Date of Award

Spring 2012

Document Type

Dissertation

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

Anthony D. Rosato

Fifth Advisor

Denis L. Blackmore

Abstract

Particles floating on fluid-liquid interfaces are of considerable interest because of their importance in a range of physical applications and biological processes, e.g., self-- assembly of particles at fluid-fluid interfaces resulting in novel nano structured materials, stabilization of emulsions, formation of pollen and insect egg rafts, etc. The aim of this dissertation is to explore the mechanism by which particles are adsorbed at fluid-liquid interfaces. It is shown that the inertia of a particle plays an important role in its motion in the direction normal to a fluid-liquid interface, and in determining the particles adsorption trajectory and orientation in the adsorbed state. Although the importance of inertia diminishes with decreasing particle size, on an air-water interface the inertia continues to be important even when the particle size is as small as a few nanometers.

This dissertation also investigates the vertical oscillations of a particle while it is being adsorbed on an interface. The fact that the particle oscillates vertically implies that its behavior is similar to that of an under-damped mass-spring-dashpot system, and that it has characteristic linear and rotational frequencies which depend on the physical properties of the fluids involved and those of the particle. The experimentally measured frequency of oscillation of a particle is in approximate agreement with the frequency calculated analytically, which is noteworthy considering that the latter depends only on the fluid and particle properties, and that there are no adjustable parameters in the analytic expression. It is shown that similarly to an under-damped system, these characteristic frequencies can be excited by an external forcing.

When a particle is adsorbed on a fluid-liquid interface it induces a relatively strong transient flow in the liquid which persists for several seconds. For a spherical particle the flow is axisymmetric about the vertical passing through the particle’s center. To visualize this flow, an experiment is designed based of the Particle Image Velocimetry (PIV) technique. The measurements show that the fluid directly below the particle rises up, and near the interface it moves away from the particle. The velocity near the interface is found to be about an order of magnitude larger than in the liquid below the particle.

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