title: Conformational disorder in alkylsiloxane monolayers at elevated temperatures.
abstract: Vibrational sum frequency generation spectroscopy is used to characterize octadecylsiloxane monolayers on glass substrates at ambient conditions with a focus on thermally induced conformational disorder. Different modes of the C-H stretching vibrations of the terminal methyl groups and the methylene groups are therefore monitored in the frequency range of 2850-3000 cm(-1). We observe a progressive increase of conformational disorder of the alkyl chains due to gauche defects over the temperature range from 300 to 510 K. The conformational disorder is reversible over a temperature range from 300 to about 410 K. But after heating to temperatures above 410 K, order is not reestablished on the time scale of the experiment. These results suggest that the assumption of an all-trans configuration of the alkyl chains is an over-simplification which increasingly misrepresents the situation for elevated temperatures which are still well below the one at which decomposition starts.
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: Thorsten
authors.initials: T
authors.lastname: Balgar
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
mesh_terms: D004355:Drug Stability; D008968:Molecular Conformation; D012833:Siloxanes / Q000737:chemistry*; D013696:Temperature; D014732:Vibration
chemical_list: D012833:Siloxanes