Thermal Behavior of Langmuir-Blodgett Films. 1. Electron Diffraction Studies on Monolayers of Cadmium Stearate, Arachidate, and Behenate

Article abstract of DOI:10.1021/j100354a039

Electron diffraction patterns of monolayers of several cadmium fatty acid salts were studied as a function of the sample temperature.A sharp decrease of the diffraction peak intensities at temperatures well below the main melting temperature of the headgroup lattice indicates a pretransitional disordering.It depends on the chain length and starts at ca. 35 deg C for cadmium stearate, at ca. 55 deg C for cadmium arachidate, and at ca. 75 deg C for cadmium behenate.The hexagonal geometry of the diffraction patterns does not change with temperature, and the radial and angular full width at half-maximum increase only slightly compared to the pronounced decrease of the intensity.This indicates that the overall bond orientational and traslational order of the molecules is preserved and that the intesity decrease is caused by thermally induced random tilt orientational disorder or bending of the chains.