?Pub Inc A computational study of pair-wise interactions between drops and the dynamics of concentrated emulsion is undertaken using a three-dimensional front-tracking finite difference method. The study is motivated by numerous industrial and domestic applications of multi-fluid flow. We first investigate the effects of inertia on pair-wise interaction between drops in a Newtonian system. It is seen that at high Re, increase in the initial cross-stream separation between the two interacting drops slightly increases the drops deformation. In addition, it is observed that if the separation position of the two interacting drops along the flow direction is so small that the drops can slide past each other even at high Re, increase in Re leads to an increase in the drops' lateral displacement after separation. However, if the separation position of the two interacting drops is more than twice the undeformed radius of the drops, the drops may not be able to slide past each other if Re is sufficiently large. The deformability of the drops also affects their lateral displacement. We observe that deformable drops are not able to slide past each other under the same conditions where drops with very low Ca can slide past each other. It appears that the flow modification caused by the drops deformation creates a downward force on the left drop. Next, we examine the effects of inertia on drop dynamics in a concentrated emulsion. We observe that the effects of inertia on weak hydrodynamic interaction at low dispersed phase volume fraction do not result in increased volume-averaged drop deformation. However, for concentrated emulsions, interaction between drops at increased Re leads to an increase in volume-averaged drop deformation especially when Ca of the drops is low. A single drop tends to rotate towards the vertical direction at increased Re. However, interactions between drops suppress this tendency. Finally, we investigate the effects of viscoelasticity on interactions between drops. We notice that the interaction between viscoelastic drops is similar to that between Newtonian drops. However, we observe that the interaction in the case of Newtonian drops in a viscoelastic matrix is different from that of Newtonian fluids. Viscoelastic stresses in the matrix-phase viscoelastic system inhibit the drops' lateral displacement and cause the drops to align more with the flow direction. Similar to what has been observed in single-drop deformation, the De of the matrix-phase viscoelasticity has non-monotonic effects on the drops' deformation when the drops are aligned with each other along the compressional quadrant of the shear flow.

We next investigate the material response of an emulsion of such drops. A numerical methodology for calculating the rheological stresses based on drop shapes is developed. We use it to study the rheology of a dilute emulsion in steady shear as well as oscillating extensional flow at finite inertia. Inertia-induced morphological change of drops gives rise to abnormal rheological responses such as shear thickening and sign change of normal stresses in shear flow, and a negative elastic modulus in oscillating extensional flow.

In recent years, droplet microfluidics has been increasingly popular in chemistry and biology where biological or chemical samples are encapsulated in nL-pL droplets. Some typical applications are using droplet microfluidics as a flow cytometer, as a drug discovery platform, for nanoparticle synthesis, and for tissue engineering. Unlike solid wells in multi-well plates, droplets are prone to instabilities at the liquid--liquid interface. They can undergo coalescence or break-up, and compromise the accuracy of the assay. While coalescence has been avoided by using appropriate stabilizers, the break-up of droplets--especially those within a concentrated emulsion--remains a limiting factor affecting the throughput of the assay, in particular during droplet content interrogation step. Unfortunately, previous studies on single droplet break-up cannot provide a thorough explanation as to why droplets break in highly concentrated emulsion flow in confined space. Furthermore, most present literature studies emulsion interactions and rheology in the macro-scale and don't study droplet-droplet interactions and individual droplet break-up within a highly concentrated emulsion flowing in a confined space. Thus, this work aims to study the physics of droplet break-up in a highly concentrated emulsion flowing into a narrow constriction. This work is categorized into three parts: (1) Quantify the droplet break-up probability at various flow parameters, channel geometries, and emulsion properties (2) Study the effects of drop pair interactions in a highly concentrated emulsion flow that leads to droplet break-up (3) Study the effects of drop shapes in a highly concentrated emulsion flow that leads to droplet break-up For the first part, the statistics of droplet break-up within a highly concentrated emulsion entering a narrow constriction at various flow parameters, channel geometries, and emulsion properties. It was found that there exist a scaling law for the break-up probability at various capillary number. For the second part, the drop pair interactions as they enter the narrow constriction are studied. It was found that the relative drop pair locations as the drops are entering the narrow constriction is a dominant factor in determining the drop break-up outcome. Three regimes were found where drops will either have a break, not break, and bistable outcome. For the third part, the drop shape as they enter the narrow constriction are studied. It was found that there are a diverse range of drop shapes occurring as the drops are entering the narrow constriction. This leads to drastically different stress balances for each individual drops as they enter the narrow constriction. For this part, a machine learning model and training strategy is proposed to describe droplet shapes and predict its break-up outcome accurately. In conclusion, this work represents a critical step towards the understanding of the physics governing drop instability in a highly concentrated emulsions flowing into a narrow constriction.

