Universal direction in thermoosmosis of a near-critical binary fluid mixture

We consider thermoosmosis of a near-critical binary fluid mixture, lying in the one-phase region, through a capillary tube in the presence of preferential adsorption of one component. The critical composition is assumed in the two reservoirs linked by the tube. With coarse-grained approach, we evaluate the flow field induced by the thermal force density. We predict a universal property; if the mixture is near the upper (lower) consolute point, the flow direction is the same as (opposite to) the direction of the temperature gradient, irrespective of which component is adsorbed onto the wall.