Download or read book Dynamics and Non equilibrium Structure of Colloidal Dumbbell shaped Particles in Dense Suspensions written by Nils Heptner and published by . This book was released on 2016 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Structure and Dynamics of Equilibrium and Non equilibrium Systems written by Christoph Lutz and published by . This book was released on 2005 with total page 128 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Colloids in Non equilibrium Dynamical Density Functional Theory of Colloidal Suspensions Under External Forcing written by Urs Zimmermann and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Properties of Non equilibrium States written by Matthias Helmut Günter Krüger and published by . This book was released on 2009 with total page 135 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 A New Paradigm for the Colloidal Glass Transition written by Jialun Wang and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Molecular theories have been successfully adapted to predict phase separation and crystallization in colloidal dispersions and other complex fluids, resulting in powerful tools for engineering industrial materials. However, sometimes the liquid-to-solid transition in colloids occurs without crystallization, leading to formation of a solid with amorphous structure -- a colloidal glass. The ability to model and predict the colloidal glass transition is a broadly impactful problem both scientifically and industrially: vitrification plays a role in bacterial fitness, geophysical dynamics, and is central to industrial coatings, food processing, and materials engineering. But as with molecular glasses, attempts to adapt equilibrium theories to describe and predict the colloidal glass transition have met with limited success. Prior approaches to describing the colloidal glass transition typically involve adapting equilibrium models of free energy minimization or particle momentum balances. Some of the most notable efforts to describe the glass transition as a thermodynamic process aim to replace the second-order discontinuous transition that is emblematic of equilibrium transitions, supplanting it with a continuous but divergent growth in some operational length scale as the system freezes. The consensus view holds that this divergent growth in length scale produces divergent growth in relaxation time scale, which is a satisfying idea for a solidification process. However, this consensus view has recently been called into question by reports of non-diverging relaxation time at the glass transition. Rebuttals to such reports of finite relaxation point to other modes of relaxation in very dense suspensions, such as compressibility or deformability of particles. While elastic deformation gives a fair explanation for finite relaxation, our investigation reveals a fundamental flaw in reports of divergent growth of relaxation time in the putative glass region: widespread use (in theory and experiment) of {\em ad hoc} fitting equations that assume {\em a priori} a divergent growth of relaxation time. That is, divergent growth is enforced rather than predicted. In addition, the fits are agnostic to rate process and thus provide little mechanistic insight into how crystallization is bypassed or how relaxation and glassy aging occurs. The assumption of divergence grows out of a practical challenge faced in the study of colloidal glasses, namely the difficulty of preparing hard-sphere samples at sufficiently high volume fraction near to and beyond the putative glass transition. In the present work we utilize large-scale simulations of the dynamics of hard-sphere colloids to vitrify a suspension deep into the glass, overcoming the preparation limitations of experiments. Our approach is to trigger the glass transition via concentration quenches using a novel particle-size increase algorithm, at fixed system volume and macroscopic number density. Our method provides access to the detailed particle-scale dynamics that underpin glassy relaxation and colloidal phase behavior, which we track as the glass ages following the quench. This method provides a fundamental model scenario for triggering solidification of a colloidal fluid, by increasing the concentration of a suspension of hard spheres without the complicating effects of flow or of attractive forces, porosity, or softness that add their own contributions to energy storage and dissipation. The positions, velocities and suspension stress are tracked during and following each jump, and utilized to compute diffusion and osmotic pressure, relaxation time, and structural changes. The impact of quench depth and aging on dynamics and microstructural rearrangement are explored. We first test whether the dynamics of a glassy system follow a universal scaling law in volume fraction via time-concentration superposition, a colloidal analog of the time-temperature superposition in molecular systems. While the alpha (slow) relaxation curves can be superimposed across temperatures, and separately, the beta (fast) relaxation curves can be superimposed, the response cannot be superimposed across all time scales. The fact that the time-concentration superposition holds only within well-separated time scales suggests that the two regimes are governed by distinct mechanisms. This finding further indicated that even though, deep into the glass, some relaxation processes slowed markedly, fast dynamics persist. This led us to more detailed study of dynamics near to the glass transition. We systematically quenched a suspension of hard spheres from the liquid into varying depths near and into the putative glass, and performed a detailed study of particle-scale dynamics. We found that both long- and short- time particle dynamics persist, even in ultra-dense systems. Study of structure and cooperative motion revealed that, contrary to prior consensus, relaxation in the glass occurs via self-motion rather than cooperative motion. We show that self-motion of particles enables relaxation of a surrounding glassy cage, where a tracer then undergoes long-time self-diffusion. However, the long-time self-diffusion occurs over a very short length scale, which shrinks with colloidal concentration (as opposed to diverging length scales of prior models). This self-diffusion relaxes the glass into an intransient diffusive state. We call this relaxation mechanism "dense diffusion", the exploration of a dense local configuration space that permits sampling of many configurations via local particle motion. Finally, we present evidence of a driving force for the dense diffusion, using structural and osmotic pressure measurements. The structural relaxation is illustrated as a smoothing process of locally sharp concentration gradient generated by the fast concentration quenches, where osmotic pressure drives this relaxation. Overall, this work reveals a new micro-mechanical perspective of the colloidal glass transition, where the system exhibits a smooth transition in relaxation mechanisms without being completely "frozen" at a divergent relaxation time. Our findings may be particularly useful in advancing designs of soft-solid materials and deepening our understanding of biological processes.

