Calix-CSARevised.doc - On the layer structures in acid and amine-substituted calixarene Langmuir-Blodgett films C M McCartneya N Cowlama F Davisb T

Calix-CSARevised.doc - On the layer structures in acid and...

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On the layer structures in acid- and amine-substituted calixarene Langmuir-Blodgett films. C. M. McCartney a , N. Cowlam a , F. Davis b* T. Richardson a ( dec .), A. Desert c , A. Gibaud c , and C. J. M. Stirling d . a Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH, U.K. b Current address Cranfield Health, Cranfield University, Cranfield, MK43 0AL, U.K. c Laboratoire P.E.C. Rayons-X, Faculté des Sciences, Université du Maine, 72085 Le Mans Cedex 9, France. d Department of Chemistry, University of Sheffield, Sheffield, S3 7HF, U.K. Abstract X-ray reflectometry measurements have been made on Langmuir–Blodgett (LB) films of an amine-substituted tertiary octyl calix[8]arene and of alternating layers of acid and amine- substituted tertiary octyl calix[8]arene as well on LB films of alternating layers acid/amine- substituted tertiary butyl calix[4]arenes. The total film thickness and the bilayer spacing were obtained for each sample from its reflectivity profile R(Q) v. Q . Simulations of the reflectivity profiles were made with a program based on Parratt's recursive relations, using models of their multilayer structures. The “pinched loop” molecular conformation which, rather surprisingly, describes the layer structure in an acid substituted tert-octyl calix[8]arene, also describes the structures in the amine-substituted and the alternate layer acid/amine-substituted calix[8]arenes, with the exception that the amine head-groups are larger and their interpenetration is prevented. In contrast, the smaller calix bowl in the acid/amine-substituted calix[4]arene molecules defines their conformation more rigidly. The layer structure of the alternate layer acid/amine-substituted calix[4]arene sample is therefore well described by the repetition of the classical bowl and chain configuration. Keywords. X-ray Reflectometry; Calixarene; LB film; Pinched loop *Corresponding author. Phone +44(0)1234 758332. Fax. +44(0)1234 758300. Email: [email protected]
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1. Introduction The general characteristics of the calix[4]resorcinarenes and the calixarenes [1] have been described in our previous papers on the layer structures in a calix[4]resorcinarene film [2, 3] and in a Langmuir-Blodgett (LB) film of an acid-substituted tertiary octyl calix[8]arene [4]. These compounds are of interest in host-guest chemistry and also as pyroelectric materials [5, 6] for use in thermal detectors and thermal imaging devices. LB films can be fabricated by the repetition of non-centrosymmetric molecular bilayers, which usually have a low permittivity and a low dielectric loss tangent. The classical fatty acid/fatty amine systems have often been studied in the past, but functionalised calixarenes can also be incorporated into alternate layer LB films. They exhibit a high density of acid/amine pairs and a high melting point for the completed film. Pyroelectric coefficients of up to 15 Cm -2 K -1 with figures of merit of F D . = 75 Cm -2 K -1 have been reported for calixarene based films [7], which are amongst the highest values of any LB films.
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