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The systematic study of miscibility of polyethylene glycols (PEGs) of four average molecular weights equal to 200 a.m.u., 300 a.m.u., 400 a.m.u., and 600 a.m.u., with regular and deuterated benzene homologues has been presented. All systems show phase diagrams with upper critical solution temperatures (UCSTs). The miscibility of PEGs/benzene derivatives systems increases in the range: PEG/p-xylene > PEG/m-xylene > PEG/ethylbenzene > PEG/o-xylene > PEG/toluene. Deuterium substitution makes the miscibility of the investigated systems better and this finding is consistent with the Rabinovich concept. The miscibility isotope effects grow with the molar mass of polyethylene and the highest value has been obtained for toluene. The scaling equation and NRTL model have been used for describing the phase diagrams.

The liquid–liquid phase diagrams of 1-alkyl-3-methylimidazolium bis(trifluoromethyl)sulfonyl imides ([CnMIM][NTf2], n = 6,7,8) with C6H6 and C6D6 have been obtained. As the length of the alkyl chain decreases, the immiscible region is significantly enlarged and the phase diagram changes its shape from the most popular type that exhibits upper critical solution temperature to the “hourglass” type. The values of isotope effects on miscibility increase when the carbon chain length decreases and reach 4.4 K, 5.5 K, 7.1 K and even 50.1 K for n = 12,10,8,7, respectively.

Liquid−liquid miscibility temperatures as a function of composition have been determined experimentally for the binary systems formed by trihexyl(tetradecyl)phosphonium chloride with hexane, octane...

Cloud point measurements were made for binary systems of polystyrene (PS) + methyl acetate (MA) and polystyrene (PS) + selectively deuterated MA: CD3COOCH3 and CH3COOCD3 with three PS samples of Mw = 4.0 × 105, 2.0 × 106, and 13.2 × 106. All systems are characterized by the phase diagrams with upper and lower critical temperature. H/D isotope effects on miscibility for both selectively deuterated acetates are very large and appeared to be independent of the site of deuterium substitution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47:2140–2143, 2009

The liquid–liquid miscibility temperatures as a function of composition and deuterium substitution have been experimentally determined for the binary mixtures of 1-decyl-3-methylimidazolium bis(trifluoromethyl)sulfonyl imide, [C10MIM][NTf2], and 1-dodecyl-3-methylimidazolium bis(trifluoromethyl)sulfonyl imide, [C12MIM][NTf2] with benzene and toluene and their deuterated forms. All systems exhibit upper critical solution temperatures (UCSTs) and better miscibility for ionic liquids with longer alkyl chain. The interchange of benzene for toluene results in worse miscibility for [C10MIM][NTf2] and better for [C12MIM][NTf2]. Deuteration of the aromatics leads to better miscibility in each case. The sign of the isotope effect is in agreement with expectations and its value seems to be seriously affected by the neighborhood of the hypercritical state.

Liquid–liquid miscibility temperatures as a function of composition and deuterium substitution have been experimentally determined for binary mixtures of aniline and cyclohexane and their various deuterated forms: aniline-d2, aniline-d5, cyclohexane-d12. In all cases studied, the deuteration leads to the upward shift of the upper critical solution temperature. This effect is discussed in the frame of the theory of the condensed phase isotope effects coupled with the phenomenological gE thermodynamic model of solutions.

The miscibilities of acetone and deuterated acetone with decane, tridecane, hexadecane, octadecane and eicosane over a broad concentration range have been determined. All the measured systems present phase diagrams with a visible asymmetry with respect to composition and are characterized by the upper critical solution temperature (UCST). It appears that deuterium substitution in acetone leads to the significant upward shift of UCST, increasing the domain of the limited miscibility. The phase diagrams were described by using a scaling equation with a critical exponent β close to the theoretically predicted one and practically independent of isotope substitution and hydrocarbon chain length.

