Thermally perturbed barodiffusion in a binary liquid mixture

Abstract

In a binary liquid, the existence of a gravity-induced concentration gradient (the barodiffusion gradient) is a requirement for the system to be in equilibrium. In order to study the effect of forces which could drive such a system from equilibrium, we observe the long-time evolution of gravity-induced concentration gradients in the presence of small perturbing horizontal temperature gradients (\ensuremath{\leqslant} 85 mK/cm) in a system of aniline and cyclohexane near its critical point. These measurements are unique since previous studies of gravity-induced concentration gradients in binary liquids have focused only on fast developing gradients created by sedimentation or on the measurement of equilibrium barodiffusion. Our results reveal large variations in the steady state concentration gradients even in the absence of applied temperature gradients, suggesting that very small temperature gradients may cause significant fluctuations in a binary liquid system. Additionally, as the applied temperature gradient increases, the growth of the concentration gradients slows and fluctuations on time scales much shorter than the expected diffusion time appear.