Download or read book Microscopic Characterization of Macroscopic Colloidal Gel Rheology written by Jae Hyung Cho (Scientist in mechanical engineering) and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: When attracted to one another, colloids, particles of size ranging from a few nanometers to a few microns suspended in a liquid, form a colloidal gel. The squishiness of a colloidal gel stems from its elastic space-spanning network of aggregated particles in a viscous liquid, which allows the gel to resist deformations like a solid under low stress, but to flow like a liquid under high stress. Owing to such mechanical versatility, colloidal gels are found in every corner of our lives as personal care products, dairy products, pharmaceuticals, and construction materials. Colloidal gels composed of functionalized particles are utilized for novel energy storage devices and biomedical applications. Engineering the mechanical behaviors of colloidal gels, however, remains a challenge due to our limited understanding of the link between microscopic particle interactions and macroscopic rheological properties. The state of thermodynamic nonequilibrium and the structural disorder of the network due to kinetic arrest of the attractive particles call for comprehensive investigation of colloidal gel rheology. In this thesis, we develop a better physical understanding of key rheological characteristics of a model colloidal gel via optical microscopy and rheometry. We employ differential dynamic microscopy to quantify the thermal fluctuations of the gel network across multiple length and timescales and rotational rheometry to characterize macroscopic strain and stress responses under shear. Use of the two complementary techniques enables us to show how the elasticity, the viscoelasticity, and the viscoplasticity of the gel on macroscopic scales arise from the microscopic structure and dynamics of the gel network while addressing different stages of the system from its gelation to yield or fluidization. Our findings suggest ways to systematically control the deformation and the flow of colloidal gels by tuning particle interactions or by adjusting external loadings.

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 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 Deuterium Nuclear Magnetic Resonance NMR and Rheology of Microgel Colloids at Ambient and High Pressure written by Suhad Adnan Sbeih and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Microgel colloids exhibit a polymer collapse transition resulting in a large reduction in colloid particle volume at high temperatures or pressures. They are of interest because of their potential for applications in areas, like drug delivery and chemical separation, that involve the uptake, encapsulation and release of small or biological molecules. The goal of this work is to obtain a microscopic understanding of the internal structure and microscopic dynamics of microgels by examining the temperature and pressure dependence of the collapse transition. Deuterium NMR (2H NMR) has been used to probe the microscopic dynamics of crosslinked poly N-isopropylacrylamide (polynipam) chains, in microgel colloids, as a function of temperature and pressure for a series of four crosslink densities (Cd). Each crosslinked microgel colloids was synthesized with deuteron labels on the nipam backbone (d3 nipam). Macroscopic properties of unlabeled colloids having the same crosslink densities were characterized by dynamic light scattering (DLS) and rheology. Rheological characterization as a function of temperature (T) and particle concentration (C), and for 4 crosslink densities, showed that the microgel viscosity decreases as temperature is increased. The Krieger- Dougherty model of the relative viscosity as a function of volume fraction was employed for viscosity analysis. The measured viscosity in the colloidal regime (at high T, low C) collapsed onto one line when plotted against volume fraction. This yields a measure of the water content in the particles as function of T. The water volume fraction in the microgel particle at 45OC was always found to be 0.6 for any Cd. 2H NMR spectra of the d3 nipam suspensions for all Cd indicated freely moving chains at low temperature and a nearly immobilized fraction above 35OC. This is consistent with DLS observations of a transition from swollen to collapsed colloids. Nipam segments in the collapsed phase of the d3 nipam suspension were more mobile than those in the dry powder. This suggests significant amounts of water in the collapsed phase, a finding consistent with the rheology observations. Variable pressure NMR (up to 90 MPa) showed a slight increase in transition temperature with pressure for all Cd values studied.

Download or read book Physical Gels from Biological and Synthetic Polymers written by Madeleine Djabourov and published by Cambridge University Press. This book was released on 2013-05-16 with total page 367 pages. Available in PDF, EPUB and Kindle. Book excerpt: Presenting a unique perspective on state-of-the-art physical gels, this interdisciplinary guide provides a complete, critical analysis of the field and highlights recent developments. It shows the interconnections between the key aspects of gels, from molecules and structure through to rheological and functional properties, with each chapter focusing on a different class of gel. There is also a final chapter covering innovative systems and applications, providing the information needed to understand current and future practical applications of gels in the pharmaceutical, agricultural, cosmetic, chemical and food industries. Many research teams are involved in the field of gels, including theoreticians, experimentalists and chemical engineers, but this interdisciplinary book collates and rationalises the many different points of view to provide a clear understanding of these complex systems for researchers and graduate students.

