Molecular field theory of nematics composed of flexible molecules
Molecular field theory of nematics composed of flexible molecules
Many thermotropic liquid crystal molecules consist of flexible alkyl chains attached to rigid mesogenic groups, for example, the liquid crystal dimers in which two mesogenic groups are linked by a flexible spacer. The properties of these molecules, such as the nematic-isotropic transition temperatures and transitional entropy are found to depend on the length and parity of this flexible chain, and also the nature of the linkage between the mesogenic groups and spacer. These differences in properties can be understood at a simple level by considering the shape anisotropy of the molecules in their all-trans conformation. To represent the molecules in a single conformation ignores, however, the flexibility of the spacer which can adopt many configurations. Molecular field theories of flexible molecules give a semi-quantitative method of predicting the nematic-isotropic transitional properties, and here we use the Emsley-Luckhurst-Stockley theory of flexible molecules, our aim to gain an understanding of the effects of the molecular topology and the conformational distribution on the organisation occurring within the nematic phase, and its effect on the transitional properties.
To this end we have developed a model to represent the average shape of a dimer in the nematic and isotropic phases. The orientational distribution functions of the mesogenic groups and bonds in the flexible spacer of monomers and dimers, can also lead to another view of the organisation occurring within such systems. We have also calculated the transitional properties of symmetric and non-symmetric dimer series, in an attempt to reproduce the dependence on the spacer length of the difference between the average of the transition temperatures of the two parent symmetric dimers and that of the non-symmetric dimer. Finally we have derived a simple binary model of a mixture of a linear and a bent conformation, to aid in understanding of transitional properties of odd and even linked dimers.
University of Southampton
1994
Roskilly, Stephen
(1994)
Molecular field theory of nematics composed of flexible molecules.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Many thermotropic liquid crystal molecules consist of flexible alkyl chains attached to rigid mesogenic groups, for example, the liquid crystal dimers in which two mesogenic groups are linked by a flexible spacer. The properties of these molecules, such as the nematic-isotropic transition temperatures and transitional entropy are found to depend on the length and parity of this flexible chain, and also the nature of the linkage between the mesogenic groups and spacer. These differences in properties can be understood at a simple level by considering the shape anisotropy of the molecules in their all-trans conformation. To represent the molecules in a single conformation ignores, however, the flexibility of the spacer which can adopt many configurations. Molecular field theories of flexible molecules give a semi-quantitative method of predicting the nematic-isotropic transitional properties, and here we use the Emsley-Luckhurst-Stockley theory of flexible molecules, our aim to gain an understanding of the effects of the molecular topology and the conformational distribution on the organisation occurring within the nematic phase, and its effect on the transitional properties.
To this end we have developed a model to represent the average shape of a dimer in the nematic and isotropic phases. The orientational distribution functions of the mesogenic groups and bonds in the flexible spacer of monomers and dimers, can also lead to another view of the organisation occurring within such systems. We have also calculated the transitional properties of symmetric and non-symmetric dimer series, in an attempt to reproduce the dependence on the spacer length of the difference between the average of the transition temperatures of the two parent symmetric dimers and that of the non-symmetric dimer. Finally we have derived a simple binary model of a mixture of a linear and a bent conformation, to aid in understanding of transitional properties of odd and even linked dimers.
This record has no associated files available for download.
More information
Published date: 1994
Identifiers
Local EPrints ID: 458658
URI: http://eprints.soton.ac.uk/id/eprint/458658
PURE UUID: a8923b43-0b84-4d38-96a7-270ba861f21d
Catalogue record
Date deposited: 04 Jul 2022 16:53
Last modified: 04 Jul 2022 16:53
Export record
Contributors
Author:
Stephen Roskilly
Download statistics
Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.
View more statistics