Nanodiscs written by Ravi Kumar Pujala and published by Springer. This book was released on 2014-06-03 with total page 161 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis explores the dispersion stability, microstructure and phase transitions involved in the nanoclay system. It describes the recently discovered formation of colloidal gels via two routes: the first is through phase separation and second is by equilibrium gelation and includes the first reported experimental observation of a system with high aspect ratio nanodiscs. The phase behavior of anisotropic nanodiscs of different aspect ratio in their individual and mixed states in aqueous and hydrophobic media is investigated. Distinct phase separation, equilibrium fluid and equilibrium gel phases are observed in nanoclay dispersions with extensive aging. The work then explores solution behavior, gelation kinetics, aging dynamics and temperature-induced ordering in the individual and mixed states of these discotic colloids. Anisotropic ordering dynamics induced by a water-air interface, waiting time and temperature in these dispersions were studied in great detail along with aggregation behavior of nanoplatelets in hydrophobic environment of alcohol solutions.

Download or read book Dynamic and Microstructural Response of Soft Colloidal Materials to Constant Stress Deformation written by Hubert Kenneth Chan and published by . This book was released on 2014 with total page 129 pages. Available in PDF, EPUB and Kindle. Book excerpt: Under low stress, soft disordered materials such as colloidal gels and glasses are kinetically-jammed, solid-like materials; as stress is increased, a transition to a liquid-like phase capable of steady flow is expected. This ability makes these materials attractive for personal care products, paints, foods, and other applications that require a material to exhibit distinct deformation behavior at different steps in its manufacturing or consumer use. However, the origins and implications of the solid-liquid transition are still often unclear, and insight into the conditions and mechanisms that govern this intricate rheology is imperative for the improvement and extension of numerous applications. In this dissertation, viscoelastic colloidal systems arrested through different routes are experimentally probed to uncover the determinants of their complex deformation behavior near the jamming transition. Results include the discovery that dilute, depletion-induced colloidal gels can yield via a two-step process, with proposed origins associated with interparticle bond rotation followed by bond rupture. Possible implications include an apparent anisotropic strengthening of the gel in response to applications of constant stress between the two yield points. Recognizing that complex rheological phenomena such as these can never be fully understood without insight into the microstructural and dynamic events that accompany them, a custom-built shear cell coupled to a confocal microscope is introduced for the direct visualization of constant stress deformation of soft materials. Included among its features is the ability to conduct measurements with dramatically reduced "creep ringing" than typically observed with commercial rheometers, attributable to its low moment of inertia and its unique torque generation mechanism. For the primary study in this dissertation, the shear cell is utilized to investigate the creep and flow behavior of repulsive and attractive colloidal glasses. With increasing stress, topological caging effects diminish, and dynamics become more spatially and temporally homogeneous. For creep deformation, each relaxation event occurs intermittently and involves many neighboring particles. During flow induced by large stresses, rearrangements are more frequent and require fewer cooperative particles. If interparticle attraction is introduced, significant displacements are prevented while interparticle bonds remain intact, and rearrangements require more cooperativity.

Download or read book Colloid Chemistry written by Clemens K. Weiss and published by MDPI. This book was released on 2019-01-15 with total page 233 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is a printed edition of the Special Issue "Colloid Chemistry" that was published in Gels

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 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 Colloid Process Engineering written by Matthias Kind and published by Springer. This book was released on 2015-04-22 with total page 397 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book deals with colloidal systems in technical processes and the influence of colloidal systems by technical processes. It explores how new measurement capabilities can offer the potential for a dynamic development of scientific and engineering, and examines the origin of colloidal systems and its use for new products. The future challenges to colloidal process engineering are the development of appropriate equipment and processes for the production and obtainment of multi-phase structures and energetic interactions in market-relevant quantities. The book explores the relevant processes and for controlled production and how they can be used across all scales.