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 Linking the Macroscopic Rheological Properties of Gels to Micro and Nano scopic Colloidal Phenomena written by Peter B. Laxton and published by . This book was released on 2008 with total page 121 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Soft Glassy Rheology and Structure of Colloidal Gels written by Guangjun Yin and published by . This book was released on 2006 with total page 276 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effect of Particle Shape on the Structure and Rheology of Colloidal Suspensions and Gels written by Ali Mohraz and published by . This book was released on 2004 with total page 444 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 Development of a Model Colloidal System for Rheology Simulation written by and published by . This book was released on 2008 with total page 37 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of the experimental effort is to provide a model particle system that will enable modeling of the macroscopic rheology from the interfacial and environmental structure of the particles and solvent or melt as functions of applied shear and volume fraction of the solid particles. This chapter describes the choice of the model particle system, methods for synthesis and characterization, and results from characterization of colloidal dispersion, particle film formation, and the shear and oscillatory rheology in the system. Surface characterization of the grafted PDMS interface, dispersion characterization of the colloids, and rheological characterization of the dispersions as a function of volume fraction were conducted.

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 Analytical Characterization of Physical Properties of Colloidal Dispersions Gels written by Anita Khannikova and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The formation of colloidal dispersion gels (CDGs) by cross-linking partially hydrolyzed polyacrylamide polymers (i.e. HPAM 360 and HPAM 380) with aluminum (Al) citrate has been studied as a function of time and concentration of Al citrate using rheology, dynamic light scattering (DLS), and time-domain (low-field) nuclear magnetic resonance (NMR) measurements. This thesis shows that when HPAM 360 is cross-linked with Al citrate, the static and dynamic viscosities of the solutions increase with time and concentration of polymer and cross-linker. DLS analysis of HPAM 360 reveals structures that change over time, becoming more noticeable as Al citrate is increased. DLS and rheology results showed that that the mobility of water is constrained. This effect is more pronounced for higher concentrations of Al citrate, as well as longer aging time. In contrast to HPAM 360, varying the concentration of Al citrate added to HPAM 380 solutions did not result in viscosity changes over time, and NMR and DLS analyses did not provide a conclusive indication that structures other than a homogeneous polymer suspension were present in solution. It is concluded that HPAM 360 can form CDGs under specific experimental conditions, while the usefulness of HPAM 380 in this regard is unclear.

Download or read book Trends in Colloid and Interface Science XV written by Petros G. Koutsoukos and published by Springer. This book was released on 2003-07-01 with total page 309 pages. Available in PDF, EPUB and Kindle. Book excerpt: The 14th Conference of the European Colloid and Interface Society (ECIS 2000) was held in September 2000, in Patras, GREECE. Researchers from the academia and the industrial sector met and presented research work divided in nine thematic sections: molecular interactions in thin films, polymer-surfactant interactions, structure and dynamics at interfaces, biocolloids, colloids in pharmaceutical and biological applications, new trends in colloid and interface science techniques, rheology, self assembly of amphiphiles and measurements in concentrated suspensions. Selected contributions from these thematic areas are presented in the present volume and show the up today achievements of the Colloid and Interface Science.

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 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 Advances in Food Rheology and Its Applications written by Jasim Ahmed and published by Woodhead Publishing. This book was released on 2022-09-13 with total page 786 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advances in Food Rheology and Its Applications: Development in Food Rheology, Second Edition presents the latest advances in the measurement and application of food rheology, one of the most important tools for food companies when characterizing ingredients and final products, and a predictor of product performance and consumer acceptance. This second edition provides coverage of new rheological measurement techniques, including ultrasonic measurements of rheological properties of food and NMR approach, and precision in data handling, including coverage of mathematical modeling of rheological properties. As the range of food products has also broadened as a result of consumer demands and preference, this second edition includes a series of new chapters on dairy and plant-based foods. The amalgamation between food texture and sensory attributes will also be addressed. In addition, coverage of the correlation between rheological behavior and modeling of the fluid in a human stomach and food digestion will be assessed. A special focus has given on rheology of gel systems, including, food hydrogels, bigel and organogels. Written for food scientists, food technologists, sensory scientists, and others working in academia and industry, Advances in Food Rheology and Its Applications: Development in Food Rheology, Second Edition will be a welcomed and updated reference. - Considers the impact of artificial intelligence and machine vision on rheological characterization and process control - Presents ultrasonic measurements of rheological properties of food and NMR approach, and precision in data handling - Covers thermodynamic approach of rheology and interfacial rheology - Explains various gel systems rheology, including bogels and organogo gels