INFLUENCE OF IONS ON THE CRITICAL-BEHAVIOR OF A BINARY MIXTURE NEAR THE CONSOLUTE POINT

The lower critical point of stratification of a 3-methylpyridine (MP) + heavy water (D2O) mixture in the presence of Na+ and Cl- ions has be en studied by the Toepler shadow method. Addition of 0.3% ions lowered the critical temperature and reduced the equilibration time and the g radient of the refractive index (compressibillity). The analysis of th e form of the near-critical isotherm demonstrated the ionic mixture to be described by the index delta = 3.05 +/- 0.15, which corresponds to the classical mean-field theory. The results obtained provide evidenc e that even small admixtures of charged particles result in a substant ial suppression of fluctuations near the critical point by the long-ra nge Coulomb interaction.