Thermoosmosis of a near-critical binary fluid mixture under preferential adsorption; Universal flow properties

Yabunaka, Shunsuke; Fujitani, Yohei*

We consider a binary fluid mixture, which lies in the one-phase region near the demixing critical point, to consider its dynamics through a capillary tube. We assume preferential adsorption of one component on the tube's wall due to short-range interactions. The resultant adsorption layer becomes very thick near the critical point, inside which the thermal force density under a temperature gradient is nonvanishing. This enables a temperature difference to cause the total mass flow of the mixture, which represents thermoosmosis. We predict that, for any binary mixture near the critical point with the upper (lower) critical solution temperature, the direction of the total mass flow is the same as (opposite to) the temperature gradient, respectively.