ABSTRACT
Recent experimental developments show that without reticulation links or entanglements, the isotropic phase of liquid crystals can work mechanically as an elastomer and optically as a harmonic oscillator at the sub-millimetre scale. The strength of the elastic response depends on the molecular architecture and is enhanced when the liquid-crystal molecules are attached as side-chain moieties to a chain backbone. This elastomeric behaviour of the isotropic phase is evidenced via stress and optical responses to a low-frequency mechanical excitation. Visible far away from any phase transition, this spectacular effect contains important information: the liquid state is a low threshold elastic medium; molecules are dynamically correlated and this elastic correlation is observed up to the sub-millimetre scale. This discovery sheds a new light on the origin of well-known effects as flow birefringence, shear banding in complex fluids or flow instabilities in simple liquids. The present paper emphasizes the key role of long range elastic interactions for a comprehensive approach to the flow birefringence, from its origins and to new possible applications.
Acknowledgements
The authors are grateful to P.A. Albouy and D. Petermann for their help for the X-Rays measurements, R&D Vision for adaptation of the trigger software and to F. Coneggo for discussions on analog electronics.
Disclosure statement
No potential conflict of interest was reported by the authors.