Investigation of Molecular Structures and Ordering at Solid Liquid Interfaces Using Novel Emersion Vibrational Spectroscopy

Abstract

Molecular level understanding of solid-liquid interfaces in ambient condition is still a challenging, but exciting area. The work presented here demonstrates the effectiveness of emersion IRRAS as a new tool in our arsenal to expand our understanding of solid-liquid interfaces through the investigation of model solvent/organically modified interfaces and electrochemically relevant interfaces using novel emersion spectroscopy. The emersion approach effectively isolates the molecularly-thin emersed liquid layer under ambient conditions by physically removing bulk liquid from the interface. Without the interferences from bulk liquid, the emersed layer is accessible with conventional spectroscopic methods.In this work, development and implementation of emersion IRRAS is first described. Emersion IRRAS was used to investigate the model solvents water and methanol at three w-terminated-SAM-modified Ag surfaces (11-MUA, 11-MUD, and UDT-modified Ag) possessing a range of surface energies. These surfaces had been previously characterized with emersion Raman spectroscopy and/or ellipsometry. Furthermore, solvation of CO on Pt by three solvents (methanol, acetonitrile, and water) was investigated in an effort to attain molecular-level insight into electrochemically-relevant interfaces.Experimental results presented show successful implementation of emersion IRRAS. For each of the systems studied, interfacial solvent spectra clearly differed from those of bulk solvents indicating unique molecular structures of emersed liquids.