Download or read book Self assembly and Dynamics of Colloidal Dispersions in Steady and Time varying External Fields written by Zachary Michael Sherman and published by . This book was released on 2019 with total page 199 pages. Available in PDF, EPUB and Kindle. Book excerpt: A diverse set of functional materials can be fabricated using dispersions of colloids and nanoparticles. If the dispersion is responsive to an external field, like dielectric and charged particles in an electric field or paramagnetic particles in a magnetic field, the field can be used to facilitate self-assembly and control particle transport. One promising feature of field-responsive materials is the ability to drive them out of equilibrium by varying the external field in time. Without the constraints of equilibrium thermodynamics, out-of-equilibrium dispersions display a rich array of self-assembled states with useful material and transport properties. To leverage their unique behaviors in real applications, a predictive, theoretical framework is needed to guide experimental design. In this thesis, I carry out a systematic investigation of the self-assembly and dynamics of colloidal dispersions in time-varying external fields using computer simulations, equilibrium and nonequilibrium thermodynamics, and electro-/magnetokinetic theory. I first develop efficient computational models for simulating suspensions of polarizable colloids in external fields. The simulations are accurate enough to quantitatively reproduce experiments but fast enough to reach the large length and time scales relevant for self-assembly. I use this simulation method to construct the complete equilibrium phase diagram for polarizable particles in steady external fields and find that many-bodied, mutual polarization has a remarkably strong influence on the nature of the self-assembled states. Correctly accounting for mutual polarization enables a thermodynamic theory to compute the phase diagram that agrees well with simulations and experiments. Though the equilibrium structures are crystalline, in practice, dispersions typically arrest in kinetically-trapped, disordered or defective metastable states due to strong interparticle forces. This is a key difficulty preventing scalable fabrication of colloidal crystals. I show that cyclically toggling the external field on and off over time leads to growth of colloidal crystals at significantly faster rates and with many fewer defects than for assembly in a steady field. The toggling protocol stabilizes phases that are only metastable in steady fields, including complex, transmutable crystal structures. I use nonequilibrium thermodynamics to predict the out-of-equilibrium states in terms of the toggle parameters. I also investigate the transport properties of dispersions of paramagnetic particles in rotating magnetic fields. Like toggled fields, rotating fields also drive dispersions out of equilibrium, and their dynamics can be tuned with the rotation frequency. I find that the rotating field greatly increases particle self-diffusivity compared to steady fields. The diffusivity attains a maximum value several times larger than the Stokes- Einstein diffusivity at intermediate rotation frequencies. I develop a simple phenomenological model for magnetophoresis through porous media in rotating fields that predicts enhanced mobility over steady fields, consistent with experiments. Lastly, I study the nonlinear dynamics of polarizable colloids in electrolytes and report a new mode of electrokinetic transport. Above a critical external field strength, an instabilty occurs and particles spontaneously rotate about an axis orthogonal to the field, a phenomenon called Quincke rotation. If the particle is also charged, its electrophoretic motion couples to Quincke rotation and propels the particle orthogonally to the driving field, an electrohydrodynamic analogue to the Magnus effect. Typically, motion orthogonal to a field requires anisotropy in particle shape, dielectric properties, or boundaries. Here, the electrohydrodynamic Magnus (EHM) effect occurs for bulk, isotropic spheres, with the Quincke rotation instability providing broken symmetry driving orthogonal motion. In alternating-current (AC) fields, electrophoresis is suppressed, but the Magnus velocity persists over many cycles. The Magnus motion is decoupled from the field and acts as a self-propulsion, so I propose the EHM effect in AC fields as a mechanism for generating a new type of active matter. The EHM "swimmers" behave as active Brownian particles, and their long-time dynamics are diffusive, with a field-dependent effective diffusivity that is orders of magnitude larger than the Stokes-Einstein diffusivity. I also develop a continuum electrokinetic theory to describe the electrohydrodynamic Magnus effect that is in good agreement with my simulations.

