(179q) Adsorption Isotherm and Structure of Water of Methyl, Carboxylic Acid, and Hydroxyl Terminated Self-Assembled Monolayers

Recently a lot of research has been done in order to understand water adsorption properties on self-assembled monolayers (SAMs). This is important because water is commonly found on surfaces due to atmospheric humidity. The advances made in understanding interfacial water have contributed to various nanotechnology and biomaterials applications. This study examines the effects of surface chemistry on the adsorption isotherm and structure of water layers on three thiol-based self-assembled monolayers (SAMs) on gold with controlled terminal groups ? methyl, carboxylic acid, and hydroxyl groups. The adsorption isotherms are measured with polarization modulation reflection absorption infrared spectroscopy (PM-RAIRS), ellipsometry, and quartz crystal microbalance (QCM), and the structure of the water layer is deduced from the OH stretching vibration peak positions in PM-RAIRS. The CH3-terminated SAM shows no uptake of water due to the hydrophobic nature of the methyl group. The adsorption isotherm of water on the COOH-terminated SAM shows a strong humidity dependence. The water layer on the COOH surface seems to have a broad distribution of liquid and solid-like structures. The OH-terminated SAM keeps a large amount of water molecules on it even at dry conditions and the adsorption isotherm exhibits little humidity dependence.