•Liquid-liquid equilibrium of binary {2-propanol + RTIL} solution was measured.•The critical exponents were deduced and found to belong to 3D-Ising universality.•Asymmetry of the coexistence curve was analyzed by the complete scaling theory.•The dependences of critical parameters on the permittivity of alkanols were discussed.The liquid-liquid coexistence curve and the heat capacity for binary solution of {2-propanol + 1-octyl-3-methylimidazolium hexafluorophosphate} have been precisely measured. The values of the critical exponents α and β, characterizing the critical anomalies of the heat capacity and the coexistence curve respectively, were deduced and found to be consistent with theoretical predictions. The asymmetric behavior of the diameter of the coexistence curve was studied in the frame of the complete scaling theory, demonstrating that the heat capacity related term is of importance. Furthermore, the restricted primitive model (RPM) was used to calculate the reduced upper consolute temperature and density, which together with a comparative larger value of A+ indicated a character of solvophobic criticality.

•Critical micelle concentrations and the degree of dissociations of counterion were determined.•The thermodynamic properties of micellization were calculated.•The compositions and excess properties in mixed micelles were evaluated.The mixed surfactants of dodecyltrimethylammonium bromide (DTAB) and 1-dodecyl-3-methylimidazolium bromide (C12mimBr) in aqueous solutions were studied by measurement of electrical conductivity and isothermal titration microcalorimetry (ITC). The critical micelle concentrations (cmc) and the degree of dissociations of counter ions were determined for this system at various surfactant compositions, and the thermodynamic properties of micellization were evaluated. A one-parameter Margules equation was used to fit the cmc values to calculate the mole fraction, the activity coefficients of two surfactant components and the excess properties in mixed micelles.

The densities of aqueous solutions of mixed surfactants of dodecyltrimethylammonium bromide and 1-dodecyl-3-methylimidazolium bromide (DTAB/C12mimBr) were measured at various compositions. The concentration dependent apparent molar volumes of these mixed surfactants were calculated and used to deduce the critical micelle concentrations (cmc) and the apparent molar volumes in the micelles and the continuous phase. The one-parameter Margules equation was applied to correlate the composition dependent cmc values and to obtain the activity coefficients and mole fractions of these surfactants in the mixed micelles, which were further used to calculate the excess Gibbs energies and the excess volumes. It was found that the excess Gibbs energies and the excess volumes of the mixed micelles are all negative, indicating that these mixed micelles are more stable and packed more tightly than their corresponding pure micelles.

The heats of mixing for a series of DTAB/TX100 mixed surfactant aqueous solutions were measured by flow-mixing calorimetry and isothermal titration calorimetry (ITC) at 298.15 K and 85 kPa, which were used to calculate the inter-micellar interaction enthalpies (−ΔHC). The signs of −ΔHC for pure DTAB and TX100 micellar systems were contrary to the inter-micellar interaction parameters reported for the same systems in the literature, suggesting that these interaction parameters might have a Gibbs free energy character dominated by entropy changes. It was found that the inter-micellar interaction enthalpies varied with the total surfactant concentration and the mixed ratio of the two surfactants, and characterized different structures of the mixed micelles. These phenomena were discussed based on the effects of structural water around the micellar interface, the hydration of counterions, and the repulsive Coulombic interaction.

•Liquid-liquid equilibrium of binary {ethanol + [C4mim][PF6]} solution was measured.•The critical exponents were deduced and found to belong to 3D-Ising universality.•Asymmetry of the coexistence curve was analyzed by the complete scaling theory.•Critical crossover from 3D-Ising to mean field behavior was discussed.The liquid-liquid coexistence curves in a temperature range of about 10 K from the upper consolute point and the specific isobaric heat capacities in a wide temperature range for the critical binary solution of {ethanol + 1-butyl-3-methylimidazolium hexafluorophosphate} have been reported. The critical exponents corresponding to the heat capacity and the coexistence curve were deduced and found to be consistent with theoretical predictions. The complete scaling theory was used to analyze the asymmetric behavior of the diameter of the coexistence curve, which confirmed that the heat capacity related term was of importance. The crossover behavior from the 3D-Ising to the mean field was examined and shown to be monotonic and more pronounced than that of simple fluids. It was also found that the system-dependent critical amplitude A+ for the heat capacity had a comparative large value, and the reduced critical parameters calculated from the restricted primitive model (RPM) were significantly larger than the characteristic RPM values, indicating the nature of solvophobic criticality.