Download or read book Brownian Dynamics of Colloidal Suspensions written by Ward Evan TeGrotenhuis and published by . This book was released on 1990 with total page 610 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Orientation Dynamics and Microscope Imaging of Colloidal Suspensions written by Brian David Leahy and published by . This book was released on 2016 with total page 512 pages. Available in PDF, EPUB and Kindle. Book excerpt: Micron-sized colloidal particles provide a unique window into the workings of statistical mechanics. These particles are large enough to be easily imaged with a microscope, allowing for detailed, mechanistic testing of statistical theories, yet small enough to still feel the effects of Brownian motion and thermal forces. Moreover, these thermal forces result in dynamics that are controlled by energy scales at room temperature and time scales on the order of seconds. In addition to allowing detailed control over a colloidal suspension, these accessible scales allow for the possibility of driving the suspension far from equilibrium and the exploration of non-equilibrium statistical mechanics. Much work has focused on the behavior of spherical colloidal particles, which lack an orientational degree of freedom and have simpler dynamics. However, many real suspensions are composed of particles with an orientational degree of freedom. In this thesis I explore the dynamics of dilute suspensions of nonspherical colloidal particles far from equilibrium. First, using an experiment I show that the rotational diffusivity of rodlike colloidal particles is enhanced under shear. Second, using a simplified theory I analytically solve for these dynamics far from equilibrium (in the limit of large Péclet numbers). The e diffusivity is enhanced at a rate proportional to the square of the particle's aspect ratio. Interestingly, this solution also provides insight into the oscillatory shear dynamics of these particles, and into the continuous and oscillatory shear rheology of these suspensions. Third, I use this solution to control the alignment and rheology of a suspension of particles. Finally, I close by improving the microscope's resolution by 10-100x through image analysis alone, without modifying the microscope itself. By improving the resolution we expect to be able to see new dynamics of colloidal particles at unprecedented scales.

Download or read book Non equilibrium Dynamics of Confined Colloidal Suspensions in Shear flow written by Sascha Gerloff and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Non equilibrium Dynamics and Feedback Control of Strongly Confined Colloidal Suspensions in a Planar Shear Flow written by Tarlan Azad Vezirov and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Contact and Macroscopic Aging in Dense Suspensions at the Colloidal Edge written by Francesco Bonacci and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Dense colloidal suspensions (or pastes) constitute a broad class of materials found in areas ranging from environmental systems (e.g. silts, clays), to industry (ceramics, drilling muds, slurries), construction (plaster, cements), foodstuff, cosmetics, pharmaceuticals (toothpaste, medical ceramics). Their most remarkable feature is thixotropy: a slow evolution of their mechanical properties when switching from rest to flow (at fixed density, in the absence of drainage). Thus, their viscosity under flow, or their shear modulus and yield stress at rest, depend both on time and strain history. Thixotropy enables these systems to switch reversibly between solid- and liquid-like states with sharply contrasted properties. At rest, it is usually accompanied with aging--slow, non-exponential dynamics at long times. In recent decades, tremendous progress has been made towards understanding the dynamics of so-called "stabilized" suspensions, in which the formation of interparticle adhesive contacts is fully avoided by tuning inter-particle interactions (via double-layer polarization, or polymer depletion effects). Confocal microscopy was instrumental to such progresses, yet may only be applied to transparent, i.e. nearly index matched, systems, hence is limited to systems in which van der Waals forces are absent. Meanwhile, studies of "non-stabilized" suspensions have tended to focus on very dilute systems (i.e. packing fractions at most a few percent) where a structural evolution (the formation of flocs) could be imaged and thus analyzed, e.g., using light scattering techniques. The tremendous success of these studies has created an observational bias as, today, classical works on suspensions only mention structural dynamics as the root cause of thixotopy. But the pastes of civil and environmental engineering, are dense and generally contain significant concentrations of ions; these screen Coulombic repulsion and allow attractive van der Waals forces to bring particles into solid-solid contacts, which are likely to impact macroscopic properties and their evolution by a number of mechanisms. Indeed, it is well-known that, the macroscopic response of non-colloidal granular materials, is affected by contact friction, which is time- dependent. In cements, the formation of hydrate gels between grains, which determines the late-time strength and mechanical properties of solid concrete, was proposed to play a role in thixotropy. In fact, it remains unclear how solid-solid contacts may affect just the elastic modulus of colloidal systems. By designing an optical trap three-point bending test, Pantina and Furst showed that beams of PMMA and polystyrene particles present a finite flexural modulus, which entails that the contacts formed between particles resist rotation. The flexural modulus of polystyrene particle rods was later shown to evolve in time. These two elements lead us to ask whether the evolution of the contact bending stiffness could be responsible for mechanical aging in pastes, without invoking changes in the network structure. This work aims to investigate the potential existence of a link between contact and macroscopic aging, by combining measurements performed at the particle level, through optical-trap three-point bending tests and confocal microscopy, and at the macroscopic scale, through rheometry. To achieve it, we study the aging behavior of model dense colloidal suspensions composed of silica (SiO2) and PMMA particles suspended in divalent electrolyte aqueous solutions, at moderate concentrations. The use of model ionic systems enables us to carefully control a number of parameters expected to affect the rheology of real suspensions in the dense regime, such as the volume fraction, the size and the shape of the particles and the magnitude of the interactions.

