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Polycatenar amphiphilic liquid crystals

Gainar, Adrian (2012) Polycatenar amphiphilic liquid crystals. MSc by research thesis, University of York.

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In order to study the effect on mesophase organisation of incorporating groups (hydrocarbon and fluorocarbon) that normally phase separate into the same liquid-crystalline molecules, a series of tri- and tetra-catenar mesogens has been prepared containing various combinations of hydrocarbon (CnH2n+1–: n = 12 or 14) and semiperfluorocarbon (CmF2m+1(CH2)4–; m = 8 or 10) chains. In addition, many of the intermediate compounds prepared en route were studied for their liquid crystal properties. The semiperfluorocarbon chains were added using Williamson ether chemistry with CmF2m+1(CH2)4Br, itself prepared via a radical addition of CmF2m+1I to 3-buten-1-ol to give a secondary iodide which was deiodinated in a radical process. Conversion of the alcohol to the bromide used HBr under phase-transfer conditions. The properties of the new compounds were elucidated using optical microscopy, differential scanning calorimetry and low-angle X-ray diffraction. The all-hydrocarbon compounds had been prepared previously and their mesomorphism was qualitatively identical to that of the all-semiperfluorocarbon analogues. However, when both hydrocarbon and semiperfluorocarbon chains were mixed in the same molecule, there was a significant change in behaviour as the mesogens organised themselves in order to maximise hydrocarbon-hydrocarbon and fluorocarbon-fluorocarbon interactions while minimising hydrocarbon-fluorocarbon interactions. For example, with tricatenar mesogens with a fluorocarbon chain at one end, this manifested itself as a doubling of the lamellar periodicity, while in unsymmetric tetracatenar mesogens, a reduction in phase symmetry from hexagonal (p6mm) to rectangular (p2gg) was seen along with a massive increase in lattice parameter.

Item Type: Thesis (MSc by research)
Keywords: polycatenar liquid crystals, amphiphilic, hydrocarbon chain, fluorocarbon chain, tetracatenar mesogen, tricatenar mesogen, segregation, powder X-ray diffraction, polarising optical microscopy, differential scanning calorimetry, Williamson reaction, smectic, nematic, columnar, smectic-to-columnar transition.
Academic Units: The University of York > Chemistry (York)
Depositing User: Dr. Adrian Gainar
Date Deposited: 04 Oct 2012 13:06
Last Modified: 08 Aug 2013 08:50
URI: http://etheses.whiterose.ac.uk/id/eprint/2791

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