Novel phase-transition behavior in an aqueous electrolyte solution

• Published in: International journal of thermophysics 2000-11, Vol.21 (6), p.1321-1338
• Main Authors: JACOB, J, ANISIMOV, M. A, KUMAR, A, AGAYAN, V. A, SENGERS, J. V
• Format: Article
• Language: English
• Subjects: Binary mixtures; Chemistry; Composition effects; Exact sciences and technology; General and physical chemistry; Light scattering; Liquid-liquid equilibria; Nitrogen compounds; Phase equilibria; Phase interfaces; Phase transitions; Sodium compounds; Solutions; Water
• ISSN: 0195-928X; 1572-9567
• DOI: 10.1023/A:1006601325883

We have investigated the near-critical behavior of the susceptibility of a ternary liquid mixture of 3-methylpyridine, water, and sodium bromide as a function of the salt concentration. The susceptibility was determined from light-scattering measurements performed at a scattering angle of 90 degree in the one-phase region near the locus of lower consolute points. A sharp crossover from asymptotic Ising behavior to mean-field behavior has been observed at concentrations ranging from 8 to 16.5 mass% NaBr. The range of asymptotic Ising behavior shrinks with increasing salt concentration and vanishes at a NaBr concentration of about 17 mass%, where complete mean-field-like behavior of the susceptibility is observed. A simultaneous pronounced increase in the background scattering at concentrations above 15 mass%, as well as a dip in the critical locus at 17 mass% NaBr, suggests that this phenomenon can be interpreted as mean-field tricritical behavior associated with the formation of a microheterogeneous phase due to clustering of the molecules and ions. An analogy with tricritical behavior observed in polymer solutions as well as the possibility of a charge-density-wave phase is also discussed. In addition, we, have observed a third soap-like phase on the liquid-liquid interface in several binary and ternary liquid mixtures.