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

TL;DR

This study investigates how low-frequency shear mechanical fields influence the thermal equilibrium in mesoscopic liquids, revealing the emergence of shear-induced thermal waves and harmonics, and demonstrating the thermoelastic behavior of confined liquids.

Contribution

It provides experimental evidence of shear-induced thermal waves and harmonics in liquids, supporting theoretical models of thermoelasticity at mesoscopic scales.

Findings

Shear mechanical fields induce thermal waves in liquids.

Thermal harmonics develop with increased frequency or strain.

Liquid layers behave as thermoelastic media.

Abstract

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.