T. Narayanan

Reentrant phase transitions in multicomponent liquid mixtures

A comprehensive review of the recent developments regarding the phenomenon of reentrant phase transitions (RPT) in binary and multicomponent liquid mixtures is presented. This phenomenon has been observed in amazingly diverse systems. A brief account of the analytical efforts to model the reentrant miscibility - especially in the limit of vanishing reentrance marked by a double critical point (DCP) - is provided. A critical assessment of the initial experimental investigations concerning RPT is made and the factors which impede its proper understanding are identified. The approach to double criticality is rationalized by a crossover of the Ising-like critical exponents from their doubled to single limit, with the doubled region prevailing in the entire temperature range at DCP. A range of unexplored problems, which can be readily addressed by using reentrant multicomponent liquid mixtures, is discussed.

Exploration of a quadruple critical point in a quaternary liquid mixture

We report the preliminary findings concerning the nature of a quadruple critical point that evolves when two independent double critical points merge in a thermodynamic field space. This special critical point is realized in a quasibinary mixture of 3‐methylpyridine, water, heavy water, and KI. The critical behavior of osmotic susceptibility was deduced from the scattered intensity measurements at 90°. Our results suggest that the nature of a quadruple critical point is similar to that of a normal double critical point. In addition, we find that the significance of the leading correction‐to‐scaling term is markedly increased as a result of the presence of the salt (KI) in the system.

Observation of the doubling of critical exponents in reentrant phase transitions

Abstract Electrical resistance ( R ) measurements are reported for ternary mixtures of 3-methylpyridine, water and heavy water as a function of temperature ( T ) and heavy water content in total water. These mixtures exhibit a limited two-phase region marked by a loop size (Δ T ) that goes to zero as the double critical point (DCP) is approached. The measurements scanned the Δ T range 1.010°C ⩽ Δ T ⩽ 77.5°C. The critical exponent (θ), which signifies the divergence of ∂ R /∂ T , doubles within our experimental uncertainties as the DCP is reached very closely.

A new description regarding the approach to double criticality in quasi-binary liquid mixtures

Abstract Electrical resistance and phase diagram measurements are reported for reentrant liquid mixtures 3-methylpyridine + water + NaCl and 3-methylpyridine + water + heavy water respectively. The results are analyzed employing a new field variable - which allows for the description of the access to any point on the critical line - by the same universal exponent. This method is also in agreement with the doubling of the critical exponents near the double critical point, using the conventional field variable z.sfnc;(Tc − T)/Tcz.sfnc;.

On the nature of extended scaling near the vanishing re-entrance

Abstract Light scattering investigations are reported in a re-entrant quasi-binary mixture of 3-methylpyridine (MP) +water (W) doped with NaCl. Our results reveal the shrinkage of a simple scaling region in the neighbourhood of a double critical point (DCP) as a consequence of the addition of NaCl. At DCP, both the leading and extended scaling exponents (γ and Δ) double from their normal Ising values (1.24 and 0.5, respectively).