Date of Award

4-2011

Embargo Period

10-17-2012

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Advisor(s)

Lynn M. Walker

Second Advisor

Shelly J. Anna

Abstract

Surfactants are important in countless fields of research and industrial processing. Their value is inherently dependent on our ability to characterize their fundamental transport parameters, such as diffusion coefficients and kinetic rate constants, and thus predict their dynamic and equilibrium behavior in a wide range of applications. However, current techniques of measuring and analyzing surfactant transport to fluid-fluid interfaces are confounded by the inability to decouple kinetics and diffusion. This thesis outlines a new methodology of analyzing surfactant dynamics using a time scale analysis that definitively identifies the relevant transport mechanisms. A new device is designed and implemented, which measures surface tension at microscale interfaces in order to validate the scaling analysis. The device has several advantages over conventional techniques: namely measures surface tension in-situ, performs faster, and requires significantly less volume. Concentration, radius of the interface, and convection are shown to be important parameters in observing a transition from diffusion-limited to kinetic-limited dynamics. Measuring kinetic-limited dynamics is necessary to accurately measure kinetic rate coefficients of surfactants. The scaling analysis is demonstrated on a family of nonionic surfactants, CiE8 at the air-water and oil-water interface. The analysis and instrumentation introduced in this thesis will be instrumental in characterizing new and innovative surfactant molecules; as well as furthering our understanding of the relationship between molecular structure and fundamental transport parameters.

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