TURBIDITY, LIGHT-SCATTERING, AND COEXISTENCE CURVE DATA FOR THE IONICBINARY MIXTURE TRIETHYL N-HEXYL AMMONIUM TRIETHYL N-HEXYL BORATE IN DIPHENYL ETHER

We report turbidity, Light scattering, and coexistence curve data for a solution of triethyl n-hexyl ammonium triethyl n-hexyl berate in dip henylether. We recently reported that the present sample shows much hi gher turbidity than that of K. S. Zhang, M. E. Briggs, R. W. Gammon, a nd J. M. H. Levelt Sengers [J. Chem. Phys. 109, 4533 (1998)] for an ea rlier sample. An analysis of the data shows that nonclassical critical behavior is favored in the reduced temperature range from 10(-5) to 1 0(-2). At fixed reduced temperature, the correlation length is about t wice as large as that of the previous sample. The correlation length a mplitude calculated from the fit is 1.4 nm+/-0.1 nm. A detailed data a nalysis points out the limitations of turbidity measurements far away from the critical paint. The intensity of scattered light was measured at 90 degrees. Multiple scattering is relevant in the wider vicinity of the critical point and was corrected for by a Monte Carlo simulatio n method. An Ising-type exponent for the correlation length was obtain ed: nu = 0.641 +/- 0.003, and the amplitude of the correlation length xi(0)=1.34 nm+/-0.01 nm agrees with that of the turbidity experiment. Mean-held behavior can be ruled out. The refractive indices of coexist ing phases were measured in the reduced temperature range from t=10(-4 ) to 0.04. These measurements disagree with results reported by R. R. Singh and K. S. Fitter [J. Chem. Phys. 92, 6775 (1990)]. The present d ata lead to an exponent beta=0.34+/-0.01, close to the Ising value. Th e coexistence curve is much narrower than that of Singh and Fitter. Cr ossover could not be detected in any of the experiments. Two-scale-fac tor universality could be confirmed for this and another ionic system within the experimental uncertainty. (C) 1998 American Institute of Ph ysics. [S0021-9606(98)50344-3].