Mixtures of polyoxyethylene tert-octyl phenyl ether (TX100) and dodecyltrimethylammonium bromide (DTAB) were investigated using isothermal titration calorimetry. On the base of the pseudophase separation model and using the two-parameter Margules equation, the compositions of mixed micelles and activity coefficient of each surfactant in mixed micelles were obtained and further used to calculate the thermodynamic parameters of micellization and excess properties of mixed surfactants in the micelles. Through three titration methods, the tendency of surfactants to form mixed micelles and the interactions between TX100 and DTAB in the micelles were investigated.

•(Liquid + liquid) equilibria of binary RTIL/alcohol solutions were measured.•Critical exponent was found to belong to 3D-Ising universality.•Asymmetry of the coexistence curves was analyzed.•RPM-rescaled critical parameters were calculated.•The dependences of critical parameters on the permittivity of alcohol were discussed.Precise (liquid + liquid) coexistence curves of binary mixtures {1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4]) + tert-butanol or RS-1,2-butanediol} have been measured. Critical exponent β   and critical amplitude B̂0Z were deduced from the (liquid + liquid) equilibria data in the critical regions, and it was found that the critical exponent β coincided well with the 3D-Ising value. The complete scaling theory was applied to describe the asymmetry behavior of the diameter of the coexistence curves, which suggested that the heat capacity related term showed significant importance. The reduced critical temperature and density were calculated by the restricted primitive model (RPM), which were used to discuss the driven force of phase separation. Moreover, the dependences of the critical temperature, the critical mole fraction, the reduced critical temperature and the reduced critical density on the permittivity of alcohol for a series of binary solutions of RTIL in alcohols are discussed.

The concentration-dependent enthalpies of mixing for water/sodium bis(2-ethylhexyl)-sulfosuccinate (AOT)/n-alkane microemulsions with different water contents ω0 and chain lengths n of n-alkane were determined by isothermal titration microcalorimetry (ITC) and flow-mixing microcalorimetry at 298.15 K and used to calculate the interaction enthalpies (−ΔHC) between the droplets. It was found that −ΔHC increased with ω0, and changed from negative to positive at about ω0 = 10. The investigation of the dependence of −ΔHC on n revealed that the values of −ΔHC were negative and had a minimum for ω0 = 5; while they were positive and had a maximum for ω0 = 15. These phenomena were discussed based on the competition of the overlapping contribution of the surfactant tails between two neighbouring droplets and the penetration contribution of the solvent molecules into the surfactant tails. These results indicated the important role of entropy in the stability of the microemulsion systems.

•Liquid–liquid equilibria of binary RTIL/alcohol solutions were measured.•Critical exponent was found to belong to 3D-Ising universality.•Asymmetry of the coexistence curves were analyzed.•RPM-rescaled critical parameters were calculated.Liquid–liquid phase equilibria of binary solutions of the room temperature ionic liquid (RTIL) 1-methyl-3-octylimidazolium tetrafluoroborate ([C8mim][BF4]) with 1-heptanol or 2-pentanol were measured. The critical exponents β obtained from the liquid–liquid equilibrium data in the critical region were consistent with the 3D-Ising value, which confirmed the 3D-Ising criticality of the investigated binary ionic solutions. The asymmetry of the diameters of the coexistence curves was analyzed by the complete scaling theory, indicating a significant contribution of the heat capacity related term. The RPM (restricted primitive model)-rescaled critical parameters were calculated, which showed dual characters of both solvophobic and coulombic criticalities of the studied binary ionic solutions.

•CMCs of mixed micelle systems of AOT/Dynol-604 were measured.•Dilution enthalpies of monomer and micelle in aqueous solutions were determined.•Micropolarity, sizes and aggregation numbers of the mixed micelles were measured.•Excess thermodynamic properties of the surfactant mixtures were reported.•Various interactions were discussed.Thermodynamic and microscopic properties of bis(2-ethylhexyl) sodium sulfosuccinate (AOT)/ethoxylated-2,5,8,11-tetramethyl-6-dodecyne-5,8-diol (Dynol-604) mixed micelles were investigated at 298.15 K by isothermal titration calorimetry, fluorimetry, and dynamic light scattering. Critical micellar concentrations, enthalpy changes upon dilution and micellization, the polarities of the microenvironment, the sizes and aggregation numbers of the micelles, and the excess thermodynamic quantities of the mixed micelles were obtained to deepen the understanding of the synergistic effect in the mixed surfactant systems.

