Nonequilibrium phase transitions in extreme conditions: effects of shear flow and heat flow

Abstract

Phase transitions in fluids can be drastically altered by shear flow and heat flow. We briefly discuss the mechanisms of shear effects in three very different fluids. They are near-critical fluids, semidilute polymer solutions in theta solvent, and highly supercooled liquids. As regards heat flow problems, we consider near the superfluid transition, which is extremely sensitive to heat flow and gravity in the vicinity of the -point. In particular, heat flow applied from above and gravity give rise to competing effects, producing unique nonequilibrium states, in which the temperature gradient and the transition temperature gradient under gravity cancel. (i) In a normal-fluid state, the resultant temperature difference can be extremely small and can even be of order 1 nK. (ii) When a superfluid region expands upward into a normal-fluid region, we conjecture that the superfluid velocity approaches a critical velocity, leading to dense generation of vortices whose role is to produce a temperature gradient equal to .