| The aim of this dissertation is to contribute to better understanding of the chemistry at liquid interfaces by the means of nonlinear optical techniques, mainly Second Harmonic Generation (SHG). It contains five chapters.;Chapter 1 is a brief survey of interface studies and the introduction of the aims and scope of this dissertation.;Chapter 2 is a summary of the advances, principles and methods of SHG applicable to interface studies.;Chapter 3 studies acid-base equilibrium at liquid interfaces. First presented is the measurement of the acid-base equilibrium constant, i.e. pKa, of the insoluble monolayer of a long chain C;Chapter 4 systematically studies the polarity of immiscible fluid interfaces. The polarity of the air/water interface is obtained with polarity indicator molecules, N,N-diethyl-p-nitroaniline (DEPNA) and ET(30) by SH spectra measurements. The polarities of 1,2-dichloroethane/water and chlorobenzene/water interfaces are also determined with DEPNA. These results indicate that the interfacial polarity equals the arithmetic average of the polarities of the two bulk fluid phases. The generality of this surprisingly simple relationship is discussed. The results on interfacial polarity are very important in understanding solute/solvent interactions and predicting interfacial properties from bulk measurements.;Chapter 5 for the first time measured the enhancement effect of SHG from spherical particle interfaces in bulk solution. By this new method, the adsorption isotherm of Malachite Green (MG) dye molecules is obtained for polystyrene particles and an oil/water emulsion interfaces. These data are analyzed successfully with a Modified Langmuir Model proposed here. The establishment of the principle and methods in studying complex interfacial systems, which have not been efficiently studied and are little understood so far, with non-linear optical methods, is a major breakthrough in colloid and interface science. |
