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Flexible dimers as dopants for liquid crystal display mixtures with faster relaxation times

Flexible dimers as dopants for liquid crystal display mixtures with faster relaxation times
Flexible dimers as dopants for liquid crystal display mixtures with faster relaxation times
A series of fluoro-substituted ?,?-bis-diphenyloxyalkanes have been investigated as possible dopants for nematic liquid crystal display mixtures to reduce the rotational viscosity and hence response times of the mixtures. The compounds have been prepared using the Williamson synthesis, and the effect of the dopants on the mesophase transition temperature of a suitable Merck display mixture host ( ZLI-4792) has been determined. Measurements of magnetic field-induced relaxation times for director reorientation have been made on the doped and undoped mixtures using a novel electron spin resonance ( ESR) method developed by some of the authors. The relationship between field-induced relaxation times and the rotational viscosity is explained and results are reported for the rotational viscosity of the host material. A brief discussion of the molecular theories of rotational viscosity of nematic liquid crystals identifies the important molecular factors as shape, size, flexibility and orientational order parameter. The influence of the dopant molecules on the orientational order parameter of the doped mixtures has been measured using a static ESR method, and these results enable the separate effects of the dopants on the order parameter of the host and on the rotational dynamics to be identified. Results for field-induced relaxation times and order parameters of doped mixtures are reported for seventeen ?,?-bis-fluoro-diphenyloxyalkane dopants. Additionally comparative results are reported for a structurally related compound 1,2-trans-di(4'-propylphenyl) 1',2'- difluoroethane. It is found that particular substitution patterns of fluorine atoms in the phenyl rings of the dopant compounds can result in shorter relaxation times for the nematic display mixture investigated. The use of flexible dimers as dopants provides an additional design aid in the development of nematic mixtures for applications.
active-matrix displays, rotational viscosity, physical-properties, dielectric-relaxation, nematogenic molecules, orientational order, statistical-theory, coefficients, systems, dependence
4675-4689
Araya, K.
5e4cec4b-82ce-47dd-b786-a86054bc2c94
Dunmur, D.A.
d10d31b4-e7ac-4a9d-9cfc-b53f1b1a35a7
Grossel, M.C.
403bf3ff-6364-44e9-ab46-52d84c6f0d56
Luckhurst, G.R.
7807d1c6-54a1-414f-9abe-22de4d9c30f7
Marchant-Lane, S.E.
eb7308d5-0347-4519-8de2-2b9ba915a6cb
Sugimura, A.
ad404617-1e0f-445f-84d4-1f7efdf57909
Araya, K.
5e4cec4b-82ce-47dd-b786-a86054bc2c94
Dunmur, D.A.
d10d31b4-e7ac-4a9d-9cfc-b53f1b1a35a7
Grossel, M.C.
403bf3ff-6364-44e9-ab46-52d84c6f0d56
Luckhurst, G.R.
7807d1c6-54a1-414f-9abe-22de4d9c30f7
Marchant-Lane, S.E.
eb7308d5-0347-4519-8de2-2b9ba915a6cb
Sugimura, A.
ad404617-1e0f-445f-84d4-1f7efdf57909

Araya, K., Dunmur, D.A., Grossel, M.C., Luckhurst, G.R., Marchant-Lane, S.E. and Sugimura, A. (2006) Flexible dimers as dopants for liquid crystal display mixtures with faster relaxation times. Journal of Materials Chemistry, 16 (48), 4675-4689. (doi:10.1039/b610598j).

Record type: Article

Abstract

A series of fluoro-substituted ?,?-bis-diphenyloxyalkanes have been investigated as possible dopants for nematic liquid crystal display mixtures to reduce the rotational viscosity and hence response times of the mixtures. The compounds have been prepared using the Williamson synthesis, and the effect of the dopants on the mesophase transition temperature of a suitable Merck display mixture host ( ZLI-4792) has been determined. Measurements of magnetic field-induced relaxation times for director reorientation have been made on the doped and undoped mixtures using a novel electron spin resonance ( ESR) method developed by some of the authors. The relationship between field-induced relaxation times and the rotational viscosity is explained and results are reported for the rotational viscosity of the host material. A brief discussion of the molecular theories of rotational viscosity of nematic liquid crystals identifies the important molecular factors as shape, size, flexibility and orientational order parameter. The influence of the dopant molecules on the orientational order parameter of the doped mixtures has been measured using a static ESR method, and these results enable the separate effects of the dopants on the order parameter of the host and on the rotational dynamics to be identified. Results for field-induced relaxation times and order parameters of doped mixtures are reported for seventeen ?,?-bis-fluoro-diphenyloxyalkane dopants. Additionally comparative results are reported for a structurally related compound 1,2-trans-di(4'-propylphenyl) 1',2'- difluoroethane. It is found that particular substitution patterns of fluorine atoms in the phenyl rings of the dopant compounds can result in shorter relaxation times for the nematic display mixture investigated. The use of flexible dimers as dopants provides an additional design aid in the development of nematic mixtures for applications.

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More information

Published date: 2006
Keywords: active-matrix displays, rotational viscosity, physical-properties, dielectric-relaxation, nematogenic molecules, orientational order, statistical-theory, coefficients, systems, dependence

Identifiers

Local EPrints ID: 44360
URI: https://eprints.soton.ac.uk/id/eprint/44360
PURE UUID: 393e6ff0-f350-41d1-8fea-51cb86210d5a
ORCID for M.C. Grossel: ORCID iD orcid.org/0000-0001-7469-6854

Catalogue record

Date deposited: 28 Feb 2007
Last modified: 14 Mar 2019 01:53

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