In particulate flows, the flow inertia impacts the motion and size distribution of the particles and this in turn, has a strong implication on global behavior of the emulsions such as their rheological properties. As such, the central goal of most of the investigations on dispersed multiphase flow, so far, has been to understand the phase distribution of particles and to correlate the global behavior of the system with these parameters. For pressure-driven flows in a channel, it is known that the velocity gradient in the channel leads to a lateral force whose magnitude and direction depends on the viscosity and density ratios of the fluids and the drop deformation. This lateral (lift) force is the primary reason behind the various observed modes of phase distribution of the particles. Unfortunately, most of the studies conducted so far have been concerned with the solid particles and for flows at low to moderate Reynolds numbers. Little is known about the dynamics of deformable drops at high Reynolds numbers. The goal of this study is to bridge the gap by direct numerical simulations. A front tracking/finite difference technique is used to solve the Navier-Stokes equations in the fluids inside and outside of the drops. Initially, the drops are randomly distributed in the computational domain their evolutions are followed for a sufficiently long time so that the system reaches a quasi-steady state. The statistics about the flow were then extracted. As the Reynolds number increased the equilibrium height found shifted towards the channel wall in both single and multidrop simulations. Similar effects were found by increasing the Weber number, and decreasing the viscosity ratio, density ratio, and area fraction.

This volume offers a unified treatment and critical review of the literature related to the fluid dynamics, heat transfer, and mass transfer of single bubbles, drops, and particles. 1978 edition.

Bubbles, Drops, and Particles in Non-Newtonian Fluids, Second Edition continues to provide thorough coverage of the scientific foundations and the latest advances in particle motion in non-Newtonian media. The book demonstrates how dynamic behavior of single particles can yield useful information for modeling transport processes in complex multipha

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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.

Covering colloids, polymers, surfactant phases, emulsions, and granular media, Soft and Fragile Matter: Nonequilibrium Dynamics, Metastability and Flow (PBK) provides self-contained and pedagogical coverage of the rapidly advancing field of systems driven out of equilibrium, with a strong emphasis on unifying conceptual principles rather than material-specific details. Written by internationally recognized experts, the book contains introductions at the level of a graduate course in soft condensed matter and statistical physics to the following areas: experimental techniques, polymers, rheology, colloids, computer simulation, surfactants, phase separation kinetics, driven systems, structural glasses, slow dynamics, and granular materials. These topics lead to a range of exciting applications at the forefront of current research, including microplasticity of emulsions, sequence design of copolymers, branched polymer dynamics, nucleation kinetics in colloids, multiscale modeling, flow-induced surfactant textures, fluid demixing under shear, two-time correlation functions, chaotic sedimentation dynamics, and sound propagation in powders. Balancing theory, simulation, and experiment, this broadly-based, pedagogical account of a rapidly developing field is an excellent compendium for graduate students and researchers in condensed matter physics, materials science, and physical chemistry.

Intermolecular and Surface Forces describes the role of various intermolecular and interparticle forces in determining the properties of simple systems such as gases, liquids and solids, with a special focus on more complex colloidal, polymeric and biological systems. The book provides a thorough foundation in theories and concepts of intermolecular forces, allowing researchers and students to recognize which forces are important in any particular system, as well as how to control these forces. This third edition is expanded into three sections and contains five new chapters over the previous edition. - Starts from the basics and builds up to more complex systems - Covers all aspects of intermolecular and interparticle forces both at the fundamental and applied levels - Multidisciplinary approach: bringing together and unifying phenomena from different fields - This new edition has an expanded Part III and new chapters on non-equilibrium (dynamic) interactions, and tribology (friction forces)