title: Thermally induced conformational changes of Ca-arachidate Langmuir-Blodgett Films at different compression.
abstract: The conformational order in Ca-arachidate Langmuir-Blodgett films on solid glass supports is investigated by means of vibrational sum-frequency generation spectroscopy (VSFG). The symmetric C-H stretching vibrations of both the terminal methyl and the methylene groups are utilized to monitor the chain conformation at various sample temperatures under ambient conditions. At room temperature the film is well-ordered consisting almost entirely of all-trans configured chains. Between 340 and 430 K we observe a marked increase in gauche-defects before oxidative degeneration starts at sample temperatures above 470 K. The temperature dependence of the data is well represented by apparent enthalpy changes for the formation of gauche-defects, sharply increasing with packing density from 29 to 62 kJ/mol; values, which are an order of magnitude larger than those of the gas phase molecule. These large apparent enthalpies do not prevent the formation of a high degree of conformational disorder at elevated temperatures.
authors.affiliation: Fakultät für Chemie and Center for Nanointegration (CENIDE), Universität Duisburg-Essen, D-45117 Essen, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Weber
authors.affiliation: Fakultät für Chemie and Center for Nanointegration (CENIDE), Universität Duisburg-Essen, D-45117 Essen, Germany.
authors.forename: Andre
authors.initials: A
authors.lastname: Beier
authors.affiliation: Fakultät für Chemie and Center for Nanointegration (CENIDE), Universität Duisburg-Essen, D-45117 Essen, Germany.
authors.forename: Eckart
authors.initials: E
authors.lastname: Hasselbrink
authors.affiliation: Fakultät für Chemie and Center for Nanointegration (CENIDE), Universität Duisburg-Essen, D-45117 Essen, Germany.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Balgar