The University of Southampton
University of Southampton Institutional Repository

Field-induced alignment of a smectic-A phase: a time-resolved x-ray diffraction investigation

Field-induced alignment of a smectic-A phase: a time-resolved x-ray diffraction investigation
Field-induced alignment of a smectic-A phase: a time-resolved x-ray diffraction investigation
The field-induced alignment of a smectic-A phase is, in principle, a complicated process involving the director rotation via the interaction with the field and the layer rotation via the molecular interactions. Time-resolved nuclear magnetic resonance spectroscopy has revealed this complexity in the case of the director alignment, but provides no direct information on the motion of the layers. Here we describe a time-resolved x-ray diffraction experiment using synchrotron radiation to solve the challenging problem of capturing the diffraction pattern on a time scale which is fast in comparison with that for the alignment of the smectic layers. We have investigated the alignment of the smectic-A phase of 4-octyl-4'-cyanobiphenyl by a magnetic field. The experiment consists of creating a monodomain sample of the smectic-A phase by slow cooling from the nematic phase in a magnetic field with a flux density of 7 T. The sample is then turned quickly through an angle phi(o) about an axis parallel to the x-ray beam direction but orthogonal to the field. A sequence of two-dimensional small angle x-ray diffraction patterns are then collected at short time intervals. Experiments were carried out for different values of phi(o), and at different temperatures. The results show that the alignment behavior changes fundamentally when phi(o) exceeds 45degrees, and that there is a sharp change in the alignment process when the temperature is less than 3 degreesC below the smectic-A-nematic transition. The results of the x-ray experiments are in broad agreement with the NMR results, but reveal major phenomena concerning the maintenance of the integrity of the smectic-A layer structure during the alignment process.
liquid-crystal, shear
0021-9606
4397-4413
Bras, W.
e39a277c-1e6e-4535-b7d1-0f51956c7174
Emsley, J.W.
9d219d5e-28c0-4a8c-bf3d-1f78cd707c17
Levine, Y.K.
10ddb29b-f06e-4327-b7c0-d6e415747a58
Luckhurst, G.R.
7807d1c6-54a1-414f-9abe-22de4d9c30f7
Seddon, J.M.
029271d3-c2dd-4119-8455-d485bc4b5a74
Timimi, B.A.
845f8bba-a04b-4e8d-adfe-51b13e9f29ca
Bras, W.
e39a277c-1e6e-4535-b7d1-0f51956c7174
Emsley, J.W.
9d219d5e-28c0-4a8c-bf3d-1f78cd707c17
Levine, Y.K.
10ddb29b-f06e-4327-b7c0-d6e415747a58
Luckhurst, G.R.
7807d1c6-54a1-414f-9abe-22de4d9c30f7
Seddon, J.M.
029271d3-c2dd-4119-8455-d485bc4b5a74
Timimi, B.A.
845f8bba-a04b-4e8d-adfe-51b13e9f29ca

Bras, W., Emsley, J.W., Levine, Y.K., Luckhurst, G.R., Seddon, J.M. and Timimi, B.A. (2004) Field-induced alignment of a smectic-A phase: a time-resolved x-ray diffraction investigation. The Journal of Chemical Physics, 121 (9), 4397-4413. (doi:10.1063/1.1776116#).

Record type: Article

Abstract

The field-induced alignment of a smectic-A phase is, in principle, a complicated process involving the director rotation via the interaction with the field and the layer rotation via the molecular interactions. Time-resolved nuclear magnetic resonance spectroscopy has revealed this complexity in the case of the director alignment, but provides no direct information on the motion of the layers. Here we describe a time-resolved x-ray diffraction experiment using synchrotron radiation to solve the challenging problem of capturing the diffraction pattern on a time scale which is fast in comparison with that for the alignment of the smectic layers. We have investigated the alignment of the smectic-A phase of 4-octyl-4'-cyanobiphenyl by a magnetic field. The experiment consists of creating a monodomain sample of the smectic-A phase by slow cooling from the nematic phase in a magnetic field with a flux density of 7 T. The sample is then turned quickly through an angle phi(o) about an axis parallel to the x-ray beam direction but orthogonal to the field. A sequence of two-dimensional small angle x-ray diffraction patterns are then collected at short time intervals. Experiments were carried out for different values of phi(o), and at different temperatures. The results show that the alignment behavior changes fundamentally when phi(o) exceeds 45degrees, and that there is a sharp change in the alignment process when the temperature is less than 3 degreesC below the smectic-A-nematic transition. The results of the x-ray experiments are in broad agreement with the NMR results, but reveal major phenomena concerning the maintenance of the integrity of the smectic-A layer structure during the alignment process.

Full text not available from this repository.

More information

Published date: 1 September 2004
Keywords: liquid-crystal, shear

Identifiers

Local EPrints ID: 20145
URI: https://eprints.soton.ac.uk/id/eprint/20145
ISSN: 0021-9606
PURE UUID: 97d54c23-179f-4fee-b288-19770f32d93d

Catalogue record

Date deposited: 22 Feb 2006
Last modified: 15 Jul 2019 19:26

Export record

Altmetrics

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

Atom RSS 1.0 RSS 2.0

Contact ePrints Soton: eprints@soton.ac.uk

ePrints Soton supports OAI 2.0 with a base URL of https://eprints.soton.ac.uk/cgi/oai2

This repository has been built using EPrints software, developed at the University of Southampton, but available to everyone to use.

We use cookies to ensure that we give you the best experience on our website. If you continue without changing your settings, we will assume that you are happy to receive cookies on the University of Southampton website.

×