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 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 Microstructure Dynamics and Rheology of Model Soft Particulate Gels written by Minaspi Bantawa and published by . This book was released on 2021 with total page 488 pages. Available in PDF, EPUB and Kindle. Book excerpt: Soft particulate gels consist of a small amount of solid material (colloidal particles or small aggregates) embedded in a fluid and are industrially relevant materials for applications in a wide range of fields including foods, personal care products and, biomedicine. Due to attractive inter-particle interactions, the solid component self-assembles into an open, porous network which controls the overall mechanical response of the material. In this dissertation, I have studied a class of numerical models for particulate gels in which the particle contacts are described by an effective interaction combining a two-body attraction and a three-body angular repulsion. Using molecular dynamics, I have shown how varying the model parameters allows us to sample, for a given gelation protocol, a variety of gel morphologies. For a specific set of the model parameters, I have identified the local elastic structures that get interlocked in the gel network. Starting from the analytical expression of their elastic energy from the microscopic interactions, I have estimated their contribution to the emergent elasticity of the gel and gained a new insight into its origin. Using large scale simulations with Optimally Windowed Chirp (OWCh) signals, I have investigated the microscopic origin of the linear viscoelastic response of soft particulate gels. My results indicate that the viscoelastic spectrum of a wide range of gels, with different microstructures, is controlled by an underlying fractal characteristic of the gel network, i.e., its initial rigid backbone, and by the associated hierarchy of relaxation time scales.Building on these methods and analysis, I have also studied how the viscoelasticity of composite gels can be tuned by changing the nature of the interactions in different mixed components in close connection with experiments. In particular, I have shown how a significant increase of the elastic modulus in nanofiller composites can be achieved at unexpectedly low volume fractions of fillers when the interactions between the fillers and the gel matrix are attractive. Moreover, mixing components of different interaction strengths in a binary network can result in a non-monotonic dependence of modulus on composition, which can then be used to fine-tune the mechanical properties in novel gel materials. The architecture of the gel networks and properties such as bending stiffness of the gel strands embedded in soft gels and the prestress also enter non-linear properties such as strain-stiffening, yielding and failure, which I have studied especially in connection with experiments on biopolymer gel networks. My work supports the idea suggested by the experiments, that the linear and nonlinear moduli are controlled by both the network architecture and the fiber mechanics while the onset the nonlinear, stretch-dominated regime and the yield strain are controlled predominantly by the network architecture. The increased bending stiffness of gel strands finally together with prestress can result in a dramatic reduction of the bond-reforming capability after yielding, possibly leading to a more brittle mechanical failure. The stiffer gel strands, together with prestress, promote a more brittle failure.

Download or read book Microgel Suspensions written by Alberto Fernandez-Nieves and published by John Wiley & Sons. This book was released on 2011-01-11 with total page 475 pages. Available in PDF, EPUB and Kindle. Book excerpt: Providing a vital link between chemistry and physics on the nanoscale, this book offers concise coverage of the entire topic in five major sections, beginning with synthesis of microgel particles and continuing with their physical properties. The phase behavior and dynamics of resulting microgel suspensions feature in the third section, followed by their mechanical properties. It concludes with detailed accounts of numerous industrial, commercial and medical applications. Edited by David Weitz, Professor at Harvard and one of the world's pre-eminent experts in the field.

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 Microstructure and Mechanical Behavior of Concentrated Particle Gels written by Hans Markus Wyss and published by . This book was released on 2003 with total page 185 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Multiscale Probing of Colloidal Gelation Dynamics written by Jae Hyung Cho (S. M.) and published by . This book was released on 2018 with total page 71 pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloidal gels are viscoelastic materials characterized by the collective behavior of particles that form a space-spanning network. Although the network structure embodies the aggregation process of the particles, the kinetic pathway from a stable suspension to such a complex microstructure remains poorly understood. In this work, we explore the evolution of microscopic structure and dynamics of home-made colloidal particles in the early phase of gelation, by extending the applicability of Differential Dynamic Microscopy (DDM) to non-ergodic media. We demonstrate uncoupled development of the structure and dynamics that reveals an intermediate stage of gel formation, and compare the DDM results with the rheological features of evolving gels. We finally show how understanding the gelation at multiple length and time scales via DDM and rheology opens new ways to tune the mechanical properties of colloidal gels that bear inherent versatility.

Download or read book Theoretical and Applied Rheology written by P. Moldenaers and published by Elsevier. This book was released on 2013-10-22 with total page 1110 pages. Available in PDF, EPUB and Kindle. Book excerpt: More than 900 authors from over 35 countries contributed to the 1992 International Congress on Rheology. These proceedings volumes comprise 17 plenary and keynote papers, 250 oral contributions and some 200 poster presentations. All relevant aspects of rheology are covered, e.g., theoretical rheology, molecular theories, fluid mechanics, rheometry, experimental methods, foams, polymer solutions, polymer melts, rubber, solids, composites, biorheology, industrial rheology, polymer processing, food rheology and electrorheology, reflecting the development of rheology into a broad, multidisciplinary field of recognized academic and industrial relevance.

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 Gels Structures Properties and Functions written by Masayuki Tokita and published by Springer. This book was released on 2009-10-08 with total page 204 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume includes 28 contributions to the Toyoichi Tanaka Memorial Symposium on Gels which took place at Arcadia Ichigaya on September 10th-12th, 2008. The contributions from leading scientists cover a broad spectrum of topics concerning: Structure and Functional Properties of Gels - Swelling of Gels - Industrial and Biomedical Application. The symposium was held in the style of Faraday Discussions, which stimulated the active discussion. After the symposium, each manuscript was rewritten based on the discussion and the critical review. Since the research on gels is becoming more and more important both for academia and industry, this book will be an essential source of information.

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 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 Linking Single Particle Dynamics to Macroscopic Phenomena in Colloidal Gels written by Vijay Gopalakrishnan and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Gels Handbook written by Utkan Demirci and published by World Scientific Publishing Company. This book was released on 2016-01-09 with total page 1000 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hydrogels are made from a three-dimensional network of cross linked hydrophilic polymers or colloidal particles that contain a large fraction of water. In recent years, hydrogels have attracted significant attention for a variety of applications in biology and medicine. This has resulted in significant advances in the design and engineering of hydrogels to meet the needs of these applications. This handbook explores significant development of hydrogels from characterization and applications. Volume 1 covers state-of-art knowledge and techniques of fundamental aspects of hydrogel physics and chemistry with an eye on bioengineering applications. Volume 2 explores the use of hydrogels in the interdisciplinary field of tissue engineering. Lastly volume 3 focuses on two important aspects of hydrogels, that is, drug delivery and biosensing. Contains 50 colour pages.

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 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 System of Measuring Mechanical Properties of Colloidal Gels with Optical Tweezers written by Na Wang and published by . This book was released on 2006 with total page 112 pages. Available in PDF, EPUB and Kindle. Book excerpt: "We successfully assembled the main instrument, a time-sharing single beam optical tweezers, and calibrated the lateral stiffness of the optical trap. Our optical tweezers setup is used to study the polystyrene gel and it has many more applications in colloidal samples. The strong 3D optical trapping highlights the optical tweezers as a powerful technique suitable for further investigation of colloidal samples." --