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Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets
Published on: May 15, 2017
Solid-state low temperature→middle temperature phase transition of linoleic acid studied by FTIR spectroscopy
Fuwei Pi1, Fumitoshi Kaneko, Makio Iwahashi
1Department of Chemistry, School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo 669-1337, Japan.
Abstract:
Temperature-dependent FTIR spectra of linoleic acid were measured over a temperature range of -80 to -30 °C to explore solid-state low-temperature (LT) → middle-temperature (MT) phase transition of linoleic acid. Band assignments were made mainly for the 900-760 cm(-1) region, where the bands due to cis-olefin group's ═C-H out-of-plane mode and the progression bands due to CH(2) rocking-CH(2) twisting modes are expected to appear. The structural evolutions during the LT → MT phase transition of linoleic acid were investigated by analyzing the progression bands with the simple-coupled oscillator model to elucidate the features of acyl chain influenced with two cis-C═C bonds linked through one CH(2) group. Structure changes in the LT → MT transition of linoleic acid were compared with those in the γ → α transition of oleic acid. It has been found that the former is rather localized around the cis-diene group, while the latter occurs in the larger portion between the cis-olefin group to the methyl end. It is also suggested that the conformational change in the cis-olefin group on the LT → MT transition is on a lesser scale than that on the γ → α transition.
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