J. Phys. II France
Volume 7, Numéro 10, October 1997
Page(s) 1337 - 1351
DOI: 10.1051/jp2:1997190
J. Phys. II France 7 (1997) 1337-1351

A Single Director Switching Mode for Monodomain Liquid Crystal Elastomers

Philip M.S. Roberts, Geoffrey R. Mitchell and Frederick J. Davis

Polymer Science Centre, JJ Thomson Physical Laboratory, University of Reading, Reading, Berkshire, RG6 6AF, UK

(Received 27 April 1997, received in final form 18 June 1997, accepted 27 June 1997)

We report rotation of a single director in a nematic monodomain, acrylate based side-chain elastomer which was subjected to mechanical fields applied at angles in the range $80^{\circ} - 90^{\circ}$ to the director, ${\bf n}_0$, present at the time of network formation. Time and spatially resolving wide angle X-ray scattering, together with polarised light microscopy measurements revealed a pronounced, almost discontinuous switching mode at a critical extension as the strain was applied at angles approaching $90^{\circ}$ to ${\bf n}_0$, whereas a more continuous rotation was seen when the strain was applied at more acute angles. This director reorientation was more or less uniform across the complete sample and was accompanied by a modest decrease in orientation parameter $\langle P_2\rangle$. At strains sufficient to induce switching there was some continuous distribution of director orientations with fluctuations of $\pm$10 $^{\circ}$ although there was no evidence for any localised director inhomogenities such as domain formation. The observed deformation behaviour of these acrylate-based nematic monodomains was in accord with the predictions of a theory developed by Bladon et al., in that the complete set of data could be accounted for through a single parameter describing the chain anisotropy. The experimentally deduced chain anisotropy parameter was in broad agreement with that obtained from small-angle neutron scattering procedures, but was somewhat greater than that obtained by spontaneous shape changes at the nematic-isotropic transition.

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