Methyl ethyl ketone+water+secondary butyl alcohol: a potential system for the exploration of a quadruple critical point.
We report preliminary experiments on the ternary-liquid mixture, methyl ethyl ketone (MEK)+water (W)+secondary butyl alcohol (sBA)--a promising system for the realization of the quadruple critical point (QCP). The unusual tunnel-shaped phase diagram shown by this system is characterized and visualized by us in the form of a prismatic phase diagram. Light-scattering experiments reveal that (MEK+W+sBA) shows near three-dimensional-Ising type of critical behavior near the lower critical solution temperatures, with the susceptibility exponent (gamma) in the range of 1.217< or =gamma< or =1.246. The correlation length amplitudes (xio) and the critical exponent (nu) of the correlation length (xi) are in the ranges of 3.536< or =xio < or =4.611 A and 0.619< or =nu< or =0.633, respectively. An analysis in terms of the effective susceptibility exponent (gammaeff) shows that the critical behavior is of the Ising type for MEK concentrations in the ranges of 0.1000< or =X< or =0.1250 and X> or =0.3000. But, for the intermediate range of 0.1750< or =X<0.3000, the system shows a tendency towards mean-field type of critical behavior. The advantages of the system (MEK+W+sBA) over the system (3-methylpyridine+water+heavy water+potassium Iodide) for the realization of a QCP are outlined.
Madhavan Unni
P K
PK
Department of Physics, Indian Institute of Science, Bangalore 560 012, India. madhavan@physics.iisc.ernet.in