Phase diagram in cyclopentanone + water + secondary butyl alcohol and light scattering investigations near the LCST

Abstract

We report light scattering investigations and study of phase diagram in the system cyclopentanone (CP) + water (W) + secondary butyl alcohol (sBA), a more promising system for exploring the Quadruple Critical Point (QCP) as compared to methyl ethyl ketone (MEK) + W + sBA. Unlike in MEK + W + sBA [A. P. Naseer and P. K. M. Unni, J. Mol. Liq., 296, 111,776 (2019)], the diameter of the tunnel D≡TU-TL decreases from 66.626 K at XCP≡Xketone = 0.1000 to 24.926 K at Xketone = 0.2500 without addition of a fourth component. Our studies indicate that addition of only 0.0018 weight fraction of KSCN (i.e., 5% of the concentration of KSCN required in case of the system MEK + W + sBA), is sufficient to split the tunnel-like portion into two paraboloids with an intervening one-phase region in between. The tunnel-like feature in the phase diagram of CP + W + sBA occurs for 0.1000≤XCP≤0.2000 and for XCP>0.2000, the tunnel is open towards higher water weight fractions, though the critical line of UCSTs and LCSTs is continuous. Light scattering investigations show Fisher renormalization of the susceptibility exponent γ for 0.1750≤Xketone≡XCP≤0.2500 with a near complete renormalization observed for Xketone≡XCP = 0.2500 and normal Ising exponents observed for the region 0.1750>Xketone≡XCP>0.2500. Similarly, Ising-like behavior is observed at both low and high XCP weight-fractions while a tendency for mean-field behavior is observed for Xketone = 0.2500. Both these features appear generic to ternary systems involving (ketone + water + secondary butyl alcohol). The correlation length amplitude of critical concentration fluctuation ξ0 starts from a value of 6.5Å for XCP = 0.15 and saturates at 8.5Å in the range 0.175≤XCP≤0.350.