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Hofmeister Series at the Liquid/Liquid Interface HOFMEISTER SERIES AT THE LIQUID/LIQUID INTERFACE by XIANG GAO A Dissertation submitted to the Graduate School-New Brunswick Rutgers, The State University of New Jersey in partial fulfillment of the requirements for the degree of Doctor of Philosophy Graduate Program in Chemistry and Chemical Biology written under the direction of Laurence S. Romsted and approved by ________________________ ________________________ ________________________ ________________________ New Brunswick, New Jersey October, 2016 ABSTRACT OF THE DISSERTATION HOFMEISTER SERIES AT THE LIQUID/LIQUID INTERFACE by XIANG GAO Dissertation Director: Laurence S. Romsted 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. ii 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 iii 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. iv DEDICATION To my wonderful parents, Enli Gao and Shaozhen Chen, and to my love, Shangda Guo, for their endless love and support. v ACKNOWLEDGEMENTS First and for most, I would like to thank my advisor Professor Larry S. Romsted for giving me the opportunity to join his group. I thank him for the guidance and mentorship, and the inspiration that he shared with me during my graduate career. It has been my great pleasure to work with and learn from him. I would like to thank all my colleagues in the Romsted research group, especially Dr. Qing Gu, Yongliang Zhang, Dr. Changyao Liu, Dr. Gunaseelan Kanniguna, Dr. Tarek Awad, Dr. Aijaz Ahmad for their generous help and friendship. I really enjoyed working in this friendly environment. I would like to thank Dr. Reiko Oda, Dr. Michel Laguerre, Dr. Dario Bassani at Institut Européen de Chimie et Biologie in Bordeaux, France for their instruction. I would also like to thank other collaborators such as Dr. Jiaji Cheng, Dr. Anne Cheng, Dr. Alla Mallinenko, Dr. Massimiliano Porrini, Dr. Sylvain Nlate. I would like to thank my committee members, Prof. Ralf Warmuth, Prof. John Taylor and Prof. Qingrong Huang for their time, attention, and helpful discussions about my research. I would like to thank Prof Leslie Jimenez for her help during my IFRP and OFRP. And last but not least, I would like to thank my girlfriend Shangda Guo, as well as my parents for their endless support and encouragement through the years of my graduate work and all my life. vi TABLE OF CONTENTS ABSTRACT OF THE DISSERTATION ..................................................................... ii DEDICATION................................................................................................................. v ACKNOWLEDGEMENTS .......................................................................................... vi TABLE OF CONTENTS ............................................................................................. vii LIST OF FIGURES ........................................................................................................ x LIST OF TABLES ....................................................................................................... xvi Chapter 1 General Introduction .............................................................................. 1 1.1 HOFMEISTER SERIES ................................................................................... 1 1.1.1 Introduction................................................................................................... 1 1.1.2 Specific ion effects on surfactant/water interface ......................................... 8 1.1.3 Specific ion effect on neat oil/water interface ............................................. 10 1.2 SURFACTANTS ............................................................................................ 12 1.2.1 Introduction................................................................................................. 12 1.2.2 Micelles ....................................................................................................... 16 1.2.3 Emulsions .................................................................................................... 32 Chapter 2 Specific Ion Effect on Interfacial pH of Zwitterionic Emulsions ..... 35 2.1 INTRODUCTION .......................................................................................... 35 2.2 EXPERIMENTAL SECTION ........................................................................ 39 2.2.1 Materials ..................................................................................................... 39 2.2.2 Preparation of emulsions and determination of kobs ................................... 40 vii 2.2.3 Determining kobs by Azo Dye-Derivatization Method ................................. 41 2.2.4 Typical kinetic data processing .................................................................. 42 2.3 RESULTS ....................................................................................................... 44 2.4 DISCUSSION ................................................................................................. 51 2.5 CONCLUSIONS............................................................................................. 55 Chapter 3 Specific Ion Effect on the Micellization of Gemini Surfactants with Different Counterions ................................................................................................... 56 3.1 INTRODUCTION .......................................................................................... 56 3.2 EXPERIMENTAL SECTION ........................................................................ 59 3.2.1 Synthesis of gemini surfactants ................................................................... 59 3.2.2 Chemical Trapping Experiments ................................................................ 63 3.2.3 Electrical conductivity measurements ........................................................ 67 3.2.4 Ionization degree, α .................................................................................... 68 3.2.5 Free energy of micellization ....................................................................... 69 3.2.6 Aggregation Numbers ................................................................................. 70 3.3 RESULTS ....................................................................................................... 71 3.3.1 Physical chemical properties of carboxylate gemini surfactants ............... 71 3.3.2 Interfacial counterion molarity ................................................................... 76 3.4 DISCUSSION ................................................................................................. 80 3.5 CONCLUSION ............................................................................................... 90 3.6 SUPPLEMENTARY INFORMATION ......................................................... 91 Chapter 4 Specific anions adsorption at neat water/oil interface ....................... 99 4.1 INTRODUCTION ........................................................................................ 100 viii 4.2 EXPERIMENTAL SECTION ...................................................................... 102 4.2.1 Materials ..................................................................................................
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