Download or read book Boundary Effects and Shear Thickening of Colloidal Suspensions A Study Based on Measurement of Suspension Microstructure written by M.Tharanga D. Perera and published by . This book was released on 2014 with total page 155 pages. Available in PDF, EPUB and Kindle. Book excerpt: The confocal microscopy technique also provides us with the advantage of measuring structure in real process flows. We have investigated how the microstructure evolves upstream and downstream in a porous medium. We notice more structure in a high volume fraction suspension and notice anisotropic behavior at regions where shear from the wall of the posts dominate. In other cases, a mixed flow behavior is observed due to collisions between pore surfaces and other particles resulting in a deviation from flow streamlines.
Download or read book Microstructure and Rheology of Concentrated Suspensions of Near Hard sphere Colloids written by Dennis P. Kalman and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The relationship between colloidal suspension microstructure and rheology is investigated to provide a solid understanding of the nonlinear rheology of concentrated suspensions, with a focus on shear thickening. These suspensions are also studied as a treatment to woven fabric in body-armor applications, where the insight from microstructural measurements is used to attempt to improve the application. The colloid and suspension properties are characterized via SEM, DLS, SANS, USANS, and rheometry. The rheology is mapped onto an effective hard-sphere model with the addition of a yield stress. An additional excluded volume shell, as measured by SANS and USANS structural measurements, accounts for interparticle interactions due to surface forces arising from the stabilizing layer on the particles. The microstructure of these near hard-sphere concentrated, shear-thickening colloidal dispersions are measured via SANS and USANS as a function of volume fraction, shear rate, and particle size. Special Rheo-SANS, flow-SANS, and flow-USANS instruments are developed and validated to measure microstructure in flowing systems. Structures measured via USANS show a cluster peak that arises from hydrocluster formation in concentrated, shear thickening suspensions. Structure measurements in SANS via 1-d averaged analysis and analysis of the 2-d structure corresponds to that expected from Stokesian Dynamics simulations. Micromechanics theory via a Stress-SANS law is used to calculate rheology from the microstructure for comparison. As the rheology calculated from the SANS data qualitatively agrees with that of the suspension and the structures seen correspond to those expected from simulations, strong confirmation of the hydrocluster mechanism for shear thickening is observed. This improved knowledge of the hydrocluster structure is used to develop an elastohydrodynamic theory for the limiting viscosity at high shear stresses due to particle deformations in the hydrocluster. Measurements of particle modulus give consistent application of this elastohydrodynamic model to suspensions studied in this thesis. In addition, the model is applied to widely varying suspensions, including those of hard mineral particles, polymer particles, microgels, and emulsions and consistent results are seen. The results of these fundamental studies of how particle size, concentration, and hardness affect suspension microstructure and rheology are used to engineer shear thickening fluid treated textiles, suitable for various types of protective devices.
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 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 The Effects of Particle Anisotropy on the Rheology and Microstructure of Concentrated Colloidal Suspensions Through the Shear Thickening Transition written by and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Though suspensions comprised of anisotropic particles are ubiquitous in industry, little has been done to elucidate the effects of particle anisotropy on concentrated suspension rheology, or the mechanism responsible for the reversible shear thickening observed in these systems. This dissertation explores the rheology and shear-induced microstructure of anisotropic particle suspensions through the shear thickening transition, and provides the first account of anisotropic particle alignment during shear thickening. For this investigation, Poly(ethylene glycol) (PEG)-based suspensions of acicular precipitated calcium carbonate (PCC) particles of varying particle aspect ratio (nominal L/D & sim; 2, 4, 7) are generated that demonstrate both continuous and discontinuous reversible shear thickening with increasing applied shear rate or stress. The critical volume fraction for the onset of discontinuous shear thickening decreases as the average particle aspect ratio is increased. However, the critical stress for shear thickening is found to be independent of particle anisotropy and volume fraction, and can be predicted based on the minor axis dimension of the particles in agreement with the critical stress scaling for hard-sphere suspensions. Small angle neutron scattering during shear flow (Rheo-SANS) demonstrates that long-axis particle alignment with the flow direction is maintained throughout the range of shear stresses investigated, including the shear thickening regimes for both continuous and discontinuous shear thickening PCC/PEG suspensions. Investigations of particle flow alignment following flow cessation provide evidence that the critical volume fraction for shear thickening may be associated with an isotropic-nematic transition within the anisotropic particle suspensions. Rheo-SANS investigations of concentrated kaolin clay suspensions demonstrate that disk-shaped particles exhibit particle alignment with the face surfaces orthogonal to the gradient direction during both continuous and discontinuous shear thickening. The critical stress at the onset of shear thickening for discontinuous shear thickening clay suspensions is observed to scale with the particle thickness dimension. The rheology and Rheo-SANS observations for both the acicular PCC and disk-like kaolin clay suspensions invalidate earlier hypothesis suggesting that shear thickening behavior in anisotropic particle dispersions results from increased particle rotations out of flow alignment potentially leading to particle jamming. Rather, the observations suggest that shear thickening in anisotropic particle suspensions is a consequence of short range hydrodynamic lubrication forces resulting in the formation of hydroclusters at higher shear rates, analogous to the behavior established for spherical particle suspensions. Lastly, anisotropic particle suspensions are used to successfully develop of shear thickening fluid (STF)/ballistic fabric composites. Shape anisotropy imparts the advantage of lower solids loading required to achieve energy dissipative improvements compared to spherical particle STFs. The observed improvements in ballistic and stab resistance response of these composites over that of ballistic fabrics alone suggests that they could potentially be used in the development of personal body armors with improved, multi-threat protective capabilities.
