Strain-Induced Violation of Temperature Uniformity in Mesoscale Liquids

Abstract: Thermo-elasticity couples the deformation of an elastic (solid) body to its temperature and vice-versa. It is a solid-like property. Highlighting such property in liquids is a paradigm shift: it requires long-range collective interactions that are not considered in current liquid descriptions. The present pioneering microthermal studies provide evidence for such solid-like correlations. It is shown that ordinary liquids emit a modulated thermal signal when applying a low frequency (Hz) mechanical shear stress. The liquid splits in several tenths microns wide thermal bands, all varying synchronously and separately with the applied stress wave reaching a sizable amplitude of $\pm$ 0.2 {\deg}C. This thermal property is unknown in liquids. Thermo-mechanical coupling challenges a dogma in fluid dynamics: the liquid responds collectively, adapts its internal energy to external shear strain and is not governed by short relaxation times responsible of instant thermal dissipation. The proof of thermomechanical coupling opens the way to a new generation of energy-efficient temperature converters.