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theses

This thesis is a study of the Hofmeister Series, or specific ion effects, at 3 interfaces: a zwitterionic emulsion interface, a gemini surfactant micelle interface and a neat tetradecane/water interface. The goal of this research is to provide new information such as local pH changes and local counterions concentrations to the specific ion effects research at liquid/liquid interfaces, which might help unveil the origin of specific ion effects. This research utilized a unique chemical probe to study how different ions affect the physical chemical properties of the 3 interfaces. The probe molecule is a long chain amphiphilic arenediazonium ion. In micellar solutions, emulsions and oil/water mixture, the probe associates at the hydrophilic/hydrophobic interfacial region like other amphiphilic molecules do, and then reacts with water molecules and weak nucleophiles to produce corresponding organic products. The yields of products are analyzed by HPLC and used to calculate the interfacial concentrations of ions and water molecules. Using this method we can study the behavior of various ions and molecules at the interfacial region. The background of this method is introduced in Chapter 1. Chapter 2 describes the specific ion effects on the interfacial pH of an emulsion prepared by a zwitterionic surfactant. The headgroup of SB3-14 has different affinities to different anions and cations, which changes ions density at the interfacial region and accordingly alters interface electronic property as well as the interfacial pH. The interfacial pH change was monitored through measuring the reaction rate between a long chain arenediazonium ion and t¬-butylhydroquinone. Chapter 3 is a study of specific counterion effects on gemini surfactants (10-2-10 2X) physical properties such as cmc, aggregation number and interfacial counterion molarity. The ions affect micellar solutions properties in the order of Hofmeister Series. By combining physical characterization means and chemical trapping experiments, the correlation between bulky properties and interfacial properties were observed. Chapter 4 describes the adsorption of different anions onto a neat alkane/water interface. The chemical trapping method was used to probe anions interfacial concentrations at tetradecane/water interface, which were proved to be higher than their bulk concentrations, especially for hydrophobic ions I-, SCN-. Ions adsorption at the interface is supported by other types of experimental and simulation approaches in the literature.

ETD_7645

Ph.D.

Includes bibliographical references

by Xiang Gao

doi:10.7282/T3930WGZ

ETD doctoral

The author owns the copyright to this work.