A novel strategy to investigate interfaces relevant to chromatographic separations is presented. The strategy in this dissertation relies on three key ideas: 1) design and fabrication of appropriate model of chromatographic interface, 2) use of forced dewetting to separate interfacial constituent of mobile phase from its bulk component yet preserves the interface, and 3) use of IR spectroscopy and ellipsometry to investigate the structure and thickness of isolated interface.Stratified structures of ultrathin (< 10 nm thick) silica films on gold using gold oxide as adhesive layer and wetting control agent are used as model solid phase. Such design provides chemical environment of bulk silica surface, does not introduce significant spectral background, is suitable for reflection-based spectroscopies, and allow for easy modification to mimic wide range of silica - solvent interfaces. Bare silica-water models capillary electrophoresis interfaces; water-methanol mixture at octadecylsilane-modified silica represents reversed phase liquid chromatography interfaces.Forced dewetting is used to decouple interfacial constituent of mobile phase from its bulk component; yet, the integrity of interface is preserved. This approach, combined with the use of IR spectroscopy and ellipsometry, allowed for ambient atmosphere characterization of these interfacial layers in terms of their structure, composition, and thickness for water at bare silica. Hydrogen bonding was probed in case of complex water-methanol binary mixture at octadecylsilane-modified silica surface.The analysis of residual water layers formed by forced dewetting at bare silica as a function of bulk solution pH shows that the structure of the interfacial layer is highly ordered compared to bulk, and is also pH dependent. Further, thicknesses of interfacial layers were found to be pH dependent and vary from ~6 (pH 1) to ~9 nm (pH 9). Gouy-Chapman-Stern double layer was found to be inadequate to satisfactorily describe observed trends. In addition, surface enhanced infrared absorbance phenomenon was also observed that aided increased quality of resulting IR spectra.The analysis of residual water-methanol layers formed by forced dewetting at octadecylsilane-modified silica surface as a function of gas phase atmosphere shows that the structure of the interfacial layer is highly dependent on the composition of gas phase. The observed changes indicate that condensation of methanol from gas phase into residual layer and/or evaporation of water from residual layer into gas phase may occur in used experimental setup used in this dissertation. For that reason, more precise quantification of relative amounts of water and methanol in residual layers was precluded. Yet, regardless of investigational conditions, two different hydrogen bonding environments for methanol were distinctively observed.

The process of forcibly dewetting a solid substrate from a bulk liquid so as to leave a thin residual layer on the surface is referred to as forced dewetting. This novel experimental approach helps to investigate interfacial species by minimizing the interference of the bulk liquid when coupled with spectroscopy. In this work, the scope of liquids investigating using this approach has been expanded from simple fluids to one type of complex fluid, a nematic liquid crystal, 4-n-pentyl-4'-cyanobiphenyl (5CB).In order to better understand the interfacial behavior of the simple fluids, water, chloroform, and n-pentane vapors were adsorbed onto omega-terminated SAM-modifed Ag (11-mercaptoundecanoic acid, 11-mercaptoundenanol, and undecanethiol) surfaces under vapor-saturated conditions. The kinetics of solvent adsorption on each of these surfaces were investigated and the thicknesses of the adsorbed layer were compared to predictions from Lifshitz theory of long-range van der Waals interactions. Although the predicted thicknesses do not match the experimental values for adsorbed films, the predicted thicknesses do match those observed experimentally using forced dewetting. The correlation between these predicted and observed thicknesses implies that residual film formation under the conditions of forced dewetting used in this laboratory is dictated by interfacial forces alone.The surface adsorption behavior of 5CB was investigated using surface-enhanced Raman spectroscopy with the aid of localized surface plasmon resonances-surface plasmon polaritron coupling. The results clearly indicate that 5CB is adsorbed to smooth Ag surface in a facial orientation with pi-d orbital interaction suggested.Finally, forced dewetting studies of bare, -NH2-temintaed SAM, and -CH3-temintaed SAM modified-SiO2 substrates from 5CB were undertaken. Residual layer thicknesses were monitored as a function of substrate velocity. The transition from the regime in which interfacial forces dictate residual layer thickness to the regime in which fluid dynamic forces dictate thickness was observed for the first time and was evaluated in terms of the average 5CB director orientation. Unlike simple fluids, 5CB has strong interfacial interactions from surface anchoring depending on the chemical nature of the substrate, which makes the residual layer thicknesses at least 100 times larger than observed in simple fluids.