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Title: Adsorption and confinement effects in liquid crystals
Author: Mears, Laura Louise Elizabeth
ISNI:       0000 0004 5923 2025
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2015
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Three different types of liquid crystal have been studied under confinement within two novel sample environments. The thermotropic cyanobiphenyls 5CB and 8CB were also doped with both a core deuterated, fluorinated version of 110CB (F17) and the fully deuterated terphenyl d-5CT; their adsorption was measured using neutron reflectometry (NR). At the air/5CB interface, the adsorbed amount ofF17 decreased with increasing temperature within the nematic phase, it then remained constant in the isotropic with a small increase owing to nematic wetting at the surface. At the solid / nematic interface there was strong adsorption of F17 (4.9 ±0.9 mg m-2 ) with a fluorinated silane (PFDS) coating. There was negligible adsorption (0.4±0.2 mg m-2) for the hydrogenous (OTS) coated surface. In 8CB the F17 enhanced the surface smectic wetting at the fluorinated surface. NR was also used with a novel confinement cell. Both 8CB and 10CB were confined but showed no change in their structures and it appeared the 8CB nematic phase was squeezed out of the contact area. A surfactant, alcohol and D20 lyotropic system was also squeezed out under 1 bar of confinement for 80% water content, however, with 75% water the lyotropic remained in place with 1 bar of confinement. Phosphatidyl choline lipid bilayer stacks were the third liquid crystalline system to be confined. Despite the repeat distance, d, increasing for bilayers of DSPC and DPPC confined from the fluid (Lα phase and decreasing overall from the gel (Lβ1) phase, the same d was reached at 5 bar of confinement in both cases. Model fitting showed; for all lipid chain lengths, the lipid component increased in thickness and the water decreased, suggesting that the phase had changed. A confinement cell for use with X-ray reflection (XRR) and small angle X-ray scattering (SAXS) was designed and commissioned, through experiments on lipids and cyanobiphenyls. The reflectivity results were consistent with the NR results. SAXS was applied to a pair of planar aligned surfaces with a twist between the alignment directions. The decrease in thickness with applied confinement induced the twist grain boundary phase for angles between 68°and 90°. Hybrid alignment conditions showed a conversion from non-scattering to planar alignment with confinement
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available