Agnieszka Siporska

Miscibility of Ionic Liquids with Polyhydric Alcohols

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 ILs 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.

Solvent H/D isotope effects on miscibility and Θ-temperature in the polystyrene–cyclohexane system

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.

Deuterium isotope effect on miscibility of acetone with hydrocarbons C10 to C20

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.