Temperature Dependence of Molecular Motion in Smectic Liquid Crystals of Hydrated Sodium 4-(1′-Heptylnonyl)benzenesulfonate
The surfactant sodium 4-(1′-heptylnonyl)benzenesulfonate (SHBS), upon hydration to form a smectic liquid crystalline phase, exhibits a thermal transition of 1.62 ± 0.22 kcal per mole of SHBS centered at -70°C. From measurements of the temperature dependence of the carbon-13 NMR spectra and from the calorimetric studies, transition was identified as the freezing-in of motion of the aliphatic chains and can thus be labeled as the so-called gel-liquid crystal transition observed in phospholipids. The enthalpy and the entropy associated with the transition correspond to a change of approximately one trans-gauche rotation per hydrocarbon tail. A more intense, broad thermal transition with a heat of 15 ± 3 cal per gram of smectic phase is observed from ca. -10 to -50°C and shown to come primarily from the freezing-in of bilayer water. At ca. -23°C water associated with the ionic groups, as well as the motion of the SHBS head, becomes frozen-in. Several comparisons between SHBS and similar studies on synthetic phosphatidylcholine are made. © 1982 American Chemical Society.
F. D. Blum and W. G. Miller, "Temperature Dependence of Molecular Motion in Smectic Liquid Crystals of Hydrated Sodium 4-(1′-Heptylnonyl)benzenesulfonate," Journal of Physical Chemistry, American Chemical Society (ACS), Jan 1982.
The definitive version is available at http://dx.doi.org/10.1021/j100206a048
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© 1982 American Chemical Society (ACS), All rights reserved.