Document Type

Dissertation

Date of Award

Spring 2018

Degree Name

Doctor of Philosophy in Mechanical Engineering - (Ph.D.)

Department

Mechanical and Industrial Engineering

First Advisor

Pushpendra Singh

Second Advisor

Ian Sanford Fischer

Third Advisor

I. Joga Rao

Fourth Advisor

Denis L. Blackmore

Fifth Advisor

Shawn Alexander Chester

Sixth Advisor

Dibakar Datta

Abstract

The aim of this dissertation is to model the processes by which particles suspended in liquids and at liquid surfaces self-assemble when they are subjected to uniform and non-uniform electric fields. To understand the role of electric forces, three related problems were studied numerically and experimentally.

In the first problem, particles are assumed to be suspended inside a liquid and a nonuniform electric field is applied using electrodes mounted in the domain walls which causes positively polarized particles to collect in the regions where the electric field intensity is locally maximal and the negatively polarized particles collect in the regions where the electric field intensity is locally minimal. A direct numerical simulation (DNS) scheme based on the Maxwell stress tensor (MST) method is developed to simulate the motion.

In the second problem, a uniform electric field is applied to manipulate particles adsorbed on the surface of a drop. The presence of the drop makes the electric field nonuniform and this gives rise to dielectrophoretic forces and an electrohydrodynamic (EHD) flow which cause particles to collect either at the poles or the equator of the drop. The EHD flow, which arises because of the accumulation of charge on the surface of the drop, can be from pole-to-equator or equator-to-pole, depending on the properties of the drop and ambient liquids. When the fluid and particles properties are such that, the EHD and DEP forces are in the opposite directions, particles can be moved from the poles to the equator, or vice versa, by varying the frequency.

In the third problem, a mixture of positively and negatively polarized particles adsorbed on a flat liquid surface was manipulated by applying an electric field in the direction normal to the surface. Both experiments and numerical simulations show that the resulting inter-particle forces cause particles to self-assemble into molecular-like hierarchical arrangements, consisting of particle chains or composite particles arranged in a pattern. The structure of a composite particle depends on factors such as the relative sizes and the number ratio of the particles, and their polarizabilities.

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