Identification of Mechano-stimuli (Linear to Harmonic) Thermal Response in Mesoscopic Liquids

In the conventional picture, the temperature of a liquid bath in the quiescent state is uniform down to thermal fluctuation length scales. Here we examine the impact of a low frequency shear mechanical field (Hz) on the thermal equilibrium of liquids (Polypropylene glycol and pentadecane away from any phase transition) confined between high energy surfaces. We show the emergence of both cooling and heating shear waves of several tens microns widths varying synchronously with the applied shear strain wave. The thermal wave is stable at low strain amplitude and low frequency while thermal harmonics develop by slightly increasing the frequency or the strain amplitude. The liquid layer behaves as a thermoelastic medium. This view is in agreement with recent theoretical models predicting that liquids support shear elastic waves up to finite propagation length scale of the order the thermal wave.