Europhys. Lett.
Volume 72, Number 6, December 2005
Page(s) 983 - 989
Section Condensed matter: structural, mechanical and thermal properties
Published online 18 November 2005
Europhys. Lett., 72 (6), pp. 983-989 (2005)
DOI: 10.1209/epl/i2004-10552-3

Unexpected giant elasticity in side-chain liquid-crystal polymer melts: A new approach for the understanding of shear-induced phase transitions

H. Mendil, P. Baroni and L. Noirez

Laboratoire Léon Brillouin (CEA-CNRS), Ce-Saclay - 91191 Gif-sur-Yvette, France

received 9 December 2004; accepted in final form 18 October 2005
published online 18 November 2005

Recent studies have revealed that side-chain liquid-crystal polymers typically exhibit shear-induced phases within the isotropic melt. From rheo-birefringence measurements, we demonstrate that those shear-induced phases are not coupled with conventional orientational-order fluctuations. From viscoelastic measurements, we demonstrate that the melt is not liquid but gel-like one hundred degrees away from the glass transition temperature and up to $15\,^{\circ}$C away from the Isotropic-Nematic phase transition. Finally, rheo-SANS experiments show that the polymer chain is deformed at time scales compatible with this supra-molecular cohesion. The solicitation of this gel-like state explains the emergence of non-linear phenomena.

61.30.Vx - Polymer liquid crystals.
62.20.Dc - Elasticity, elastic constants.
61.30.Hn - Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions.

© EDP Sciences 2005