The ability to manipulate colloidal particles with magnetic fields has profound applications both in industry and academic research ranging from automobile shock absorbers to robotic micro-surgery. Many of these applications use field gradients to generate forces on magnetic objects. Such methods are limited by the complexity of the required fields and by the magnitude of the forces generated. Spatially uniform fields only apply torques, but no forces, on magnetic particles. However, by coupling the particles' orientation and location, even static uniform fields can drive particle motion. We demonstrate this idea using particles adsorbed at curved liquid interfaces. We first review the intersection between active colloidal particles and (passive) particles at the fluid-fluid interface (chapter 1), followed by the introduction of magnetism, magnetic manipulation, and magnetic Janus particle fabrication techniques (chapter 2). In chapter 3, we use magnetic Janus particles with amphiphilic surface chemistry adsorbed at the spherical interface of water drop in decane as a model system to study particle response to a uniform field. Owing to capillary constraints, Janus particles adsorbed at curved interfaces will move in a uniform magnetic field to align their magnetic moment parallel to the applied field. This phenomenon is labeled as the magneto-capillary effect in this thesis. As explained quantitatively by a simple model, the effective magnetic force on the particle induced by static uniform field scales linearly with the curvature of the interface. For particles adsorbed on small droplets such as those found in emulsions, these magneto-capillary forces can far exceed those due to magnetic field gradients in both magnitude and range. The time-varying fields induce more complex particle motions that persist as long as the field is applied (chapter 4). Depending on the angle and frequency of a precessing field, particles orbit the drop poles or zig-zag around the drop equator. Magneto-capillary effects are not limited to Janus particles. Similar behaviors are observed in commercially available carbonyl iron particles. Periodic particle motion at the liquid interface can drive fluid flows inside the droplets, which may be useful for enhancing mass transport in droplet micro-reactors. The magneto-capillary effect at curved liquid interfaces offers new capabilities in magnetic manipulation: even static uniform fields can propel magnetic particles and the use of time-varying fields leads to steady particle motions of increasing complexity. These experimental demonstrations and the quantitative models that accompany them should both inspire and enable continued innovations in the use of magnetic fields to drive active processes in colloid and interface science. The final chapter highlights some specific directions for future work in this area.

Granular materials appear in a broad range of industrial processes, including mineral processing, plastics manufacturing, ceramic component, pharmaceutical tablets and food products. Engineers and scientists are always seeking efficient tools that can characterize, predict, or simulate the effective material properties in a timely manner and with acceptable accuracy, such that the cost for design and develop novel composite granular materials could be reduced. The major scope of this dissertation covers the development, verification and validation of particle system simulations, including solid-liquid two-phase particle mixing process and foaming asphalt process. High shear mixing process is investigated in detail with different types of mixers. Besides particle mixing study, one liquid-gas two phase foaming asphalt simulation is studied to show the broad capacity of our particulate dynamics simulation scheme. Methodologies and numerical studies for different scenarios are presented, and acceleration plans to speed up the simulations are discussed in detail. The dissertation starts with the problem statement, which briefly demonstrates the background of the problem and introduces the numerical models built from the physical world. In this work, liquid-solid two-phase particle mixing process is mainly studied. These mixing processes are conducted in a sealed mixer and different types of particles are mixed with the rotation of the mixer blades, to obtain a homogeneous particle mixture. In addition to the solid-liquid particle mixing problem, foaming asphalt problem, which is a liquid-gas two phase flow problem is also investigated. Foaming asphalt is generated by injecting a small amount of liquid additive (usually water) to asphalt at a high temperature. The volume change during this asphalt foaming process is studied. Given the problem statement, detailed methodologies of particle dynamics simulation are illustrated. For solid-liquid particle mixing, Smoothed Particle Hydrodynamics (SPH) and Discrete Element Method (DEM) are introduced and implemented to simulate the dynamics of solid and liquid particles, respectively. Solid-liquid particle interactions are computed according to Darcy`s Law. Then the proposed SPH coupling DEM model is verified by three classical case studies. For foaming asphalt problems, a SPH numerical model for foaming asphalt simulation is proposed, and simulations with different water contents, pressures and temperatures are conducted and the results agree with the experiments well. The coupled SPH-DEM method is applied to the particle mixing process, and several particle mixing numerical studies are conducted and these simulations are analyzed in multiple aspects. For the solid-liquid particle mixing problem, liquid plays an important role in the mixing performance. The effects of liquid content and liquid viscosity on mixing performance are studied. The mixing indexes of the mixture are applied to analyze the mixing quality, and the differences between three kinds of mixing indexes are discussed. Then mixers commonly used in industry such as Double Planetary Mixer (DPM) are modeled in mixing simulation and their results are compared with the experiments. Similar to other numerical simulation problems, the scale of the model and the accuracy of the simulation results are constrained by the computational capacity. Our in-house software package Particle Dynamics Parallel Simulator(PDPS) has been used as a platform to implement the algorithms above and conduct the simulations. Two parallel computing methods of Message Passing Interface (MPI) parallel computing and Graphics Processing Unit (GPU) acceleration have been used to accelerate the simulations. Speedup results for both MPI parallel computing and GPU methods are illustrated in the case studies. In summary, a comprehensive approach for particle simulation is proposed and applied to particle mixing process and asphalt foaming simulation. The simulation results are analyzed in various aspects to provide valuable insights to the problems studied in this work. Given the improvement of computational capacity, particle dynamics in higher resolution and simulations in more complex configurations can be obtained. This particle simulation platform is general and it can be straightforwardly extended to many-particle systems with more particle phases and solid-liquid-gas dynamics problems.

An experimental study of solid-gas interactions was made for sodium chloride particles, using a specially fabricated environmental chamber in a transmission electron microscope. It was found that under suitable conditions the hydration and dehydration of these particles could be directly observed and quantitatively measured. Measurements of growth were obtained with a time resolution of one-thirtieth of a second for particles having diameters ranging from 0.02 μm to 1.0 μm.

Thesis (Ph.D.)--McMaster University, 2006. / Supervisor: M.F. Lightstone and P. E. Wood Includes bibliographical references (leaves 165-173).

Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains xiii, 97 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 72-74).

Thèse : Astronomie : Paris, Faculté des sciences : 1847. Thèse : Mécanique : Paris, Faculté des sciences : 1847. / Titre provenant de l'écran-titre. Notes bibliogr.

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Thesis (PhD)--University of Stellenbosch, 2004. / Bibliography. Also available via the Internet.

The requirement of a greater understanding of the behavior of solids-gas systems has shown itself profoundly with the advancement of science and technology during recent years. The range and variety of processes in which these systems play an important role is exceptionally broad. These processes range from meteorological disturbances such as dust storms, rain and snow, to the use of vacuum cleaning equipment. With the advancement of aircraft and space technology the influence of these systems is again felt in such cases as the motion of rockets, missiles and aircraft in flight, the behavior of liquid droplets or metallic particles in rocket engines and many other associated problems.