Research Projects

This project is aimed at discovering/realizing the Quadruple Critical Point (QCP) in ternary aqueous ketonic systems by using trace amounts of Ionic Liquids as the impurity. A QCP is generated when four critical points are made to coalesce to a single point in an appropriate thermodynamic field space in ternary/quaternary systems. Discovering the QCP is very important since, at QCP all the critical exponents are expected to quadruple from their values at isolated critical points. This means, that in multicomponent-liquid mixtures, the 3D-Ising critical exponent corresponding to the correlation length of critical concentration fluctuation (ξ) is expected to be ν=2.52 instead of its value of 0.63 at an isolated critical point. For a typical correlation length amplitude (ξ₀) of say ~ 1Å, close to the QCP (such that the reduced temperature distance is t ≤ 10^(-4) the correlation length of concentration fluctuations given by ξ=ξ₀ t^(-ν) grows to be as big as ~ 1m! with the life time of critical concentration fluctuations (τ_ξ ) becoming as large as ~ 10¹⁵ h. If this were possible then macroscopic observations and quantitative studies of the morphology of critical fluctuations and its fractal dimensions can be performed. In addition to this, at a QCP the weak critical exponents can be determined to a much higher level of accuracy than that possible at an isolated critical point. The large values of ξ attained at the QCP also competes with the size of the sample-cell itself enabling exploration of finite-size effects on the critical phenomena displayed by the system. This is the main scientific rationale for the project. We point out that an actual QCP has not been realized by any group of researchers so far. Our group has done detailed experimental studies on aqueous ketonic system: Methyl Ethyl Ketone (MEK)+ Water(W) + secondary Butyl alcohol (sBA) and Cyclopentanone (CP)+ Water(W) + secondary Butyl Alcohol (sBA), wherein we engineered the phase diagram of the system by addition of KSCN as impurity and successfully reduced the diameter of the critical-tunnel, pinch it out into two paraboloid critical lines with Double Critical Points at the vertices and control the distance between the vertices of the paraboloids. However we could not realize the QCP on account of the chemical complexity displayed by the system [Santhi Krishna et al., J. Mol. Liq. 383, 122814(2023);Naseer et al, J. Mol. Liq. 383, 122081(2023); Naseer et al, J. Mol. Liq. 296, 111776 (2019)]. In this project we plan to engineer the coexistence surface in MEK + W + sBA and CP + W + sBA using suitable ionic liquids, constrict the critical tunnel to realise the QCP and thereafter perform static laser light scattering experiments on samples near isolated critical point, double critical point, critical end point and the QCP in the system to elucidate the critical behavior of the system close to these critical points. The goal is to explore the critical behavior at the QCP and to test the prediction that the critical exponents get quadrupled at QCP. If successful we plan to extend the study further in the future and investigate the morphology of critical concentration fluctuations and also the detailed molecular interactions in the system through molecular dynamic simulations.