Download or read book Particle Interations in Concentrated Suspensions written by and published by . This book was released on 1993 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: An overview is presented of research that focuses on slow flows of suspensions in which colloidal and inertial effects are negligibly small. We describe nuclear magnetic resonance imaging experiments to quantitatively measure particle migration occurring in concentrated suspensions undergoing a flow with a nonuniform shear rate. These experiments address the issue of how the flow field affects the microstructure of suspensions. In order to understand the local viscosity in a suspension with such a flow-induced, spatially varying concentration, one must know how the viscosity of a homogeneous suspension depends on such variables as solids concentration and particle orientation. We suggest the technique of falling ball viscometry, using small balls, as a method to determine the effective viscosity of a suspension without affecting the original microstructure significantly. We also describe data from experiments in which the detailed fluctuations of a falling ball's velocity indicate the noncontinuum nature of the suspension and may lead to more insights into the effects of suspension microstructure on macroscopic properties. Finally, we briefly describe other experiments that can be performed in quiescent suspensions (in contrast to the use of conventional shear rotational viscometers) in order to learn more about boundary effects in concentrated suspensions.
Download or read book Flow and Microstructure of Dense Suspensions Volume 289 written by Leslie J. Struble and published by . This book was released on 1993-05-28 with total page 280 pages. Available in PDF, EPUB and Kindle. Book excerpt: The MRS Symposium Proceeding series is an internationally recognised reference suitable for researchers and practitioners.
Download or read book Product Design and Engineering written by Ulrich Bröckel and published by John Wiley & Sons. This book was released on 2013-08-02 with total page 367 pages. Available in PDF, EPUB and Kindle. Book excerpt: Covering the whole value chain - from product requirements and properties via process technologies and equipment to real-world applications - this reference represents a comprehensive overview of the topic. The editors and majority of the authors are members of the European Federation of Chemical Engineering, with backgrounds from academia as well as industry. Therefore, this multifaceted area is highlighted from different angles: essential physico-chemical background, latest measurement and prediction techniques, and numerous applications from cosmetic up to food industry. Recommended reading for process, pharma and chemical engineers, chemists in industry, and those working in the pharmaceutical, food, cosmetics, dyes and pigments industries.
Download or read book Confined Flow of Attractive Colloidal Suspensions written by Rahul Pandey and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Attractive particulate fluids flowing through complex confined geometries are frequently used in technological applications. While the flow properties of hard-sphere suspensions in micro-scale geometries have been studied extensively, the effects of interparticle attractions and particle size dispersity on the confined flow properties of particulate suspensions are not well understood. We used confocal microscopy, particle tracking, and bulk rheology to study the confined structure, dynamics, and flow properties of colloid-polymer mixtures, which serve as simple models of attractive particulate suspensions. We employed poly(methyl-methacrylate) spheres that were suspended in a refractive-index and density- matched solvent, and induced a controlled short-range depletion attraction between particles by adding non-absorbing linear polystyrene. First, we investigated the effects of particle size dispersity on confinement-induced solidification of colloid-polymer mixtures. We formulated mixtures of polymer and bidispersed colloids with particle size ratio aS/aL ≈ 0.49 at a constant total volume fraction fT and measured the dynamics of the large particles as a function of the volume fraction of large particles. The dynamics of large particles became slower as the volume fraction of large particles r=fL/fT was decreased or the confinement thickness was decreased, indicating increasingly solid-like behavior. Second, we investigated the effects of variation in particle size dispersity r on the rheology and microstructure of mixtures of polymer and bidispersed colloids. Significant changes in rheology and microstructure were observed only at high volume fractions of large particles. By contrast, dense suspensions fT = 0.40 were strong gels at all concentration of large particles and exhibited only modest rheological and microstructural changes. Finally, we investigated the effects of variation in interparticle attractions on the microchannel flow of colloid-polymer mixtures. In suspensions with weak interparticle attractions, the number density of particles increased downstream in the channel due to shear-induced migration and consolidation by compression. In suspensions with stronger interparticle attractions, an interconnected network of particles suppressed these mechanisms and prevented the increase in density downstream. Together, our results indicate that the confined structure, dynamics, and flow properties of attractive colloidal suspensions can be controllably tuned from fluid-like to solid-like by varying the interparticle attractions and the particle size dispersity.
