Water-rich Mixtures Research Articles

Solubility, Solution Thermodynamics, and Preferential Solvation of Amygdalin in Ethanol + Water Solvent Mixtures.

The equilibrium solubility of amygdalin in [ethanol (1) + water (2)] mixtures at 293.15 K to 328.15 K was reported. The thermodynamic properties (standard enthalpy ΔsolnH°, standard entropy ΔsolnS°, and standard Gibbs energy of solution ΔsolnG°) were computed using the generated solubility data via van’t Hoff and Gibbs equations. The dissolution process of amygdalin is endothermic and the driving mechanism in all mixtures is entropy. Maximal solubility was achieved in 0.4 mole fraction of ethanol at 328.15 K and the minimal one in neat ethanol at 293.15 K. Van’t Hoff, Jouyban–Acree–van’t Hoff, and Buchowski–Ksiazczak models were used to simulate the obtained solubility data. The calculated solubilities deviate reasonably from experimental data. Preferential solvation parameters of amygdalin in mixture solvents were analyzed using the inverse Kirkwood–Buff integrals (IKBI) method. Amygdalin is preferentially solvated by water in ethanol-rich mixtures, whereas in water-rich mixtures, there is no clear evidence that determines which of water or ethanol solvents would be most likely to solvate the molecule.

Solubility of meloxicam in aqueous binary mixtures of formamide, N-methylformamide and N,N-dimethylformamide: Determination, correlation, thermodynamics and preferential solvation

In this research the experimental solubility of meloxicam (MLX) in {formamide (FM) + water}, {N-methylformamide (NMF) + water} and {N,N-dimethylformamide (DMF) + water} mixtures were determined at five temperatures, 293.15 K, 298.15 K, 303.15 K, 308.15 K and 313.15 K. MLX solubility increases with the cosolvent proportion in the mixtures and with temperature arising. Experimental solubility of MLX was modelled by using three well-known cosolvency models, namely the combined nearly ideal binary solvent/Redlich-Kister (CNIBS/R-K), Modified-Wilson model and Jouyban-Acree model. The mean relative deviation (MPD%), in the accuracy of each mathematical model in relation to experimental solubility, shown CNIBS/R-K model is better in contrast to the other models. The model results were below of 3.21% for (FM + water) mixtures, to each temperature in the study. Furthermore, these were below of 1.72% for (NMF + water) mixtures and below of 1.70% for (DMF + water) mixtures, respectively. Apparent thermodynamic quantities of dissolution and mixing, as well as the preferential solvation parameters of MLX were calculated. Gibbs energies and enthalpies of dissolution were positive whereas the respective entropies were negative. MLX is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by cosolvent molecules in mixtures of cosolvent-rich mixtures.

Solubility of meloxicam in (Carbitol® + water) mixtures: Determination, correlation, dissolution thermodynamics and preferential solvation

The equilibrium solubility of meloxicam (3) in {Carbitol® (1) + water (2)} mixtures at several temperatures from 293.15 K to 313.15 K has been determined and correlated by means of some well-known thermodynamic correlation models. Solubility increases 1144 times, from x3 = 1.137 × 10−6 in neat water to x3 = 1.300 × 10−3 in neat Carbitol® at 298.15 K. By using the van't Hoff and Gibbs equations the respective apparent thermodynamic quantities of the dissolution and mixing processes, namely Gibbs energy, enthalpy, and entropy, were calculated. Apparent dissolution enthalpies vary from a minimum of 7.7 kJ mol−1 in neat water to a maximum of 32.3 kJ mol−1 in the mixture x1 = 0.10. Moreover, apparent dissolution entropies vary from a minimum of −88.0 J mol−1 K−1 in neat water to a maximum of 9.9 J mol−1 K−1 in the mixture x1 = 0.10. Non-linear enthalpy–entropy relationship was observed for meloxicam in the plot of enthalpy vs. Gibbs energy exhibiting negative slope in the composition region 0.00 < x1 < 0.10 and variant but mainly positive slopes in the other mixtures. Hence, the driving mechanism for meloxicam transfer process from more polar to less polar solvent systems is the entropy in water-rich mixtures and the enthalpy in the other solvent compositions. Furthermore, the preferential solvation of meloxicam by Carbitol® and water was analysed by using the inverse Kirkwood-Buff integrals. Meloxicam is preferentially solvated by water molecules in water-rich mixtures exhibiting a maximum in the mixture x1 = 0.10 with δx1,3 = −3.19 × 10−2 but preferentially solvated by Carbitol® molecules in mixtures 0.12 < x1 < 1.00 exhibiting a maximum in the mixture x1 = 0.20 with δx1,3 = 6.87 × 10−2.

