H. Weingartner et al., High-pressure liquid-liquid immiscibility in aqueous solutions of tetra-n-butylammonium bromide studied by a diamond anvil cell technique, J SOL CHEM, 28(4), 1999, pp. 435-446
By use of a diamond anvil cell, we show that at high pressures aqueous solu
tions of tetra-n-butylammonium bromide form a closed liquid-liquid immiscib
ility loop with a critical concentration of about 2.0 mol-kg(-1). We report
data for a near-critical isopleth, which describes the pressure dependence
of the upper and lower consolute points. At about 700 MPa and 373 K both c
onsolute points coincide to form a hypercritical point, which characterizes
the minimum pressure to achieve immiscibility. We show that this immiscibi
lity can be rationalized in terms of Fitter's ion-interaction theory. We de
termine the ion-interaction parameters of Fitter's theory up to 423 K at no
rmal pressure. Inclusion of volumetric data gives the correct trend toward
a high-pressure immiscibility. We discuss the results in terms of the inter
play between ionic and hydrophobic forces in this system.