FOURIER-TRANSFORM IR STUDY ON STRUCTURAL EVALUATION OF EVAPORATED ORGANIC THIN-FILMS .1. CHANGES IN MOLECULAR-ORIENTATION OF NORMAL-PARAFFINS BY HEAT-TREATMENT

In situ Fourier transform IR (FT-IR) measurements were conducted on evaporated thin films and bulk samples of n-C33H68 in order to evaluate the changes in molecular orientation during heating to the molten state. The thermal transitions observed by the FT-IR method were in good agreement with analogous data obtained by calorimetric techniques. The spectroscopic data exhibited clearly that there occur substantial changes in the degree of absorbance as well as the frequencies in several vibrational modes, especially the CH2 stretching mode, owing to changes in the molecular orientation and to phase transitions from phases A, B, C and D to the molten state. Moreover, these changes in FT-IR spectra differed greatly depending on the sample conditions (i.e. bulk or evaporated thin film samples) and the type of substrate on which the samples were evaporated.