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Melting of Saturated Fatty Acid Zinc Soaps

Barman, S and Vasudevan, S (2006) Melting of Saturated Fatty Acid Zinc Soaps. In: Journal of Physical Chemistry B, 110 (45). pp. 22407-22414.

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Abstract

The melting of alkyl chains in the saturated fatty acid zinc soaps of different chain lengths, $Zn(C_nH_{2n+1}COO)_2$; n = 11, 13, 15, and 17, have been investigated by powder X-ray diffraction, differential scanning calorimetry, and vibrational spectroscopy. These compounds have a layer structure with the alkyl chains arranged as tilted bilayers and with all methylene chains adopting a planar, all-trans conformation at room temperature. The saturated fatty acid zinc soaps exhibit a single reversible melting transition with the associated enthalpy change varying linearly with alkyl chain length, but surprisingly, the melting temperature remaining constant. Melting is associated with changes in the conformation of the alkyl chains and in the nature of coordination of the fatty acid to zinc. By monitoring features in the infrared spectra that are characteristic of the global conformation of the alkyl chains, a quantitative relation between conformational disorder and melting is established. It is found that, irrespective of the alkyl chain length, melting occurs when 30% of the chains in the soap are disordered. These results highlight the universal nature of the melting of saturated fatty acid zinc soaps and provide a simple explanation for the observed phenomena.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to American Chemical Society.
Department/Centre: Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited: 13 May 2008
Last Modified: 19 Sep 2010 04:44
URI: http://eprints.iisc.ernet.in/id/eprint/13961

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