Computational Studies of the Rheological Properties of Anisotropic Colloids PDF Download
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Author: Christopher Ray Avins
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Author: Christopher Ray Avins
Publisher:
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Category :
Languages : en
Pages : 0
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Author: Vincent Labalette
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Colloidal clays are hydrous magnesium phyllosilicates (sometimes aluminum), usually bearing a negative structural charge coming from isomorphic substitution compensated by the presence of cations in the basal spacing or on the surface of the colloid. These nanoparticles have a platelet shape with an aspect ratio going from 20 to 100. When immersed in water, clays hydrate and swell, leading to the release of the cations. The hydroxyl group presents on the edge of the particles are sensitive to the pH (titrable sites) resulting in an amphoteric edge charge. At low pH the rim is positively charged and becomes neutral or negative at pH 11. Therefore, suspensions of colloidal clays have both charge and shape anisotropies. Thanks to these features, clay dispersions exhibit interesting optical properties (ochreous clays), mechanical properties (tile manufacturing, surface coating) and even cleaning properties (grease-removing). Although studied for decades, the behavior of colloidal clays remains controversial. In this manuscript, we propose a coarse-grained model to simulate particles with both structural and charge anisotropy. This model allows studying the behavior of colloidal suspensions at equilibrium and under shear flow. Contrary to the Monte-Carlo method usually employed to model the equilibrium behavior of anisotropic particles, the model presented in this thesis takes into account hydrodynamic interactions, allowing the dynamics of the system to be studied. The particles are coarse-grained as clusters of spheres bound by springs or constrained to a rigid body motion thanks to solid mechanics equations. The dynamics of the particles are computed using the Accelerated Stokesian Dynamics code (ASD), and the electrostatic interactions are computed in a pairwise additive fashion with a Yukawa potential. The implementation of this coarse-grained model in the ASD method allows studying the microstructure of anisotropic particles presenting similar features than Laponite, a 2:1 synthetic smectite clay widely studied experimentally and numerically in the literature. Several studies are presented here while varying the volume fraction and the range of electrostatic interactions. The dynamics of formation of the observed structures (Wigner glass, gel, overlapping coin, etc.) and their structural evolution behavior are then discussed. Finally, the rheological response of the different structures to a start-up shear has been studied, highlighting the importance of the ratio between the electrostatic and the hydrodynamic forces. For initially percolated systems, it has been shown that the stress response on the applied strain depends on the initial microstructure at short times, and exhibits shear-thinning and final viscous response independent of the initial structure.
Author: Safa Jamali
Publisher:
ISBN:
Category : Chemical engineering
Languages : en
Pages : 0
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Computational studies have emerged as a key class of scientific approached to solving different problems of interest in the past few decades. Dissipative Particle Dynamics, DPD, a mesoscale simulation technique based on Molecular Dynamics has been established as a powerful technique in recovering a wide range of physical and chemical processes. Nevertheless, absence of robust bridge between the computational parameters to the physical characteristics of a system has limited applications of DPD. Thus in the second chapter of this dissertation (after a brief introduction and organizational guideline in chapter 1) a systematic study will be presented, providing several routes for setting the simulation parameters based on the real experimental measures. Although computational and theoretical works have always been a crucial areas of research in the rheology society, DPD has not been employed in rheological studies. This is mainly due to the fact that a step-by-step guideline does not exist for rheological measurements in DPD. Another reason for this lack of success in rheological community is that the built-in thermostat in DPD is not capable of providing a stable control over the thermodynamics of the system under flow conditions. Thus, firstly in chapter 3 different methods of viscosity measurement and rheological studies will be discussed in detail, and consequently in chapter 4 a novel thermostat is presented to modify the natural shortcomings of DPD under flow. For decades now, scientists across different disciplines have attempted at identifying the nature of versatile rheological response of colloidal suspensions. Exhibiting Newtonian behavior at very low, shear-thinning at intermediate, and shear-thickening at high flow rates in dense colloidal suspensions exemplifies a broad range of rheological regimes within a simple solid-liquid system. Despite numerous experimental and computational efforts in explaining the underlying mechanism of these behavior, there is still an ongoing debate in the scientific community on the subject. Hence, in final chapter a comprehensive study on rheology of colloidal suspensions (including a complete flow curve, normal stress measurements and microstructural evolutions) is presented, based on the results and foundations in prior chapters as well as in the literature.