Rates of SN1 hydrolysis reactions for 2-chloro-2-methylbutane in the critical solution of isobutyric acid + water and for 2-bromo-2-methylpropane in the critical solution of triethylamine + water in the one-phase region and at various temperatures have been determined respectively by conductance measurements. It was found that the reaction rates at different temperatures for those two SN1 reactions were well described by the Arrhenius equation in the noncritical region, whereas near the critical points the critical slowing down was clearly detected. These results are inconsistent with a previous report in the literature ( J. Phys. Chem. A 2003, 107, 8435−8443). Reanalyzing the literature data, we found that if an Arrhenius equation appropriate to either the one-phase region or the two-phase region being examined was used as the background, a critical slowing down rather than a speeding up was detected for the reaction in both the one-phase region and the two-phase region. The experimental data from different sources were fitted with a simplified crossover formalism characterizing the critical effect on the reactions to determine the critical slowing down exponents, which were found to be about 0.04, showing that only a dynamic critical slowing down could be detected for these reaction systems. This phenomenon was attributed to the fact that the SN1 hydrolysis reaction is neither a first-order nor a pseudo-first-order reaction in the reverse direction and the kinetic measurements were carried out in a region quite far from the equilibrium of the reactions.

Coexistences curves of liquid–liquid phase transition were reported for the binary solutions of the room temperature ionic liquid (RTIL) 1-octyl-3-methylimidazolium hexafluorophosphate ([C8mim][PF6]) with 1-propanol or tert-butanol. The critical amplitude B and the critical exponent β corresponding to the coexistence curve were deduced and the values of β were found to be consistent with the 3D-Ising value. Asymmetry of the diameters for the coexistence curves were examined and discussed in the frame of the complete scaling theory.

An isothermal titration calorimeter was used to measure the excess molar enthalpies (HE) at T = 298.15 K for five binary systems: 1-methyl-3-octyl-imidazolium tetrafluoroborate (OmimBF4) + alcohols (ethanol, 1-propanol, 2-propanol, 1-butanol, and 1-pentanol). The values of HE were found to be all positive for the five systems and were fitted with the Redlich–Kister polynomial and the UNIQUAC mode. The magnitude order of HE for the five systems was explained by the balance between the magnitude orders of enthalpies of the alcohol/alcohol and the alcohol/OmimBF4 interactions.

The densities of AOT/isooctane micelles and water/AOT/isooctane microemulsions with the molar ratios R of water to AOT being 2, 8, 10, 12, 16, 18, 20, 25, 30, and 40 were measured at 303.15 K. The apparent specific volumes of AOT and the quasi-component water/AOT at various concentrations were calculated and used to estimate the volumetric properties of AOT and water in the droplets and in the continuous oil phase, to discuss the interaction between the droplets, and to determine the critical micelle concentration and the critical microemulsion concentrations. A thermodynamic model was proposed to analysis the stability boundary of the microemulsion droplets, which confirms the maximum value of R being about 65 for the stable AOT/water/isooctane microemulsion droplets.

In this work, we studied the kinetics of the oxidation of iodide ion by persulfate ion in the critical water/bis(2-ethylhexyl) sodium sulfosuccinate (AOT)/n-decane microemulsions with the molar ratios of water to AOT being 35.0 and 40.8 via the microcalorimetry at various temperatures. It was found that the Arrhenius equation was valid for correlating experimental measurements in the noncritical region, but the slowing down effect existed significantly in the near critical region. We determined the values of the critical slowing down exponent and found it to be 0.187 ± 0.023 and 0.193 ± 0.032, respectively, which agreed well with the theoretical value of 0.207 predicted by the Griffiths–Wheeler rule for the singularity of the dimer/monomer droplet equilibrium in the critical AOT/water/n-decane microemulsions.

