Liquid-liquid phase separations and critical behavior of electrolyte solutions driven by long-range and short-range interactions

Critical behavior on approaching a special critical point in a complex fluid

The critical behavior of osmotic susceptibility is investigated in the re-entrant complex mixture 1-propanol (P)+water (W)+potassium chloride (KCl) through light-scattering measurements. The measurements are performed on approaching a special critical point [i.e., the double critical point (DCP)] in this mixture, along the line of upper critical solution temperatures (T(U)'s), by varying t from the high temperature one-phase region. The light-scattering data analysis emphasizes the need for corrections to the asymptotic Ising behavior and yields very large magnitudes for the correction-to-scaling amplitudes A(1) and A(2), with the first-correction amplitude A(1) being negative, signifying a nonmonotonic crossover behavior of the susceptibility exponent in this mixture. For the T(U) closest to the DCP, the effective susceptibility exponent gamma(eff) displays a nonmonotonic crossover from its nearly doubled three dimensional (3D)-Ising value toward its nearly double mean-field value with an increase in t. While for that far away from the DCP, it displays a nonmonotonic crossover from its single-limit Ising value toward a value slightly lower than its mean-field value of 1 with an increase in t. This feature of the effective susceptibility exponent is interpreted in terms of the possibility of a nonmonotonic crossover to the mean-field value from lower values in the nonasymptotic high t region. The renormalized Ising regime extends over a larger t range for the sample (or T(U)) closest to the DCP when compared to that far away from it. The in-between T(U)'s display a trend toward shrinkage in the renormalized Ising regime as T(U) shifts away from the DCP. Nevertheless, the crossover to the mean-field behavior is completed only beyond t>10(-2) for the T(U)'s studied. The observed crossover behavior is attributed to the presence of strong ion-induced clustering in this mixture, as revealed by various structure probing techniques, while the observed unique trend in the crossover behavior is discussed in terms of the varying influence of the DCP on the critical behavior along the T(U) line. The crossover behavior for the T(U)'s is pronounced and more sharp compared to the T(L)'s (lower critical solution temperatures) [U. K. Pradeep, J. Chem. Phys. 129, 134506 (2008)] in this mixture, although there exists no difference in the growth of the mesoscale clusters in the lower and upper one-phase regions in this mixture. Our observations suggest the need to look at the crossover behavior probably from two perspectives, namely, the dielectric effect and the clustering effect. The effective susceptibility exponent as a function of the field variable t(UL), instead of the conventional variable t, displays a sharp nonmonotonic crossover from its asymptotic 3D-Ising value ( approximately 1.24) toward a value slightly lower than its nonasymptotic mean-field value of 1, as that observed in the t analysis for the T(U) far away from the influence of the DCP.

Coexistence of liquid phases in the sodium polyphosphate-chromium nitrate-water system

The formation of coexisting liquid phases out of aqueous aluminum polyphosphate solutions was previously suggested as an essential step in aluminum polyphosphate nanoparticle formation. This hypothesis could not be directly verified because the separation of the two phases is very difficult, but a different situation was found in the case of chromium (III) polyphosphate. The phase diagram of the sodium polyphosphate-chromium nitrate-water system at 25 degrees C presents an extensive region with two coexisting liquid phases (L-L), together with a single liquid phase (L) and a solid-liquid (S-L) domain. Within the L-L region, admixture of the reagents produces initially a turbid liquid, out of which two transparent liquid phases separate in a short time, under gravity: one is dense, dark, and viscous while the other has a light color and a lower density. The amounts of the separated phases were determined, as well as their viscosities, densities, pH, UV-vis spectra, and relevant molalities: P (from polyphosphate), Cr(3+), NO(-)(3+), and Na(+). The two liquid phases undergo significant color, pH, and viscosity changes with time. The calculated phase diagrams display the major features of the experimental phase diagram.

Extraction of testosterone and epitestosterone in human urine using aqueous two-phase systems of ionic liquid and salt

Based on aqueous two-phase systems (ATPS) consisting of 1-butyl-3-methylimidazolium chloride, a hydrophilic ionic liquid (IL), and K2HPO4, a new and simple extraction technique, coupled with a reversed-phase high performance liquid chromatography (RP-HPLC), was developed for the simultaneous concentration and analysis of testosterone (T) and epitestosterone (ET) in human urine. Under the optimal conditions, the extraction efficiencies for both analytes were 80-90% in a one-step extraction. The method required only 3.0 mL of urine and a single hydrolysis/deproteinization/extraction step followed by direct injection of the IL-rich upper phase into HPLC system for analysis. The method has been satisfactorily applied to the analysis of T and ET in human urine with detection limits of 1 ng/mL and linear ranges of 10-500 ng/mL for both compounds. Compared with conventional liquid-liquid extraction or solid phase extraction, this new method is much "greener" due to no use of volatile organic solvent and low consumption of IL. The proposed extraction technique opens up new possibilities in the separation of other drugs.

Chromatographic and spectroscopic methods for the determination of solvent properties of room temperature ionic liquids

Room temperature ionic liquids are novel solvents with favorable environmental and technical features. Synthetic routes to over 200 room temperature ionic liquids are known but for most ionic liquids physicochemical data are generally lacking or incomplete. Chromatographic and spectroscopic methods afford suitable tools for the study of solvation properties under conditions that approximate infinite dilution. Gas-liquid chromatography is suitable for the determination of gas-liquid partition coefficients and activity coefficients as well as thermodynamic constants derived from either of these parameters and their variation with temperature. The solvation parameter model can be used to define the contribution from individual intermolecular interactions to the gas-liquid partition coefficient. Application of chemometric procedures to a large database of system constants for ionic liquids indicates their unique solvent properties: low cohesion for ionic liquids with weakly associated ions compared with non-ionic liquids of similar polarity; greater hydrogen-bond basicity than typical polar non-ionic solvents; and a range of dipolarity/polarizability that encompasses the same range as occupied by the most polar non-ionic liquids. These properties can be crudely related to ion structures but further work is required to develop a comprehensive approach for the design of ionic liquids for specific applications. Data for liquid-liquid partition coefficients is scarce by comparison with gas-liquid partition coefficients. Preliminary studies indicate the possibility of using the solvation parameter model for interpretation of liquid-liquid partition coefficients determined by shake-flask procedures as well as the feasibility of using liquid-liquid chromatography for the convenient and rapid determination of liquid-liquid partition coefficients. Spectroscopic measurements of solvatochromic and fluorescent probe molecules in room temperature ionic liquids provide insights into solvent intermolecular interactions although interpretation of the different and generally uncorrelated "polarity" scales is sometimes ambiguous. All evidence points to the ionic liquids as a unique class of polar solvents suitable for technical development. In terms of designer solvents, however, further work is needed to fill the gaps in our knowledge of the relationship between ion structures and physicochemical properties.

Controlling the aqueous miscibility of ionic liquids: aqueous biphasic systems of water-miscible ionic liquids and water-structuring salts for recycle, metathesis, and separations

Hydrophilic ionic liquids can be salted-out and concentrated from aqueous solution upon addition of kosmotropic salts forming aqueous biphasic systems as illustrated by the phase behavior of mixtures of 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) and K3PO4.