Dissolution thermodynamics and preferential solvation of meloxicam in (acetonitrile + water) mixtures

ABSTRACT Solubility of meloxicam in {acetonitrile + water} mixtures at five temperatures from 293.15 K to 313.15 K has been determined and correlated by means of the Jouyban-Acree model. By using the van’t Hoff and Gibbs equations the respective apparent thermodynamic quantities for the dissolution and mixing processes, namely Gibbs energy, enthalpy, and entropy, were calculated. Non-linear enthalpy–entropy relationship was observed in the plot of enthalpy vs. Gibbs energy exhibiting negative slope in the composition region 0.00 < x 1 < 0.20 and variant slopes in the other mixtures. Based on the inverse Kirkwood-Buff integrals it follows that meloxicam is preferentially solvated by water molecules in water-rich and acetonitrile-rich mixtures but preferentially solvated by acetonitrile molecules in mixtures 0.26 < x 1 < 0.60.

Preferential solvation of apremilast in some (Transcutol® + water) mixtures

Shakeel et al. reported the equilibrium solubility of apremilast (3) in some {transcutol (1) + water (2)} mixtures at several temperatures with some numerical correlation analysis. Nevertheless, no attempt was made to evaluate the preferential solvation of this compound by the solvents. In this communication the preferential solvation of apremilast in the saturated mixtures at 298.15 K was analyzed based on the inverse Kirkwood-Buff integrals as described in the literature. Apremilast is preferentially solvated by water in water-rich mixtures (0.00 < x1 < 0.12) but preferentially solvated by transcutol in mixtures with composition 0.12 < x1 < 1.00. These results could be interpreted as a consequence of hydrophobic hydration around the non-polar groups of the solute in the former case. Moreover, in the last case, the observed trend could be a consequence of the acid behavior of apremilast in front to transcutol molecules because this cosolvent is more basic than water as described by the respective solvatochromic parameters.

Dissolution thermodynamics and preferential solvation of gliclazide in (Transcutol® + water) mixtures

ABSTRACT The equilibrium solubility of gliclazide (3) in {Transcutol (1) + water (2)} mixtures at several temperatures was reported in the literature. However, no deep attempt was made to correlate gliclazide solubility with the composition of the aqueous-cosolvent mixtures. Moreover, no apparent thermodynamic calculations for the dissolution processes were performed. Thus, the reported solubility data were modelled by means of some well-known correlation models. By using the van’t Hoff and Gibbs equations, the respective apparent thermodynamic quantities of dissolution and mixing processes, namely Gibbs energy, enthalpy, and entropy, were calculated. Non-linear enthalpy–entropy relationship was observed for gliclazide in the plot of enthalpy vs Gibbs energy exhibiting negative slope in the composition region 0.00 < w 1 < 0.10 and variant but mainly positive slopes in the other mixtures. Hence, the driving mechanism for gliclazide transfer process from more polar to less polar solvent systems is the entropy in water-rich mixtures and the enthalpy in the other solvent compositions. Furthermore, the preferential solvation of gliclazide by both solvents was analysed by using the inverse Kirkwood-Buff integrals observing that gliclazide is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by Transcutol molecules in mixtures 0.12 < x 1 < 1.00.

Dissolution thermodynamics and preferential solvation of ketoconazole in some {ethanol (1) + water (2)} mixtures

In this research, the equilibrium mole fraction solubility of ketoconazole in some aqueous-ethanolic mixtures was calculated from previously measured solubility data reported in molarity scale at temperatures from 298.2 to 313.2 K. Experimental mole fraction solubility values were adequately correlated with the Jouyban-Acree and Jouyban-Acree-van't Hoff models. The respective apparent thermodynamic functions (Gibbs energy, enthalpy, and entropy of the dissolution processes) were computed using the van't Hoff and Gibbs equations. The enthalpy–entropy relationship for ketoconazole was non-linear in the plot of enthalpy vs. Gibbs energy of solution with negative slope in the composition region 0.00 ≤ w1 ≤ 0.20 but positive slope in the region 0.20 ≤ w1 ≤ 0.70. Beyond this composition, the behavior is more complex. Therefore, the driving mechanism for ketoconazole dissolution process is the entropy in water-rich mixtures and the enthalpy in mixtures 0.20 ≤ w1 ≤ 0.70. In addition, the inverse Kirkwood-Buff integrals were used to investigate the preferential solvation of ketoconazole which is preferentially solvated by water molecules in water-rich and also in ethanol-rich mixtures but preferentially solvated by ethanol molecules in mixtures 0.24 ≤ x1 ≤ 0.75. Dissolution thermodynamics and preferential solvation computations were carried out employing whole experimental solubility data points and the simulated data using a minimum number of seven data points as training set, in which there were no significant differences in the obtained numerical values except for enthalpy-entropy compensation data.