Mixed surfactant solutions are studied to understand their synergistic effects. Here we report the micellization properties of mixed surfactant solutions of the gemini surfactant N,N′-bis(dimethyldodecyl)-1,2-ethanediammoniumdibromide (12–2–12) with the imidazolium ionic liquid 1-dodecyl-3-methylimidazolium bromide (C12mimBr) investigated by isothermal titration calorimetry (ITC), conductometry, fluorimetry, and dynamic light scattering (DLS). A two-parameter Margules model was successfully used to correlate the cmc values and calculate the compositions and activity coefficients of the two components in the mixed micelle phase for 12–2–12/C12mimBr aqueous solutions with different overall surfactant compositions. The dissociation degree of counterion, the thermodynamic quantities of micellization, and the excess thermodynamic quantities for the mixed micelle were calculated and discussed. The ITC experiment in the low overall surfactant composition region showed a second phase transition. A thermodynamic model was proposed to explore phase behaviors of two different types of micelle and their solution, which was further confirmed by fluorescence and DLS studies.

•Coexistence curves of binary nitrobenzene/branched alkane solutions were measured.•Landau–Ginsburg–Wilson type model was tested.•Asymmetry of the coexistence curves was analyzed.•Heat capacity contribution to the diameter asymmetry was found to be important.The liquid–liquid coexistence curves for {x nitrobenzene + (1 − x) 2-methylpentane} and {x nitrobenzene + (1 − x) isooctane} were measured and the critical exponents and the critical amplitudes are deduced. The critical exponents were found to be consistent with the 3D-Ising value. The experiment results are analyzed to examine the dependences of the width and the asymmetry of the coexistence curves on the molar volume of the branched alkane. These dependences were also discussed through the Landau–Ginsburg–Wilson type model and the complete scaling theory.

Values of the enthalpy of dilution were measured for l-prolinol in pure water and N,N-dimethylformamide (DMF) aqueous solutions with various mass fractions of DMF at T = 298.15 K using a flow-mixing microcalorimeter. A pseudo phase equilibrium model was proposed to simplify the complex aggregation equilibrium and interpret the abnormality in the dilution enthalpy, which together with the McMillan–Mayer approach was used to fit the experimental data to obtain the enthalpic pairwise interaction coefficients and the molar aggregation enthalpies of l-prolinol in DMF aqueous solutions. The results are discussed in terms of the hydrophobic interaction and the interactions between the solvated solutes.Graphical abstractHighlights► The enthalpies of dilution were measured for l-prolinol in pure water and N,N-dimethylformamide aqueous solutions at 298.15 K. ► A pseudo phase equilibrium model is proposed and used to interpret the experimental results. ► The enthalpic pairwise interaction coefficients and the molar aggregation enthalpies are determined. ► The results are discussed in terms of the hydrophobic interaction and the interactions between the solvated solutes.

Turbidity in the one-phase region and the isobaric heat capacity per unit volume in both one-phase and two-phase regions for the critical solutions of {benzonitrile + n-alkane} were measured, from which the values of the system-dependent critical amplitudes for the correlation length, the osmotic compressibility, the heat capacity and the correction-to-scaling term of the heat capacity were deduced. The previously reported data of the coexistence curves for {benzonitrile + n-alkane} were also reanalyzed with the crossover model to obtain the crossover parameters. Subsequently, these results together with the values of the critical amplitude related to the coexistence curve reported previously were used to calculate some universal critical amplitude ratios, which showed reasonable agreement with the theoretical predictions.Highlights► Isobaric heat capacity and turbidity measurements have been reported. ► The coexistence curves have been reanalyzed by the crossover theory. ► Theoretical predictions of the universal amplitude ratios have been tested.

The interactions between sodium polyacrylate (PANa) and mixed micelles of dodecyltrimethylammonium bromide (DTAB) and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) were studied by isothermal titration calorimetry (ITC), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that the interaction mechanism varies with the titration order. For titration of PANa/AOT by DTAB, DTAB monomers first participate in the formation of AOT/DTAB mixed micelles, then bind to polymer individually, and subsequently result in the polymer-induced micellization characterized by two endothermic peaks. Only one endothermic peak was observed for titration of PANa by AOT/DTAB mixed micelle, corresponding to binding of the mixed micelles to the polymer. Exothermic peaks were observed for both types of titration characterizing the cross-link of the polymer chains. These interaction mechanisms were also interpreted by a thermodynamic model and confirmed by the measurements of SEM and TEM.

