Propagating modes in a binary liquid mixture under thermal stress

Fabrizio Croccolo (1) , Loreto García-Fernández , Henri Bataller (2) , Alberto Vailati , José María Ortiz de Zárate

1 LFCR - Laboratoire des Fluides Complexes et leurs Réservoirs
2 TEFC - Thermodynamique et Energétique des fluides complexes

Nonequilibrium temperature and concentration fluctuations inside a binary liquid mixture under the action of a temperature gradient relax back to equilibrium either due to conduction and diffusion at large wave numbers, or due to the quenching determined by gravity at small wave numbers. We investigate the dynamics of nonequilibrium fluctuations in a binary liquid mixture of polystyrene and toluene heated from above under stationary conditions in a thermodiffusion experiment. We show that the strong gravitational stabilization at small wave numbers determines the appearance of propagating modes of nonequilibrium fluctuations as detected through the structure function of shadowgraph images. The propagating modes are the combined effect of temperature and velocity nonequilibrium fluctuations induced by the buoyancy force. The experimental results are in good agreement with a fluctuating hydrodynamics theroretical model including the coupling of fluctuations of velocity, temperature and concentration.

Domaines: Matière Molle [cond-mat.soft]

Fabrizio Croccolo, Loreto García-Fernández, Henri Bataller, Alberto Vailati, José María Ortiz de Zárate. Propagating modes in a binary liquid mixture under thermal stress. Physical Review E , 2019, 99 (1), ⟨10.1103/physreve.99.012602⟩. ⟨hal-02010092⟩