Exploration of crossover criticality in an aqueous electrolyte solution

The light scattering measurements that yield the osmotic susceptibility (chi(T)) in a ternary liquid mixture of 3-methylpyridine + water + sodium bromide are presented. The measurements have been performed in the one-phase region near the lower consolute points T-L's of samples with different concentrations (X) of NaBr. The data analysis has been performed by incorporating both one and two correction-to-scaling terms. Results indicate that for large concentrations of NaBr, two correction-to-scaling terms are necessary for a proper description of the data. Moreover, it is observed that the amplitude of the first correction-to-scaling term (chi(1)) is negative for all the cases studied. These results are interpreted as a nonmonotonic crossover of the effective susceptibility exponent, gamma(eff), from its Ising value of 1.24 to the mean-field value of 1.00, when moving away from a given T-L. Investigations on the existence of an additional length scale in this mixture, using excess molar volume measurements, are also reported. (C) 2002 Elsevier Science B.V. All rights reserved.