The kinetics of alkaline fading of crystal violet (CV) has been studied by UV spectrophotometry and microcalorimetry in the critical binary solution of 2-butoxyethanol + water at the initial reaction stage and various temperatures. It was found that the first-order rate constants obtained from these two methods are well accorded with each other, and the temperature dependence of the rate constant obeyed the Arrhenius equation in a temperature region far from the critical point. The critical slowing down was detected by both methods near the critical point. A simple empirical crossover model was proposed and used to analyze the experimental data to obtain the critical exponents, which were 0.158 ± 0.013 and 0.133 ± 0.012 from UV spectrophotometry and microcalorimetry, respectively, and the former was in good agreement with the theoretical prediction of 0.151. The slight lower value derived from microcalorimetry was attributed to the stirring in the microcalorimeter, which weakened the critical reduction of the diffusion coefficient.

The two Gemini surfactants (1-Dodecanaminium,N,N′-[[(2E)-1,4-dioxo-2-butene-1,4-diyl]bis(oxy-2,1-ethanediyl)]bis[N,N-dimethyl-,bromide)(12-fo-12) and (1-dodecanaminium,N,N′-[(1,4-dioxo-1,4-butanediyl)bis(oxy-2,1-ethanediyl)] bis[N,N-dimethyl-, bromide) (12-su-12), which have very similar structure but bearing rigid and flexible spacers respectively, and their monomeric counterpart 1-dodecanaminium, N-[2-(acetyloxy)ethyl]-N,N-dimethyl-, bromide (DTAAB) were synthesized and their aggregation behaviors in aqueous solutions were studied by measurements of the density and fluorescence. From the density measurements, the vesicle formation of 12-fo-12 was confirmed and the volumetric properties of the aggregates were obtained. By using fluorescence methods, the micropolarity, the steady-state anisotropy and the aggregation number in the micelles were measured. It was found that the rigidity of the spacer affected the microenvironmental properties significantly. The aggregation numbers were used to compare with those calculated from the geometric properties of the micelles by a simple geometry model, which showed good consistence with each other except for the calculations involving the surface area of the headgroup for the 12-su-12 system. It indicated that the surface area of 12-su-12 at the water–micelle interface was significantly larger than that at the water–air interface.Highlights► New volumetric method was proposed to detect the second aggregation point. ► The vesicle formation of the surfactant with rigid spacer was confirmed. ► The rigidity of the spacer affects the microenviromental properties greatly. ► Gemini surfactant has larger surface area at micelle interface than at water surface.

The kinetics of the alkaline hydrolysis of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in water/AOT/isooctane microemulsions has been studied by monitoring the absorbance change of the phenolphthalein in the system with time. The apparent first-order rate constant kobs has been obtained and found to be dependent on both the molar ratio of water to AOT ω and the temperature. The dependences of kobs on ω have been analyzed by a pseudophase model which gives the true rate constants ki of the AOT-hydrolysis reaction on the interface and the partition coefficients Kwi for the distribution of OH– between aqueous and interface pseudophases at various temperatures; the latter is almost independent of the temperature and ω. The temperature dependences of the reaction rate constants kobs and ki have been analyzed to obtain enthalpy ΔH≠, entropy ΔS≠, and energy Ea of activation, which indicate that the distribution of OH– between aqueous and interface pseudophases increases ΔS≠ but makes no contribution to Ea and ΔH≠. The influence of the overall concentration of AOT in the system on the rate constant has been examined and found to be negligible. It contradicts with what was reported by García-Río et al.(1) but confirms that the first-order reaction of the AOT-hydrolysis takes place on the surfactant interface. The study of the influence of AOT-hydrolysis on the kinetics of the alkaline fading of crystal violet or phenolphthalein in the water/AOT/isooctane microemulsions suggests that corrections for the AOT-hydrolysis in these reactions are required.

