LIGHT-SCATTERING INVESTIGATIONS OF THE LIQUID-LIQUID PHASE-TRANSITIONOF THE IONIC SYSTEM - TRIMETHYLETHYL-AMMONIUM BROMIDE IN CHLOROFORM

Phase diagrams and light-scattering measurements of solutions of trime thylethyl-ammonium bromide in chloroform (epsilon=4.72 at 25 degrees C ) with an ethanol content of 1% are reported. The system has a lower c ritical point near T=25 degrees C. The critical mole fraction is x(c)= 0.0503+/-0.0002, which corresponds to the reduced variables T-c=0.036 and C-c=0.029 of the restricted primitive model (RPM) and is slightl y below the values predicted by the RPM for the critical parameters. T he analysis of the scattering intensity at critical composition gives nu=0.621+/-0.003 for the critical exponent of the correlation length x i with an amplitude of xi(0)=0.87+/-0.01 nm. The system, a solution of a salt of essentially spherical ions of almost equal size in a simple low-dielectric polar liquid, with critical parameters very close to p redictions of the RPM, nevertheless has an Ising critical point.