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

H Mendil (1) , P Baroni (1) , Laurence Noirez (1)

1 LLB - UMR 12 - Laboratoire Léon Brillouin

Recent studies have revealed that high molecular weight liquid crystals 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 rheo-SANS experiments, we show that the polymer chain is deformed at time scales longer than the viscoelastic relaxation time. Finally, careful visco-elastic measurements reveal a strong elastic behaviour; the melt is not a viscoelastic liquid but solid-like at equilibrium one hundred degrees over the glass transition temperature and up to 15°C over the Isotropic-Nematic phase transition. This supra molecular cohesion and its extra long relaxation times may explain the emergence of non-linear phenomena.

Mots clés: Shear elasticity; isotropic phase

Domaines: Matière Molle [cond-mat.soft]

H Mendil, P Baroni, Laurence Noirez. Unexpected giant elasticity in side-chain liquid-crystal polymer melts: A new approach for the understanding of shear-induced phase transitions. EPL - Europhysics Letters, 2005, 72 (6), pp.983-989. ⟨10.1209/epl/i2004-10552-3⟩. ⟨hal-01363182⟩