Graduate Thesis Or Dissertation


A study of the dynamics and rheology of passive and active suspensions of particles with various geometries Public Deposited

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  • Suspensions of particles in fluids are everywhere in our life, such as paints, pharmacies, food, etc. Suspensions can exhibit properties that common fluids do not possess. For example, the paint needs to flow well when brushing so that it can be smeared on the wall, which is aided by the shear-thinning of the fluid. However, when brushing stops, paint needs to stay still on the wall, which is aided by the yield-stress of the paint. These types of behavior depend on the dynamics and microstructures of the suspensions. Suspensions of particles can serve as precursors of composite materials, for example, a composite can be created by curing a suspension of particles in a monomer solution. In such case, the properties of the composite can be affected by the dynamics of the fluid. Investigating the dynamics of suspensions of particles can be crucial to the manufacture of composite materials. This study covers theoretical, computational, and experimental studies of suspensions of particles in various aspects, such as suspensions of spherical and aspherical particles, suspensions with or without external fields, and suspensions in Newtonian and non-Newtonian fluids. The theoretical and computational study focuses on a fundamental investigation of the dynamics of the suspending particles. Under a magnetic field, magnetic disks can be aligned by a magnetic field. An analytic solution that describes the motion of a single magnetic disk under a rotating field is derived in this study, and it has shown good comparison with experimental data. When multiple particles are present in the fluid, the particles interact with each other hydrodynamically and magnetically if a magnetic field is applied. Under the influence of the magnetic field, the microstructures of the material can be altered. The dynamic behavior depends on hydrodynamic interactions. I discuss the hydrodynamic and magnetic interactions from a fundamental point of view, and I implement a computational method called Stokesian dynamics to simulate such systems. Furthermore, I also discuss a way of simulating aspherical suspensions that is based on the spherical suspensions. The experimental study focuses on the characterization of complex fluids by suspending microparticles as the probes that can measure the local properties of fluids, and the method is called microrheology. The complex fluids that are characterized in this study serve as an inexpensive substitute of the sputum of cystic fibrosis (CF) patients. The goal of this part of the study is to explore an efficient drug-delivery vehicle that can transport through the mucus of CF patients. The formula of the substituting fluids that are proposed by our lab has shown similar rheological properties with the sputum from CF patients in the macroscopic lengthscale. I also characterized the fluids in the microscopic lengthscale and I have seen differences between the macroscopic and microscopic properties. I deduce that the differences arise from the heterogeneity of the fluids, which cannot be well detected in the macroscopic method. Finally, I combine the knowledge that we obtain from the theoretical study with the technique that we utilize in the experimental study to obtain a proof-of-concept study. We have successfully suspended microdisks in a yield-stress fluid so that the microdisks can be aligned while constrained in the elastic cages of the fluid. The yield-stress is characterized by a microrheological technique, and we apply the scalings that we have derived previously to control the parameters to achieve the goal of aligning microdisks while suppressing the translations of microdisks.
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  • NSF Career Award
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