Liquid + liquid coexistence curves for the binary solutions of {benzonitrile + n-pentadecane} and {benzonitrile + n-heptadecane} have been measured in the critical region. The critical exponent β and the critical amplitudes have been deduced and the former is consistent with the theoretic prediction. It was found that the coexistence curves may be well described by the crossover model proposed by Gutkowski et al. The asymmetries of the diameters of the coexistence curves were also discussed in the frame of the complete scaling theory.Highlights► Coexistence curves of (benzonitrile + n-pentadecane) and (benzonitrile + n-heptadecane) were measured. ► The values of the critical exponent β are consistent with that predicted by the 3D-Ising model. ► The coexistence curves are well described by the critical crossover model. ► The asymmetry of the diameters of the coexistence curves were discussed by the complete scaling theory.

The liquid–liquid coexistence curves of (dimethyl adipate + n-octane) and (dimethyl adipate + n-nonane) have been determined within about 10 K from the critical temperatures, from which the critical amplitudes and the critical exponents are deduced. The critical exponents corresponding to the coexistence curve β are consistent with the 3D-Ising values. The experimental results have been analyzed to determine Wegner-correction terms and to discuss the asymmetric behaviour of the diameters of the coexistence curves by the complete scaling theory. Molar mass-dependences of the critical amplitude and the critical volume fraction have been shown to be consistent with the theoretical prediction.Highlights► Coexistence curves of (dimethyl adipate +n-octane or +n-nonane) were measured. ► The critical exponent β was found to be consistent with the 3D-Ising value. ► The asymmetry of the coexistence curves was discussed. ► The molar mass-dependence of the critical amplitude was investigated.

The liquid–liquid coexistence curves for (dimethyl adipate + n-hexane), (dimethyl adipate + n-heptane) have been measured, from which the critical amplitudes and the critical exponents are deduced. The critical exponent β corresponding to the coexistence curves are consistent with the 3D-Ising value. The experimental results have also been analyzed to determine the critical amplitudes of Wegner-correction terms when β and Δ are fixed at their theoretical values, and to examine the asymmetry of the diameters for the coexistence curves.Highlights► Coexistence curves of (dimethyl adipate + n-hexane) (+n-heptane) were measured. ► The critical exponent β are consistent with the 3D-Ising value. ► The asymmetry of the coexistence curves were discussed by complete scaling theory.

The enthalpies of dilution were measured for glycine betaine in water and in aqueous solutions of sodium chloride or potassium chloride at 298.15 K in a range of salt molality up to 1.2 mol·kg–1 using a flow–mixing microcalorimeter. The enthalpic interaction coefficients h2 and h3 were determined according to the McMillan–Mayer model and compared with that in glycine aqueous solutions. It was found that the enthalpic pairwise interaction coefficients h2 of GB in both brine solutions are positive and increase with the molality of the salts. The value of h2 in aqueous solutions of sodium chloride is larger than that in the aqueous solutions of potassium chloride with the same molality.

The reactions of the alkaline fading of phenolphthalein (PN) have been studied in water/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/isooctane microemulsions by monitoring the absorbance changes of PN in the system with the time and the results compared with those found for the same reactions in aqueous solutions. It was found that the values of the equilibrium constants and the forward reaction rate constants in the microemulsions were significantly larger than that in aqueous solutions and decreased with increasing the molar ratio of water to AOT (ω), except for that with low ω. The temperature dependence of the reaction rate constant was analyzed to obtain the values of free energy, enthalpy, and entropy of activation, which suggests the existence of an isokinetic relationship and a common mechanism for the reactions occurring in the microemulsions with different ω. It was also observed that the competition between the reactions of the alkaline fading of PN and the hydrolyzation of AOT in water/AOT/isooctane microemulsions when the reaction time was sufficiently long.

(Liquid + liquid) coexistence curve, turbidity, and isobaric heat capacity per unit volume for the critical solution of {benzonitrile + n-tetradecane} have been measured. The critical exponents β, ν, γ, and α and system-dependent critical amplitudes B, ξ0, χ0, and A±, corresponding to the difference of the general density variable of two coexisting phases Δρ, the correlation length ξ, the osmotic compressibility χ, and the isobaric heat capacity per unit volume CpV−1, have been deduced and were used to test some universal ratios. The behavior of the diameter of the coexistence curves showed good agreement with the complete scaling theory. The analysis of effective critical exponent βeff, which was well described by the crossover model proposed by Anisimov and Sengers, and effective critical exponent αeff indicated monotonic crossover phenomena from 3D-Ising behavior to mean-field one as the temperature departed from the critical point.Research highlights► Coexistence curve, turbidity and heat capacity of critical solution were measured. ► Critical amplitudes were determined to test universal ratios. ► Complete scaling theory was verified. ► Monotonic critical crossover behavior was demonstrated.

