Thermodynamics of Phase Transitions in Langmuir Monolayers Observed by Vibrational Sum Frequency Spectroscopy
- 20 August 2003
- journal article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 125 (37) , 11166-11167
- https://doi.org/10.1021/ja036735w
Abstract
Vibrational sum-frequency spectroscopy (VSFS) was used to study gauche defects in octadecylamine (ODA) monolayers at the air/water interface. The VSFS spectra provide unique insights into phase transitions that occur as a result of changes in the structure of the monolayer's hydrophobic region. These changes can be attributed to the increased presence of gauche conformers in the ODA alkyl chains during the monolayer's transition from the solid to liquid phase. Temperature-dependent spectra from monolayers at several different pressures were used to assign the phase transition temperature based on the observed changes in microscopic structure. Through application of a two-dimensional form of the Clapeyron equation, the first in situ measurements of the entropy and enthalpy changes associated with gauche conformers in a monolayer were made.Keywords
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