Temperature-Induced Molecular Reorganization in Thin Films and on Surfaces as Observed by Grazing Incidence Infrared Spectroscopy

With the use of a thermostated grazing incidence reflection (GIR) infrared cell, spectra of organic monolayers and thin polymer films have been obtained as a function of temperature. Results indicate that insight into the mechanism of molecular reorganization which often occurs at elevated temperatures can be obtained through thermal cycling experiments. In particular, studies of ultrathin poly(methylmethacrylate) [PMMA] films as a function of temperature reveal the onset of molecular segmental motion known to occur at the glass transition temperature, T_g (∼100°C). Similarly, in Langmuir-Blodgett (L-B) monolayers of cadmium arachidate (CdA), GIR measurements indicate that a two-stage disordering process occurs with increasing temperature. Pretransitional disordering of the hydrocarbon tails may be a contributing factor to the onset of the thermal melting point.