Densities and isobaric heat capacities per unit volume have been measured for binary mixtures {x benzonitrile + (1 − x) octane} and {x benzonitrile + (1 − x) nonane} in the temperature ranges of (283.15 to 318.15) K and (283.15 to 313.15) K, respectively. Measurements covered the whole composition range at the ambient pressure. From these measured data, the excess molar volumes, excess isobaric thermal expansivities, and excess isobaric molar heat capacities were calculated and fitted with the Redlich−Kister equation. The excess molar volumes, excess isobaric thermal expansivities, and excess isobaric molar heat capacities of both systems were found to exhibit the S-shaped curves against the composition and the feature of the nonrandomness mixing. The dependences of these properties on the temperature and composition were analyzed and discussed in terms of the natures of the two pure components and the molecular interactions in the mixtures.

Liquid + liquid coexistence, light scattering, and isobaric heat capacity per unit volume for the critical solutions of (benzonitrile + n-nonane) have been measured. The critical exponents relating to the coexistence curve β, the osmotic compressibility γ, the correlation length ν, and the heat capacity α have been deduced and the values are consistent with the 3D-Ising values in the range close to the critical point. The experimental results of the liquid + liquid coexistence were analyzed to examine the Wegner correction terms and the behaviour of the diameter of the coexistence curves. The light scattering data were well described by the crossover model proposed by Anisimov and Sengers, and showed a tendency of monotonic crossover of the critical exponents γ and ν from the 3D-Ising values to the mean-field values as the temperature departures from the critical point. From calorimetric measurements, the amplitude A± and the critical background Bcr of the heat capacity in the critical region have been deduced and some universal ratios are tested.

The interactions between the anionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT) and the polycation poly(diallydimethylammonium chloride) (PDDAC), the aggregations of AOT and PDDAC-bound AOT in PDDAC/AOT aqueous solutions, and the influence of salt on the interactions and aggregations have been studied by isothermal titration calorimetry (ITC), dynamic light scattering (DLS), and negative staining transmission electron microscopy (TEM). The adsorptions of AOT onto PDDAC and the formations of PDDAC-bound AOT micelles, free AOT micelles, and AOT vesicles were examined, and the corresponding critical concentrations were determined. Combining calculations of thermodynamic parameters with the above three experimental techniques, it was shown that the micellization of free AOT is driven by entropy gain, while the adsorption of AOT onto PDDAC and the micellization of PDDAC-bound AOT are driven by both enthalpy and entropy. It was also found that addition of salt enhances the binding of AOT onto PDDAC through the ion exchange and favors the formations of PDDAC/AOT micelles, free AOT micelles, and free AOT vesicles but prevents the transition of PDDAC/AOT micelles to the vesicles. Thermodynamic analysis suggested that the adsorption of AOT onto PDDAC and the micellization of PDDAC/AOT in PDDAC/AOT brine solutions are different in mechanism compared with that in corresponding aqueous solutions.

The coexistence curves and light scattering data for a critical solution of (benzonitrile + dodecane) have been reported. The critical exponents relating to the difference in density variables of two coexisting phases β, the correlation length ν, and the osmotic compressibility γ have been determined. The experimental results of the coexistence curves have also been analyzed to examine the Wegner correction terms and the behavior of the diameter of the coexistence curves. The data analysis shows that the 3D-Ising behavior is valid in a temperature range close to the critical point. However, in a wide temperature range the exponential values of ν and γ change with the temperature significantly, clearly exhibiting the critical crossover from the 3D-Ising universality class to the classical one.

The coexistence curves and light scattering data for a critical solution of benzonitrile + octadecane have been reported. The critical exponents relating to the difference in density variables of two coexisting phases β, the correlation length ν, and the osmotic compressibility γ have been calculated. The experimental results of the coexistence curves have also been analyzed to examine the Wegner correction terms and the behavior of the diameter of the coexistence curves. The data analysis shows that the 3D-Ising behavior is valid in a temperature range close to the critical point. However in a wide temperature range the exponential values of ν and γ change with the temperature significantly, clearly exhibiting the critical crossover from the 3D-Ising universality class to the classical one.

