Book Description

The behavior of molecules in condensed phases involves complex considerations to fully describe the microscopic structure and dynamics. This is particularly interesting in complex liquids with inherent heterogeneity and in binary mixtures where the competition between the interactions between similar and dissimilar species greatly affects the microstructures of the liquid. The ubiquity of aqueous binary mixtures necessitates their study, particularly because the unique properties of water often manifests anomalously in the physical properties of binary mixtures. These changes in physical properties are the result of structural changes at the molecular level. In this thesis, the dynamical results from optical heterodyne-detected optical Kerr effect (OHD-OKE) experiments are reported for a series of aqueous binary mixtures. OHD-OKE is a nonresonant pump probe technique in which the bulk orientational dynamics of a liquid are measured via the time-dependent birefringence induced in the sample by an optical pulse. The OHD-OKE setup used in this thesis has the ability to measure dynamics over seven decades of time and eight decades of signal, which is an incredible window for a single experimental technique. Ultrafast pulses, which are necessary to have sufficient resolution, are generated by a Ti:Sapphire oscillator/regenerative amplifier. Multiple techniques including heterodyne detection and phase cycling are used to improve signal to noise, particularly at long time when signals are small. The theory behind OHD-OKE and a description of the experimental setup are given here. In addition to dynamical information, microstructural changes can be extracted from OHD-OKE data using the Debye Stokes Einstein (DSE) equation. The specific structures can be elucidated using complementary techniques. The remainder of the thesis is devoted to the aqueous binary mixtures of interest and the results from OHD-OKE and complementary techniques. First, a protic ionic liquid is compared to its aprotic analogue in order to better understand the role of hydrogen bonding in ionic liquids at various hydration levels. This work is further expanded to ionic liquids of varying chain lengths and anions in order to provide a deeper understanding of hydrophilicity and water saturation in ionic liquids. Finally, the anomalous phase behavior of the nicotine/water binary system is studied in order to elucidate the dynamics and microstructures associated with the lower critical solution temperature.