Download or read book Chemical Abstracts written by and published by . This book was released on with total page 2762 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1989 with total page 410 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Complex Flow of Concentrated Suspensions written by Claire Forsyth and published by . This book was released on 2015 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis describes work done to investigate the effects of flow on concentrated suspensions. The work is largely about the effects of flow on concentrated colloidal suspensions, however, a short section on the effects of flow on concentrated granular suspensions is also given. Concentrated suspensions show a variety of complex flow behaviour. They can show Newtonian, shear thinning or shear thickening behaviour, depending on the applied stress or shear rate and concentration. The shear thickening behaviour may be discontinuous and this is characterised by a dramatic increase in viscosity above a certain threshold of stress. This is thought to be closely related to flow induced jamming, which can be defined as the conversion of a liquid system into a solid by imposed stress. This behaviour is not well understood and can cause significant complications in industry. It also has potential applications, for example in shock absorption. Due to their complexities and potential applications, gaining a better understanding of how shear thickening and jamming materials behave is of interest and forms the basis of this thesis. In this work, bespoke shear cells and a novel method to detect flow induced jamming were designed and utilised. This allowed jamming to be visualised and evaluated quantitatively. Conditions where jamming occurs were mapped out and the effects of parameters such as concentration, shear stress, system geometry and system confinement were investigated. This, and an analysis of jamming statistics, allowed ways to prevent and control jamming to be identified and a better understanding of the system to be achieved. Such an analysis is lacking in literature. The conditions where jamming was detected using the novel equipment matched well with measurements using a commercial rheometer. This supported the idea of discontinuous shear thickening and flow induced jamming being closely related. The studies allowed a mechanism for flow induced jamming and discontinuous shear thickening to be proposed. By designing and using novel equipment that is not commercially available, a better understanding of the effects of flow on concentrated suspensions was achieved. This could ultimately lead to a better understanding of complex flow systems and lead to more efficient processes.
Download or read book Journal of Rheology written by and published by . This book was released on 2006 with total page 412 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Rheology written by Christopher W. Macosko and published by VCH Publishers. This book was released on 1994 with total page 576 pages. Available in PDF, EPUB and Kindle. Book excerpt: Rheology: Principles, Measurements, and Applications will be of greatest interest to chemical engineers, chemists, polymer scientists, and mechanical engineers, as well as students in these and related fields.
Download or read book Shear Behavior and Microstructures of Confined Colloidal Suspensions written by John Eric Hug and published by . This book was released on 1995 with total page 662 pages. Available in PDF, EPUB and Kindle. Book excerpt: Rheological properties and microstructures of concentrated charge-stabilized suspensions confined to gap sizes on the order of a few particle diameters are investigated by molecular dynamics computer simulations. Suspensions of uniform spheres at volume fractions ranging from 0.28 to 0.53 covering the crystalline phase are studied. The suspensions are modeled as spheres interacting via a repulsive short-ranged electrostatic potential. Stress versus shear rate behavior is examined as a function of particle volume fraction, gap size, and shear history. Microstructures for systems at equilibrium and under shear are investigated by direct observation of particle configurations and by scattering patterns generated from structure factor calculations. The observed shear behavior and microstructures compare favorably with experimental shear studies of bulk colloidal suspensions. The shear response and stresses marking rheological transitions scale on the equilibrium modulus in a universal manner. Small changes in gap size result in significant differences in the equilibrium properties which in turn can affect the observed rheological response. Gap size also plays an important role at shear rates where catastrophic shear thinning and shear thickening occur. Qualitative differences in shear behavior between experiments and simulations are observed at high shear rates suggesting that particle interactions dominate the shear behavior at low shear rates and hydrodynamics becomes important at high shear rates.
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 Investigating Flow Behaviors of Colloidal Materials at the Single particle Scale written by Yen-Chih Lin and published by . This book was released on 2017 with total page 504 pages. Available in PDF, EPUB and Kindle. Book excerpt: My thesis work focuses on the nonlinear mechanical behaviors of colloidal suspensions at the particle-level. This work covers both quiescent and strongly sheared suspensions. For quiescent suspensions, we image their 3D structures with confocal microscopy, and implement Stress Assessment from Local Structural Anisotropy (SALSA) to visualize the stress fields in them. Unlike traditional numerical methods, SALSA takes a statistical approach converting the probability of hard-sphere Brownian collisions to stresses. This direct stress measurement allows us to quantify the particle-level stresses surrounding vacancies, dislocations, and grain boundaries in crystalline materials. To drive the suspensions away from equilibrium, we develop a confocal-rheoscope, which is able to shear and image colloidal materials simultaneously. Using this device, we investigate the nonlinear flow behavior governed by Brownian motion, shear induced diffusion, and advection, and more importantly, disentangle them. We also study particle assembly and its corresponding rheological properties under confinement. Finally, we study even more strongly sheared suspensions, in which particle dynamics are too fast to be imaged by a confocal microscope. Here, we use flow reversal rheometry to reveal the underlying mechanism of suspension shear thickening where the viscosity increases with shear rate. We show that the thickening behavior of a suspension arises from the particle contact forces rather than hydrodynamic interactions. Such findings then lead us to design a biaxial shear protocol that can tune the suspension viscosity on demand. This viscosity tuning capability is a foundational step toward using dense suspensions in 3D printing, energy storage, and robotics. ...
