Nonequilibrium critical phenomena

We discuss the nonequilibrium critical phenomena in liquids, and the models for these phenomena based on local equilibrium and extended scaling assumptions. Special situations are proposed for experimental tests of the theory. Near-critical steady and transient states are reviewed. In a near-critical steady state characterized by a temperature gradient, the theory predicts strong nonequilibrium fluctuations at very large length scales. Close to the critical point, this results in a nonlinear regime of heat conductivity. A transient nonequilibrium state triggered by a rapid and large spatially uniform perturbation of the critical liquid is considered. A step away from criticality generates a free field with strong and decaying correlations in initial state, while a step towards criticality initiates the increase of fluctuations and of their correlation at the large-scale edge of the critical range. The approach to equilibrium is characterized by an equilibration length λeq that depends on time t. The theory predicts a power-law approach of the temperature to the new equilibrium; the new critical exponents depend on whether the temperature is initially increased or decreased.