Impact of Pressure on Low-Molecular Weight Near-Critical Mixtures of Limited Miscibility

Abstract

Near-critical mixtures of limited miscibility are significant for chemical physics, soft matter physics, and a variety of challenging applications. Their basic properties can be tuned by compressing or a systematic change of one of the components. This report addresses these issues, based on experimental studies in nitro-compound (nitrobenzene, o -nitrotoluene, and 1-nitropropane) and n -alkane (from pentane to eicosane) critical mixtures. Studies reveal new patterns for the evolution of the critical consolute temperature ( T C ) and concentration ( x C , mole fraction) within the tested homologous series: T C ( n ) ∼ n 2 and x C ( n ) ∼ n 1/2 . They also show two paths of the high-pressure impact: (i) d T C ( P )/d P > 0 and overlapping of normalized T C ( P ) dependences and (ii) the crossover d T C ( P )/d P < 0 → d T C ( P )/d P > 0 with increasing n -alkane length. The consistent parameterization of all T C ( P ) dependencies is introduced. Supplementary nonlinear dielectric effect studies indicate a possible molecular origin of the phenomenon. The coexistence curve under high pressure is in the agreement with the isomorphism postulate for critical phenomena but with a surprisingly strong distortion from the Cailletet–Mathias law of the rectilinear diameter. The new and reliable method for estimating the critical concentration and temperature is proposed. It explores the analysis of relative volumes occupied by coexisting phases.

The fluctuation-driven dielectric properties of liquid crystalline 8OCB and its nanocolloids

“…Derivative analysis of experimental data, supported by the effective exponent concept, 31 leads to the following relationship:where ϕ eff = ϕ + [(1 − α ) Aθ r ], θ r denotes the range of the fitted domain. 31…”

“…where the exponent b describes the leading term related to the order parameter. Derivative analysis of experimental data, supported by the effective exponent concept, 31 leads to the following relationship:…”

“…Ay r ], y r denotes the range of the fitted domain. 31 In ref. 30, the derivative-based analysis of pure 8OCB was applied for the so-called diameter d(T) = (1/3) e 8 (T) + (2/3) e > (T): f eff E 0.75 and then b E 1/4 was obtained.…”

Criticality-related fundamental bases for new generations of gas–liquid, liquid–liquid, and liquid (LE) extraction technologies

“…The simple extraction using a liquid carefully selected to the process target constitutes the simplest and probably the fundamental laboratory and industrial technology. It seems inherently free from any critical phenomena resulting from the Gibbs–Kohnstamm phase rule [ 42 ]. Pretransitional/precritical phenomena are coupled with continuous or weakly discontinuous phase transitions [ 11 ].…”

Pressing matter: why are ionic liquids so viscous?

“…High pressure might effectively raise the critical temperature of this mixture to above ambient temperatures, leading to undesirable phase separation. 56 Our solution to this problem was to optimise towards molecular mimics with low critical temperatures. To this end, promising molecular mimics were subjected to progressively lower temperatures (ambient temperature 20°C, fridge 5°C, freezer −20°C, dry ice −78°C).…”