The coexistence curves of {water + KCl + sodium di(2-ethyl-1-hexyl)sulphosuccinate (AOT) + decane} microemulsion system have been determined by measuring refractive index at constant pressure in the critical region. The critical exponent β has been deduced from coexistence curves. The values of β decrease with increase in the temperature range (T − Tc) and approach the Ising value in the region of 1 K above Tc. The experimental results have been analyzed to examine the Wegner correction terms and the behaviors of the diameters of the coexistence curves. It was found that addition of salt KCl into the ternary microemulsion of {water + AOT + decane} almost did not change the critical concentration but significantly raised the critical temperature. Addition of salt also significantly reduced the region of validity of simple scaling and the efficiency of the variable of volume fraction ϕ as an order parameter to describe the critical asymptotic behaviors.

The power-law dependences of critical amplitudes either on the molar volume of cycloalkane or on the interaction parameter per unit volume for coexistence curve, correlation length and susceptibility have been derived from a Landau–Ginsburg–Wilson model and the Scatchard–Hildebrand theory for solutions of cycloalkanes in a polar solvent. Coexistence curves of (T, n), (T, x) and (T, ϕ), where n, x, and ϕ are refractive index, mole fraction and volume fraction respectively, for the binary mixtures of methylcyclopentane and cycloheptane in N-methyl-2-pyrrolidone (NMP) have been determined in the critical regions by measurements of n. The critical amplitude B and the critical exponent β have been deduced. The experimental results reported in this work and previous work are in good agreement with theoretical predictions.

Coexistence curves of (T,n), (T,x) and (T,φ), where n, x, and φ are refractive index, mole fraction and volume fraction, respectively, for the binary mixtures {xN-methyl-2-pyrrolidone (NMP) + (1−x)cyclohexane} and {xNMP + (1−x)cyclooctane} have been determined in the critical regions by measurements of n. The critical amplitude B and the critical exponent β have been deduced and the values of β are consistent with the theoretical ones. The experimental results have been analysed to examine the Wegner correction terms and the behaviour of the rectilinear diameter of the coexistence curves. The coexistence curves have been successfully described by a combination of the Wegner equation and the expression for the diameter. The power law dependence of critical behaviour either on the molar volume of cycloalkane or on the interaction parameter per unit volume has also been discussed.

•Liquid–liquid equilibria of binary RTIL/alcohol solutions were measured.•Asymmetry of the coexistence curves was analyzed.•Critical behaviors of RTIL/alcohol solutions were investigated.•Dependences of critical parameters on the solvent's permittivity were studied.The liquid–liquid coexistence curves for the binary solutions of the room temperature ionic liquid (RTIL) 1-methyl-3-octylimidazolium tetrafluoroborate ([C8mim][BF4]) in 1-pentanol and 1-hexanol were measured in the critical region. The critical exponent β and the critical amplitude B were deduced and the former was found to be consistent with the 3D-Ising value. The complete scaling theory was applied to describe the asymmetry of the diameters of the coexistence curves. Moreover, the dependences of the critical temperature, the critical mole fraction, the reduced critical temperature and the reduced critical density on the permittivity of alcohol for a series of binary solutions of RTIL in alcohols were discussed.

•An approach was developed to obtain the intermicellar interaction enthalpy.•The aggregation number and the second virial coefficient were determined by light scattering.•The interaction enthalpy was found to be negative.•The nature of the inter-micellar interaction was clarified.In order to clarify the nature of the inter-micellar interactions, we developed an approach to obtain the intermicellar interaction enthalpy through measuring the mixing heats of dodecyltrimethylammonium bromide (DTAB)/1-dodecyl-3-methylimidazolium bromide (C12mimBr) mixed micelles by using flow-mixing calorimetry. It was found that the inter-micellar interaction enthalpies for this system were negative, representing the attractive enthalpy interactions between the mixed micelle droplets. These results are contradictory to those reported in the literature and interpreted by the predominant attractive dehydration effect of counterion. Static light scattering experiment revealed that the repulsive nature of the interaction characterized by the Gibss free energy should be dominated by the entropy interaction.Download high-res image (113KB)Download full-size image