Physical Chemistry of Limonene Microemulsions
and their Interaction with Oil

Abstract

This thesis aims to study the phase behaviour of limonene microemulsions using a formulation used in industry for enhanced oil recovery. The use of a stopped-flow FRET technique was able to elucidate a mechanistic study of micelle fusion kinetics with respect to limonene microemulsions.

The first part of the project used several phase measurement methods and spectroscopic techniques to determine the physical properties of a limonene microemulsion using a commercial surfactant and the phase behaviour of its components. The various techniques employed are useful tools for future formulators when studying limonene microemulsions. The commercial surfactant, despite showing branching was deemed suitable as an alternative to pure C12E7, exhibiting behaviour expected of pure C12E7. The phase measurements also gave insight to the kinetic mechanistic studies that followed.

The second part of the project investigated a suitable method to observe micelle exchange kinetics for limonene microemulsions and derive quantifiable kinetic data. A stopped-flow FRET technique was used to observe the exchange and Target Factor Analysis was used for quantitative analysis. Initial trials using pyrene as a fluorescent dye was not suitable due to insufficient solubility of the fluorescent probe within the micelles. The use of FRET probes was successful in observing micellar exchange on a timescale that was detectable (>8 ms). Target Factor Analysis gave significantly improved clarity to the data obtained and allowed me to deduce micelle fusion kinetics from the observed data. The stopped-flow FRET technique combined with Target Factor Analysis is a novel approach to the study of micelle fusion kinetics.

The final part of the project used the stopped-flow FRET technique to compare micelle exchange kinetics with similar microemulsion systems, determine the effect of temperature, concentration, and introduction of salt on micelle exchange. This was taken further, observing the interaction of limonene microemulsions with a crude oil mimic. By comparing several microemulsion systems and changes in environment, a greater understanding of the kinetic pathways micelles can take in fusion processes was garnered. The use of the stopped-flow FRET technique using a crude oil mimic demonstrates the capability of the technique for future use on oil surfaces.