Dynamic light scattering and Freedericksz transistion in novel nematic liquid crystals
Dynamic light scattering and Freedericksz transistion in novel nematic liquid crystals
This thesis describes the implementation of two well-known experimental techniques, dynamic light scattering (DLS) and Freedericksz transition (FT), to measure the visco-elastic properties of a wide variety of nematic liquid crystalline systems.
After calibration, the DLS technique is applied to evaluate the visco-elastic parameters for a series of mixtures, which differ in their chemical nature and thus exhibit different optical anisotropies. Then, the values of k22 and γ1 are measured for mesogenic and non-mesogenic guest molecules added to a commercial host mixture in order to improve the in-plane switching mode.
In the next part, the influence of dichroic dopants on the visco-elastic constants and on the order parameter of the host is investigated for low concentrations of azo and anthraquinone dyes dissolved in 5CB. The temperature dependence of k11, k22 and γ1 is discussed for the series containing azo dye. The bend elastic constant and corresponding viscosity are determined for the anthraquinone dye guest-host samples. The data for the dichroic ratio and dye’s order parameter are also included for the two dyes.
The nematic materials, studied in the final section, are characterised by a dielectric anisotropy Δε, which changes sign either as a function of frequency or temperature. To illustrate the first case, mixtures of a novel phenylbenzoate compound in a neutral host are found to behave as ‘dual-frequency’ materials for a certain range of concentration. The dielectric, optical and visco-elastic properties are measured for the pure host mixture. The second case refers to mixtures of new symmetrical difluorobiphenyl bimesogens, characterised by low Δε. These dimers present improved switching for the flexoelectro-optic effect in short pitch chiral nematics.
University of Southampton
Schott, Cécile
bb97e03a-3cc3-4151-af1b-1d22f651494e
2002
Schott, Cécile
bb97e03a-3cc3-4151-af1b-1d22f651494e
Schott, Cécile
(2002)
Dynamic light scattering and Freedericksz transistion in novel nematic liquid crystals.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
This thesis describes the implementation of two well-known experimental techniques, dynamic light scattering (DLS) and Freedericksz transition (FT), to measure the visco-elastic properties of a wide variety of nematic liquid crystalline systems.
After calibration, the DLS technique is applied to evaluate the visco-elastic parameters for a series of mixtures, which differ in their chemical nature and thus exhibit different optical anisotropies. Then, the values of k22 and γ1 are measured for mesogenic and non-mesogenic guest molecules added to a commercial host mixture in order to improve the in-plane switching mode.
In the next part, the influence of dichroic dopants on the visco-elastic constants and on the order parameter of the host is investigated for low concentrations of azo and anthraquinone dyes dissolved in 5CB. The temperature dependence of k11, k22 and γ1 is discussed for the series containing azo dye. The bend elastic constant and corresponding viscosity are determined for the anthraquinone dye guest-host samples. The data for the dichroic ratio and dye’s order parameter are also included for the two dyes.
The nematic materials, studied in the final section, are characterised by a dielectric anisotropy Δε, which changes sign either as a function of frequency or temperature. To illustrate the first case, mixtures of a novel phenylbenzoate compound in a neutral host are found to behave as ‘dual-frequency’ materials for a certain range of concentration. The dielectric, optical and visco-elastic properties are measured for the pure host mixture. The second case refers to mixtures of new symmetrical difluorobiphenyl bimesogens, characterised by low Δε. These dimers present improved switching for the flexoelectro-optic effect in short pitch chiral nematics.
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Published date: 2002
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Local EPrints ID: 465011
URI: http://eprints.soton.ac.uk/id/eprint/465011
PURE UUID: 362e44dc-4cd8-4f0f-8faf-cd7a6829d4f2
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Date deposited: 05 Jul 2022 00:16
Last modified: 16 Mar 2024 19:53
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Author:
Cécile Schott
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