Download or read book Encyclopedia of Complexity and Systems Science written by and published by Springer. This book was released on 2009-06-26 with total page 10398 pages. Available in PDF, EPUB and Kindle. Book excerpt: This encyclopedia provides an authoritative single source for understanding and applying the concepts of complexity theory together with the tools and measures for analyzing complex systems in all fields of science and engineering. It links fundamental concepts of mathematics and computational sciences to applications in the physical sciences, engineering, biomedicine, economics and the social sciences.

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 Theory and Applications of Colloidal Suspension Rheology written by Norman J. Wagner and published by Cambridge University Press. This book was released on 2021-04-15 with total page 438 pages. Available in PDF, EPUB and Kindle. Book excerpt: An essential text on practical application, theory and simulation, written by an international coalition of experts in the field and edited by the authors of Colloidal Suspension Rheology. This up-to-date work builds upon the prior work as a valuable guide to formulation and processing, as well as fundamental rheology of colloidal suspensions. Thematically, theory and simulation are connected to industrial application by consideration of colloidal interactions, particle properties, and suspension microstructure. Important classes of model suspensions including gels, glasses and soft particles are covered so as to develop a deeper understanding of industrial systems ranging from carbon black slurries, paints and coatings, asphalt, cement, and mine tailings, to natural suspensions such as biocolloids, protein solutions, and blood. Systematically presenting the established facts in this multidisciplinary field, this book is the perfect aid for academic researchers, graduate students, and industrial practitioners alike.

Download or read book Theory and Applications of Colloidal Suspension Rheology written by Norman J. Wagner and published by Cambridge University Press. This book was released on 2021-04-15 with total page 437 pages. Available in PDF, EPUB and Kindle. Book excerpt: Essential text on the practical application and theory of colloidal suspension rheology, written by an international coalition of experts.

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 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 The Structure Dynamics and Equilibrium Properties of Colloidal Systems written by David Bloor and published by Springer. This book was released on 1990-10-31 with total page 908 pages. Available in PDF, EPUB and Kindle. Book excerpt: Proceedings of the NATO Advanced Study Institute on Properties of Colloidal Systems, Aberystwyth, Wales, U.K., September 10-23, 1989

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 Colloids and the Depletion Interaction written by Henk N.W. Lekkerkerker and published by Springer Science & Business Media. This book was released on 2011-05-12 with total page 245 pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloids are submicron particles that are ubiquitous in nature (milk, clay, blood) and industrial products (paints, drilling fluids, food). In recent decades it has become clear that adding depletants such as polymers or small colloids to colloidal dispersions allows one to tune the interactions between the colloids and in this way control the stability, structure and rheological properties of colloidal dispersions. This book offers a concise introduction to the fundamentals of depletion effects and their influence on the phase behavior of colloidal dispersions. Throughout the book, conceptual explanations are accompanied by experimental and computer simulation results. From the review by Kurt Binder: "They have succeeded in writing a monograph that is a very well balanced compromise between a very pedagogic introduction, suitable for students and other newcomers, and reviews of the advanced research trends in the field. Thus each chapter contains many and up to date references, but in the initial sections of the chapters, there are suggested exercises which will help the interested reader to recapitulate the main points of the treatment and to deepen his understanding of the subject. Only elementary knowledge of statistical thermodynamics is needed as a background for understanding the derivations presented in this book; thus this text is suitable also for advanced teaching purposes, useful of courses which deal with the physics for soft condensed matter. There does not yet exist any other book with a similar scope..... The readability of this book is furthermore enhanced by a list of symbols, and index of keywords, and last not least by a large number of figures, including many pedagogic sketches which were specifically prepared for this book. Thus, this book promises to be very useful for students and related applied sciences alike." Eur. Phys. J. E (2015) 38: 73

Download or read book Journal of Rheology written by and published by . This book was released on 2008 with total page 932 pages. Available in PDF, EPUB and Kindle. Book excerpt: Includes abstracts from the Journal of the Society of Rheology, Japan.