From hidden shear-elasticity to opto-and thermo-elasticity in confined polymer melts and viscous liquids

From the newly identified low frequency liquid elasticity, it turns out the possibility to reveal novel dynamic properties of liquids at mesoscopic scale. We present two examples illustrating the impact of the mesoscopic liquid elasticity in optics and thermodynamics. We show strain induced optical effects and thermo-induced effects that occur in the liquid state and reveal the need to take into consideration the elastic character of fluids at small scale. The fluids are submitted to a low frequency (~ Hz) mechanical shear strain (external stress). We probe the dynamic response by two methods, either accessing instant optical response of the liquid phase of liquid crystals and or probing the thermal response upon mechanical deformation. It is shown that the isotropic phase of liquid crystals can exhibit a dynamic birefringence in the isotropic phase while ordinary liquids exhibit cold and cold thermal waves upon low frequency excitation