CRITICAL-BEHAVIOR OF IONIC FLUIDS

We report the critical behavior of osmotic compressibility (chi(T)) that was deduced from turbidity, for two ionic fluid mixtures. The measurements covered the reduced temperature, t, range 7 X 10(-5) less than or equal to t less than or equal to 7 X 10(-2). The mechanism underlying the liquid-liquid phase separation is, predominantly, Coulombic in one case and solvophobic for the other. We find that the criticality of Coulombic phase separation is better described in terms of a crossover from mean field to Ising critical exponents, rather than true mean field exponents, as the critical temperature (T-c) is approached. In addition, we find that the critical phenomenon associated with the solvophobic phase separation in an ionic fluid is characterized by nonclassical critical exponents.