Hydrocarbon chain conformation in an intercalated surfactant monolayer and bilayer

Cetyl trimethyl ammonium (CTA) ions have been confined within galleries of layered CdPS3 at two different grafting densities. Low grafting densities are obtained on direct intercalation of CTA ions into CdPS3 to give Cd0.93PS3(CTA)0.14. Intercalation occurs with a lattice expansion of 4.8 Å with the...

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Bibliographic Details
Published in:Journal of Chemical Sciences 2001-10, Vol.113 (5-6), p.539-558
Main Authors: Venkataraman, N. V., Vasudevan, S
Format: Article
Language:English
Subjects:
Bilayers
Grafting
Infrared spectroscopy
Intercalation
Ion exchange
Methylene
Molecular chains
Molecular conformation
Monolayers
NMR
Nuclear magnetic resonance
Single crystals
Surfactants
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Summary:Cetyl trimethyl ammonium (CTA) ions have been confined within galleries of layered CdPS3 at two different grafting densities. Low grafting densities are obtained on direct intercalation of CTA ions into CdPS3 to give Cd0.93PS3(CTA)0.14. Intercalation occurs with a lattice expansion of 4.8 Å with the interlamellar surfactant ion lying flat forming a monolayer. Intercalation at higher grafting densities was effected by a two-step ion-exchange process to give Cd0.83PS3(CTA)0.34, with a lattice expansion of 26.5 Å. At higher grafting densities the interlamellar surfactant ions adopt a tilted bilayer structure.13C NMR and orientation-dependent IR vibrational spectroscopy on single crystals have been used to probe the conformation and orientation of the methylene ‘tail’ of the intercalated surfactant in the two phases. In the monolayer phase, the confined methylene chain adopts an essentially all-trans conformation with most of the trans chain aligned parallel to the gallery walls. On lowering the temperature, molecular plane aligns parallel, so that the methylene chain lies flat, rigid and aligned to the confining surface. In the bilayer phase, most bonds in the methylene chain are in trans conformation. It is possible to identify specific conformational sequences containing a gauche bond, in the interior and termini of the intercalated methylene. These high energy conformers disappear on cooling leaving all fifteen methylene units of the intercalated cetyl trimethyl ammonium ion in trans conformational registry at 40 K.
ISSN:0253-4134
0974-3626
0973-7103
DOI:10.1007/BF02708789