Phonon-particle interactions and transport processes in liquids

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Abstract
The theory of thermal radiation forces is extended to the local interactions occurring among phonons and the material particles of a liquid, also in the absence of an external temperature gradient. In a solution, energy and momentum can be transferred by an impinging phonon to a particle, or the latter may perform work on the first, shifting it to a higher frequency. Upon time reversal, each of these elementary interactions commutes into the other. Isothermal diffusion, thermomechanical and mechanothermal effects in solutions can be interpreted within this unifying frame of reference. The density of the ‘‘gas’’ of thermal excitations, and the average of energy exchanged per interaction can be calculated from experimental data for common liquids. Nonequilibrium statistical mechanics and irreversible thermodynamics might be fruitfully revisited on the basis of the notion of phonon-particle interactions, since these are processes that occur at a more elementary level than the regression of fluctuations. Accordingly, the statistical approach proposed here may lead to a microscopic interpretation of Onsager’s reciprocity relations.