High-accuracy cloud-point temperatures for polystyrene–cyclohexane (PS–CH) and polystryrene–deuterated cyclohexane (PS–CH-d) solutions were measured over a broad range of molecular weights: 2.5 × 104 ≤ Mw ≤ 1.32 × 107. All polystyrene samples were characterized by low polydispersity indexes. Deuterium substitution in cyclohexane shifts the UCSTs to higher values and this isotope shift increases with increasing molecular weight, reaching at the limit of infinite Mw the value 4.53 K. No isotope effect on the critical concentration has been detected. Using different methods, Θ-temperatures for both PS–CH and PS–CH-d systems were determined. All approaches generate consistent results and a remarkable isotope effect on the Θ-temperature is observed. It is shown that isotopic shifts on UCST and Θ-temperature translate as a red shift of the C–H stretching frequency of cyclohexane on its transfer from a pure liquid to polymer solution at infinite dilution. The effect of pressure on the Θ-temperature has also been analyzed and it appears to mimic that of the pressure dependence of the critical temperatures of polystyrene–cyclohexane solution. It is also shown that the frequency shift of C–H vibrations changes with pressure in a similar fashion.

The miscibility of isobutyric acid with water and the influence of the isotope substitution of oxygen (16O/18O) in water over a broad concentration range are reported. The system exhibits a phase diagram with an upper critical solution temperature (UCST) and a visible isotope effect thereon. The oxygen isotope substitution decreases the UCST, leading to better miscibility of isobutyric acid with water. The isotope shift, DeltaTc = Tc(18O) - Tc(16O), extrapolated to the 100% enrichment in 18O, is equal to -1.15 K; hence it is much smaller and opposite to that found for deuterium substitution. The origin of the observed miscibility isotope effect has been qualitatively discussed in terms of the condensed-phase isotope effect theory.

Liquid-liquid miscibility temperatures as a function of composition have been determined experimentally for the binary systems formed by ionic liquids ([bmim][BF(4)], [bmim][PF(6)], [emim][Tf(2)N], [bmim][Tf(2)N], [hmim][Tf(2)N]) and polyhydric alcohols (1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,2,3-propanetriol, 1,2-butanediol). The impact of ionic liquid and di- or three-hydroxy alcohol characteristics focusing on the effect of the IL's anion nature, cation alkyl chain length, and alcohol structure (number of hydroxyl groups, position of the hydroxy groups in the molecule, and number of carbon atoms in the diols) is presented. It appears that all systems exhibit upper critical solution temperatures. For dihydroxy alcohols mentioned above, miscibility with 1-butyl-3-methylimidazolium ionic liquids follows the order [BF(4)](-)[Tf(2)N](-)[PF(6)](-) and is dependent on the hydrogen-bond basicity of the anion. Analysis of these findings leads us to conclude that the miscibility of ionic liquids is likely related to the hydrogen-bond acceptor strength of the anion. Comparing the miscibility of 1,2-ethanediol with 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides, it can be seen that surprisingly, T(c)([emim](+))T(c)([bmim](+))T(c)([hmim](+)). This arrangement of critical temperatures is opposite to that observed earlier for systems with monohydroxy alcohols. Analyzing the influence of the polyhydroxy alcohol structure, we also noticed that the miscibility of the polyhydroxy alcohols with [bmim][Tf(2)N] or [bmim][BF(4)] decreases when the polarity of the alcohol rises.

The liquid-liquid miscibility temperatures as a function of composition and deuterium substitution have been experimentally determined for the binary mixtures of 1-butyl-3-methylimidazolium tetrafluroborate with 1-butanol, isobutyl alcohol, 2-butanol, and tert-butyl alcohol and their deuterated forms (OH/OD substitution). All systems exhibit upper critical solution temperatures (UCSTs) with a visible effect of branching in alcohols. Deuteration of alcohols in the hydroxyl group results in a decrease of the UCST of the given system and the largest shift is observed for tert-butyl alcohol. These solvent isotope effects nicely correlate with the polarity expressed by dielectric constants or E(T)(30) parameters of alcohols. The effect of the isotope substitution on the miscibility of ILs with butanols can be rationalized by using the statistical-mechanical theory of the isotope effects coupled with a phenomenological g(E) model. Following this procedure one finds that the isotope shift of UCST is associated mainly with the zero-point energy contribution.