Scaling Equation of State for a Nonequilibrium Solution Under Gravity Close to Phase IInterface

Experimental investigations of equilibration kinetics for a methanol-hexane binary solution under gravity have been carried out at temperatures T below the critical consolute temperature, T < Tc , by using a refractometry technique. As a result of the experiment, both equilibrium nz(z, te) and nonequilibrium nz(z, t) height dependences of the refractive index gradient nz at different times t after the beginning of thermal equilibration have been obtained. Analysis of the data shows that the relaxation properties of the system at different fixed heights are determined not by a single relaxation time y(z), but by a spectrum of relaxation times Syi(zj, t). On the basis of the experimental data, the height dependence of the relaxation times has been analyzed for the studied solution in the course of its transition to equilibrium. The average relaxation time y(z) has been shown to decrease when nearing the phase iInterface (z=0). The relaxation time y(z, t) at a certain height z has been shown to also decrease when the system approaches an equilibrium state. A dynamic nonequilibrium equation of state has been proposed on the basis of the fluctuation theory of phase transitions for a substance under gravity close to the phase iInterface of a binary solution. It is based on the assumption that for small solution concentrations, (c−cc)/cc °1, every nonequilibrium height distribution nz(z, t) corresponds to an equilibrium distribution nz(z, DT) at a certain temperature DT=T−Tc . Here, cc is the critical concentration of the solution.