Date of Award

8-2004

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemical Engineering

Major Professor

Robert M. Counce

Committee Members

David J. Keffer, David W. DaPaoli, Raymond A. Buchanan

Abstract

This dissertation presents a model capable of predicting equilibrium oil droplet contact angles on a solid surface immersed in surfactant solution, a thorough discussion of the effects of surfactant concentration and salt addition on contact angles, and an experimental investigation into the impact of voltage application to the solid surface on oil droplet shape in an aqueous/organic/solid system. The work contained in this dissertation resulted in five journal articles and numerous presentations.

The model applies current theories of surfactant self-assembly, the quasi-chemical approximation for solid surface adsorption, and various aqueous/organic/solid system properties to determine organic droplet contact angles. The computational methodology employed by the model requires the description of the aqueous/organic/solid system by selected component balances and through numerical techniques determines the equilibrium component distribution and the organic droplet contact angle for the specific system. Results from the model are compared to experimental contact angle data for various surfactants, surfactant concentrations, salt concentrations, and surface materials.

The investigation into the effects of low magnitude applied voltage on droplet phenomena and oil removal determined that significant changes in droplet shape and removal efficiency can occur for voltages between ±3.0 volts. These changes in droplet shape where then compared to observed improvements in ultrasonic oil removal from metal surfaces in aqueous solutions. Employing the theoretical understanding of aqueous/organic/solid systems a discussion of controlling phenomena and mechanisms was presented.

I have shown that (1) organic droplet contact angles on solid surfaces in aqueous/organic/solid systems are significantly affected by aqueous/ solid interfacial surfactant aggregation, (2) this impact is due to changes in the structure of the surfactant aggregate itself, (3) these changes are heavily impacted by surfactant concentration and the addition of low concentration salt to the aqueous surfactant solution, (4) the type of salt added to the solution is of greater relevance than indicated in the existing literature, and (5) that the application of low voltage applied potentials can significantly effect droplet shape and oil removal efficiency in an aqueous/oil/solid system.

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