Approaches to the quantification and investigation of interfacial systems and their materials properties using sum frequency generation spectroscopy

The focus of this thesis is the use and methods development of sum frequency generation (SFG) spectroscopy as an analytical tool for studying surfaces of CO2-philic molecules. The specific set of molecules used for analysis in this project was peracetylated carbohydrates due to their inherent solubility in liquid and supercritical CO2. The goal of the project was to investigate the specific interactions present at the surface of these materials in contact with CO2 under varying conditions. To accomplish this task however, it was necessary to study the materials properties of these compounds using a variety of techniques and relate the SFG data collected under ambient conditions to changes in the long range order. During the analysis of the materials properties the sensitivity of diffuse reflectance sum frequency generation (DR-SFG) spectroscopy to changes in crystallinity was elucidated. In addition, a method was developed and validated for quantitative analysis of changes in concentration of bulk mixtures. Specifically, mixtures of materials differing only in crystal structure were studied and linear calibration plots were created allowing the determination of an unknown samples mole fraction. The last set of control experiments included study of the CO2 adsorption of peracetylated carbohydrates using a high pressure quartz crystal microbalance (QCM) to understand how these surface interactions occur below each material's deliquescence point. By understanding the molecular interactions of this class of CO2-philes in terms of the adsorption thermodynamics and the importance of long range order, deconvolution of subsequent SFG experiments involving changes in CO2 pressure can be accomplished. Finally, the first pressurized SFG experiment was performed on thin films to see how changes in the viscosity and density of CO2 effect the specific interactions at the surface. By relating information collected previously with SFG data collected under varying CO2 environments, a more in depth picture of the interactions at the surface of these materials was developed.