Hydrodynamic study of 3-Methylpentane by transient grating experiments

Abstract

We report an optical heterodyne-detected transient grating experiment of glass-forming 3-methylpentane at different temperatures and wave vectors in the supercooled liquid range near the glass transition. We extract sound velocities, structural times and thermal diffusivities from fitting the spectra with a hydrodynamic model parametrizing the memory function of the viscosity with a stretched exponential.

Notes

† The electrostrictive effect produces at ‘zero’ time a non-zero longitudinal velocity that can be recognized in a HD-TG signal because it gives an oscillation with a phase of −90° with respect to the thermal contribution; that is, instead of an expansion where the interference of pump electric fields is in phase, there is a contraction at the maximum velocity.