Download or read book Nonequilibrium Dynamics and Self organization in Field Driven Dipolar Colloidal Particles written by and published by . This book was released on 2013 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Colloidal Crystals written by Sharon Jane Gerbode and published by . This book was released on 2010 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloidal crystals, periodic arrays of micron-sized solid particles in solution, offer a unique glimpse of the particle-scale structures and dynamics within a true thermodynamic ensemble. Experimental colloidal studies of melting and crystallization [55, 56, 13, 76, 2] as well as non-equilibrium states such as colloidal glasses [67, 68, 29, 49] have uncovered numerous mechanisms that are experimentally inaccessible in atomic systems due to both small timescales and small lengthscales. The great successes of colloidal physics have emerged as a result of technological advances enabling synthesis of large batches of monodisperse spherical particles. Yet, the crystal structures formed by such particles are limited to variations on layers of close-packed spheres. Consequently, one of the current frontiers in colloidal physics is the study of novel crystal structures formed by non-spherical particles. My thesis work has focused on crystals formed by colloidal dimer particles consisting of two connected spherical lobes. Surprisingly, while the structure of two dimensional crystals formed by the dimers are quite similar to those observed for spheres, the motion of defects within the dimer crystals is significantly different. Geometric obstacles formed by interlocking dimers restrict the motion of defects and ultimately introduce a completely unexpected, previously unreported glassy defect dynamics within a colloidal crystal.

Download or read book Physics Briefs written by and published by . This book was released on 1988 with total page 1008 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Polymer Colloids written by Rodney Priestley and published by Royal Society of Chemistry. This book was released on 2019-12-02 with total page 442 pages. Available in PDF, EPUB and Kindle. Book excerpt: Academic and industrial research around polymer-based colloids is huge, driven both by the development of mature technologies, e.g. latexes for coatings, as well as the advancement of new materials and applications, such as building blocks for 2D/3D structures and medicine. Edited by two world-renowned leaders in polymer science and engineering, this is a fundamental text for the field. Based on a specialised course by the editors, this book provides the reader with an invaluable single source of reference. The first section describes formation, explaining basic properties of emulsions and dispersion polymerization, microfluidic approaches to produce polymer-based colloids and formation via directed self-assembly. The next section details characterisation methodologies from microscopy and small angle scattering, to surface science and simulations. The final chapters close with applications, including Pickering emulsions and molecular engineering for materials development. A comprehensive guide to polymer colloids, with contributions by leaders in their respective areas, this book is a must-have for researchers and practitioners working across polymers, soft matter and chemical and molecular engineering.

Download or read book Flowing Matter written by Federico Toschi and published by Springer Nature. This book was released on 2019-09-25 with total page 309 pages. Available in PDF, EPUB and Kindle. Book excerpt: This open access book, published in the Soft and Biological Matter series, presents an introduction to selected research topics in the broad field of flowing matter, including the dynamics of fluids with a complex internal structure -from nematic fluids to soft glasses- as well as active matter and turbulent phenomena. Flowing matter is a subject at the crossroads between physics, mathematics, chemistry, engineering, biology and earth sciences, and relies on a multidisciplinary approach to describe the emergence of the macroscopic behaviours in a system from the coordinated dynamics of its microscopic constituents. Depending on the microscopic interactions, an assembly of molecules or of mesoscopic particles can flow like a simple Newtonian fluid, deform elastically like a solid or behave in a complex manner. When the internal constituents are active, as for biological entities, one generally observes complex large-scale collective motions. Phenomenology is further complicated by the invariable tendency of fluids to display chaos at the large scales or when stirred strongly enough. This volume presents several research topics that address these phenomena encompassing the traditional micro-, meso-, and macro-scales descriptions, and contributes to our understanding of the fundamentals of flowing matter. This book is the legacy of the COST Action MP1305 “Flowing Matter”.