The characterization of structural disorder in thin films at elevated temperatures by spectroscopic methods

Abstract

Changes in the IR bandshapes and shifts in frequency can provide an insight into the nature of molecular motion occurring prior to structural reorganization which accompanies a phase transition. In the case of Langmuir-Blodgett films of polymerizable molecules, often there is competition between polymerization and the occurence of structural disorder when monomeric films are subjected to elevated temperatures. To distinguish these two mechanisms, a series of melting experiments on L-B films of cadmium arachidate were under-taken using grazing incidence reflection techniques to assess the change in molecular orientation and order as a function of temperature: The spectroscopic observations being correlated with DSC measurements. Similar thermal and spectroscopic studies of octadecyl-fumarate [H(CH2)180C(0)CHCHC00]2, Cd indicated that although the resulting polymer was structurally similar to that obtained by UV irradiation at ambient temperature, the orientation of the hydrocarbon side chain and the backbone bridging group (-0C(0)CHCH-) was disrupted owing to the thermal disorder introduced prior to or at the time of polymerization. © 1985 SPIE.