Author: Malgorzata Borowko
Publisher: CRC Press
ISBN: 0429524838
Category : Science
Languages : en
Pages : 625
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Book Description
This volume presents computer simulation methods and mathematical modelling of physical processes used in surface science research. It offers in-depth analysis of advanced theoretical approaches to behaviours of fluids in contact with porous, semiporous and nonporous solid surfaces. The book also explores interfacial systems for a wide variety of p
Author: John von Neumann-Institut für Computing
Publisher: Forschungszentrum Jülich
ISBN: 3893367586
Category :
Languages : en
Pages : 421
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Author: Robert G. Owens
Publisher: World Scientific Publishing Company
ISBN: 9781860941863
Category : Mathematics
Languages : en
Pages : 417
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Book Description
This work traces the development of numerical methods for non-Newtonian flows from the late 1960s to 2001. It begins with broad coverage of non-Newtonian fluids, including their mathematical modelling and analysis, and then specific computational techniques are discussed.
Author: Norman J. Wagner
Publisher: Cambridge University Press
ISBN: 1108423035
Category : Science
Languages : en
Pages : 437
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Book Description
Essential text on the practical application and theory of colloidal suspension rheology, written by an international coalition of experts.
Author: Jan Mewis
Publisher: Cambridge University Press
ISBN: 0521515998
Category : Science
Languages : en
Pages : 417
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Book Description
Presented in an accessible and introductory manner, this is the first book devoted to the comprehensive study of colloidal suspensions.
Author: Wolfgang E. Nagel
Publisher: Springer
ISBN: 331924633X
Category : Computers
Languages : en
Pages : 701
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Book Description
This book presents the state-of-the-art in supercomputer simulation. It includes the latest findings from leading researchers using systems from the High Performance Computing Center Stuttgart (HLRS) in 2015. The reports cover all fields of computational science and engineering ranging from CFD to computational physics and from chemistry to computer science with a special emphasis on industrially relevant applications. Presenting findings of one of Europe’s leading systems, this volume covers a wide variety of applications that deliver a high level of sustained performance. The book covers the main methods in high-performance computing. Its outstanding results in achieving the best performance for production codes are of particular interest for both scientists and engineers. The book comes with a wealth of color illustrations and tables of results.
Author: Martin Hoffmann
Publisher: Logos Verlag Berlin
ISBN: 9783832526818
Category :
Languages : en
Pages : 0
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Anisotropic colloids differ from isotropic particles as they may combine a non-spherical shape with a heterogeneous composition or surface chemistry. These versatile colloids have moved into the focus of various research groups in the fields of chemistry and physics. Hence, preparation pathways for novel model systems and their characterization are challenging aspects in fundamental research and material science. In the first part of this work, the author describes the synthesis and characterization of two colloidal systems with dumbbell-shaped core-shell morphology. The core consists of poly(methyl methacrylate) and poly(styrene). As a special feature, the attached shell layer promotes the change of the particle size and the aspect ratio by simply changing the ionic strength or temperature. Depolarized dynamic light scattering (DDLS) was used to investigate how these stimuli affect the translational and the rotational diffusion in the highly diluted state. The hydrodynamics of the particles could be well described with stick-boundary conditions by using analytical expressions for a double sphere, prolate ellipsoid and cylinder or the shell model, respectively. Electron and scanning force microscopy were applied to image the particle morphology in real space. The second part is devoted to the hydrodynamics of monodisperse, submicron-sized colloidal clusters, which consist of one to four spherical building blocks. The author demonstrates that the shell model is an excellent tool to identify the rotational relaxations which are accessible by DDLS.
