Interdigitation of an intercalated surfactant bilayer

Venkataraman, NV and Vasudevan, S (2001) Interdigitation of an intercalated surfactant bilayer. In: Journal of Physcial Chemistry B, 105 (32). pp. 7639-7650.

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Abstract

The cationic surfactant cetyltrimethylammonium (CTA) has been ion-exchange intercalated from an aqueous solution of the surfactant by a two-step process into the galleries of layered cadmium thiophosphate to give cd(0.83)PS(3)(CTA)(0.34). Two phases of the intercalated product are observed. One is a phase characterized by a lattice expansion of 26.5 Angstrom, in which the methylene chains of the CTA ion adopt a tilted bilayer arrangement. This phase, when left in the reaction media, transforms to a phase characterized by a lattice expansion of: 12.5 Angstrom with no change in chemical stoichiometry. Using X-ray diffraction and orientation-dependent infrared spectroscopy, it has been possible to establish that the observed collapse of the Interlayer spacing is a consequence of the interdigitation of the methylene "tails" of the intercalated CTA ion. Infrared, Raman, and C-13 NMR spectroscopies have been used to establish the conformation of the methylene chains in the intercalated normal bilayer and interdigitated bilayer phases of Cd0.83PS3(CTA)(0.34) and the dispersion of the delocalized methylene wagging (nu (3)) and rocking-twisting (nu (8)) modes as a probe of the planarity of the chains. The results indicate that a majority of the methylene chains in the intercalated interdigitated bilayer adopt an all-trans planar conformation, whereas, in the normal bilayer phase of Cd0.83PS3(CTA)(0.34), although a majority of the methylene units are in a trans configuration, the presence of a few gauche defects is sufficient to destroy the planarity of the methylene chain. Planarity of the methylene chains is the key factor for the absence or occurrence of interdigitation of the intercalated surfactant bilayer.

Item Type:	Journal Article
Publication:	Journal of Physcial Chemistry B
Publisher:	American Chemical Society
Additional Information:	Copyright of this article belongs to American Chemical Society.
Keywords:	Normal-Alkyl Chains;H Stretching Modes;Solid-State Nmr;Phosphatidylcholine. Bilayers;Conformation;Motion;Phase;Spectroscopy;Membranes;Molecules
Department/Centre:	Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited:	26 Aug 2009 12:34
Last Modified:	19 Sep 2010 04:55
URI:	http://eprints.iisc.ac.in/id/eprint/17098

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