Structure-dependent viscoelastic properties of C-9-alkanethiol monolayers

Quartz crystal microbalance techniques and in situ spectroscopic ellipsomet ry are used to probe the structure-dependent intrinsic viscoelastic propert ies of self-assembled CH3(CH2)(8)SH alkanethiol monolayers adsorbed from th e gas phase onto Au(111)-textured substrates. Physisorbed molecules, mixed chemisorbed-fluid/solid phases and solid-phase domain boundaries make seque ntially dominant contributions to the measured energy dissipation in the gr owing monolayer. Deviations from Langmuir adsorption kinetics reveal a prec ursor-mediated adsorption channel. These studies reveal the impact of struc tural heterogeneity in tribological studies of monolayer lubricants.