(P,T,x) Surface of liquid-liquid immiscibility in aqueous solutions of tetraalkylammonium salts

Abstract

Aqueous solutions of higher homologues of tetraalkylammonium salts exhibit liquid-liquid phase separation. A model study of the pressure-temperatureomposition (p,T,x) surface of immiscibility of tetraisopentylammonium bromide + H20 up to 370 K and 200 MPa yielded a closed miscibility gap at atmospheric pressure with its lower part suppressed by crystallization, and a very unusual hyperbolic shape of the p,T,x surface. The results reflect a very peculiar behavior of the thermodynamic excess functions of aqueous solutions of hydrophobic ions which is discussed in relation to known regularities in the thermodynamic properties of the lower homologues which are completely miscible with water. IntroductionSymmetrical quarternary ammonium salts (R4N+X-, where R stands for alkyl chains) form an interesting class of 1 : 1 electrolytes which are capable of subtle and nearly continuous structure variations. Thermodynamic aspects of their hydration and mutual

Phase Equilibria in Binary and Ternary Hydrothermal Systems

“…The loops may fi rst shrinks but do not disappear completely and even become wider again with pressure, as in the systems 4-methylpiperidine (C 6 H 13 N) -H 2 O and 3-methylpyridine (3-C 6 H 7 N)-D 2 O (Figure 1.19). Similar type of phase behavior was found in the system tetraisopentylammonium bromide (C 20 H 44 NBr) -H 2 O (Weingartner and Steinle, 1992), where the upper critical solution temperature (UCST), observed at 369.2 K and atmospheric pressure, displays a minimum in the pressure dependence at about 60 MPa. The low-temperature parts of the closed loops are suppressed by crystallization at around 303 K. The LCST was estimated by symmetrical extrapolation of the upper part of the gap to be about 273 K and shows a maximum in the pressure dependence.…”

Closed‐Loops of liquid‐liquid immiscibility in binary mixtures of equal sized molecules predicted with a simple theoretical equation of state

“…8.1 is a type VIIii (2'n). The subscript ''3' was introduced by Boshkov for the term "immiscibility island" [31]. In Fig.…”

Thermoresponsive Ionic Liquid/Water Mixtures: From Nanostructuring to Phase Separation

“…A paradigmatic study [ 31 ] in this area, analysed the miscibility gap of the alkyl-ammonium [N ][I] ILs in water. A preliminary study [ 104 ] considering [N ][I] ( ) also in water identified a UCST, but the shape of the coexistence curve suggested the presence of a related LCST, whose observation, however, was prevented by crystallisation. This picture was confirmed by measurements on an IL with the less symmetric cation ([N ] ), decreasing the freezing point and revealing the underlying LCST.…”