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Complex Liquid Crystal Phases in Cylindrical Confinement

Zhang, Ruibin (2012) Complex Liquid Crystal Phases in Cylindrical Confinement. PhD thesis, University of Sheffield.

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Abstract

Confined liquid crystals (LCs) have attracted much interest because their richness in physical phenomena and potential applications. In this thesis the configuration of novel liquid crystal phases confined in cylindrical cavities from tens of nanometres to hundred of microns primarily were investigated by means of small angle X-ray scattering (SAXS), grazing incident X-ray scattering (GSAXS) and atomic force microscopy (AFM). The arrangement of honeycomb phases and 3-d channeled-layer phases (ChL) formed by polyphilic side-branched compounds in nanoporous anodic aluminium oxide (AAO) templates as well as in glass capillaries with micrometer diameters were investigated. 3-d diffraction patterns were reconstructed from the SAXS data. A fracture method associated with AFM observation was performed on the AAO samples to complement the X-ray study. Details of assembly of individual columns inside the nanochannel were directly observed by AFM for the first time. Surprisingly, even the planar-anchored columns were found reluctant to orient axially (parallel to the 1-d channel), which was explained by the strong deformation energy of the 2-d lattice. Besides, the in-plane orientation of the 2-d lattice was observed in both planar and homeotropic anchoring conditions and different mechanisms were proposed. For the ChL phase, axial orientation was observed due to the high rigidity of the columns. The 3-d layered structure could be suppressed by the nanopores and an induced smectic structure was observed. Configuration of several discotic columnar LCs in cylindrical confinement was studied. The investigation of pure triphenylene derivatives in nanopores refutes the only detailed experimental work on discotics published as far. Again the discotic columns are mainly perpendicular to the channel axis, even with planar anchoring condition, to avoid the distortion of the 2-d lattice. The axial configuration was observed only when the rigidity of the columns was increased by dopant. The structure of LC-directed mesoporous silica nanofibers fabricated via dual structure-directing agents in 200 nm AAO membranes was characterized by SAXS and TEM. Different mesoporous structures were observed when changing the alkyl chain length of the cationic surfactant.

Item Type: Thesis (PhD)
Academic Units: The University of Sheffield > Faculty of Engineering (Sheffield) > Materials Science and Engineering (Sheffield)
Depositing User: Mr Ruibin Zhang
Date Deposited: 12 Dec 2012 10:35
Last Modified: 08 Aug 2013 08:51
URI: http://etheses.whiterose.ac.uk/id/eprint/3174

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