Preferential solvation of some corticosteroids in {ethanol (1) + water (2)} mixtures at 298.2 K

The equilibrium solubility of three corticosteroids, namely, budesonide, hydrocortisone and prednisolone in some {ethanol (1) + water (2)} mixtures as expressed in mole fraction at 298.2 K was calculated from reported solubility values expressed in molarity scale. Further, by using the inverse Kirkwood-Buff integrals is observed that these drugs are preferentially solvated by water molecules in water-rich mixtures and apparently also in ethanol-rich mixtures but preferentially solvated by ethanol molecules in mixtures of similar proportions of the solvents.

Further comments on “Experimental measurements, equilibrium study and model correlation of methyl paraben in ethanol and methanol aqueous solutions from = (293.15 to 323.15) K”

The experimental solubility data of methyl paraben in ethanol + water and methanol + water binary solvent mixtures at temperature range from (293.15 to 323.15) K have carefully been reanalyzed and some recommendations were proposed. In addition, preferential solvation analyses based on the inverse Kirkwood-Buff integrals show that this compound is preferentially solvated by water in water-rich mixtures in both binary systems but preferentially solvated by the cosolvent in the composition region of 0.24 < x1 < 1.00 for ethanol + water mixtures and the composition region of 0.31 < x1 < 1.0 for methanol + water mixtures.

Stability of Monoterpene-Derived α-Hydroxyalkyl-Hydroperoxides in Aqueous Organic Media: Relevance to the Fate of Hydroperoxides in Aerosol Particle Phases.

The α-hydroxyalkyl-hydroperoxides [R-(H)C(-OH)(-OOH), α-HH] produced in the ozonolysis of unsaturated organic compounds may contribute to secondary organic aerosol (SOA) aging. α-HHs' inherent instability, however, hampers their detection and a positive assessment of their actual role. Here we report, for the first time, the rates and products of the decomposition of the α-HHs generated in the ozonolysis of atmospherically important monoterpenes α-pinene (α-P), d-limonene (d-L), γ-terpinene (γ-Tn), and α-terpineol (α-Tp) in water/acetonitrile (W/AN) mixtures. We detect α-HHs and multifunctional decomposition products as chloride adducts by online electrospray ionization mass spectrometry. Experiments involving D2O and H218O, instead of H216O, and an OH-radical scavenger show that α-HHs decompose into gem-diols + H2O2 rather than free radicals. α-HHs decay mono- or biexponentially depending on molecular structure and solvent composition. e-Fold times, τ1/e, in water-rich solvent mixtures range from τ1/e = 15-45 min for monoterpene-derived α-HHs to τ1/e > 103 min for the α-Tp-derived α-HH. All τ1/e's dramatically increase in <20% (v/v) water. Decay rates of the α-Tp-derived α-HH in pure water increase at lower pH (2.3 ≤ pH ≤ 3.3). The hydroperoxides detected in day-old SOA samples may reflect their increased stability in water-poor media and/or the slow decomposition of α-HHs from functionalized terpenes.

Thermodynamic solubility, solvent effect and preferential solvation analysis of rebamipide in aqueous co-solvent mixtures of propylene glycol, n-propanol, isopropanol and ethanol

Mole fraction solubility of rebamipide (R- and S-enantiomer mixtures with a mole ratio of 50:50) in mixtures of propylene glycol (PG, 1) + water (2), n-propanol (1) + water (2) , isopropanol (1) + water (2) and ethanol (1) + water (2) was reported at temperature range from (273.15 to 318.15) K. All experiments were made by the use of the isothermal saturation technique under ambient pressure of 101.2 kPa. At the same mass fraction proportions of PG, n-propanol, isopropanol or ethanol and temperature, the rebamipide solubility was highest in the PG (1) + water (2) mixture. The solubility data were correlated mathematically through the Jouyban-Acree model, attaining RAD values lower than 6.35% and RMSD values lower than 6.73 × 10−6. Quantitative values for local mole fraction of PG (n-propanol, isopropanol or ethanol) and water adjacent the rebamipide were determined by means of the Inverse Kirkwood–Buff integrals method applied to the determined solubility data. The preferential solvation parameters were negative in the water-rich mixtures but positive in the co-solvent compositions from 0 to 0.20 in mole fraction of n-propanol/PG, and from 0 to 0.25 in mole fraction of ethanol/isopropanol, respectively. It was conjectured that the preference of rebamipide in water-rich mixtures could be the result from the higher basic behaviour of rebamipide molecules interacting with the proton-donor functional groups of the water. In addition, the solubility variation over the composition range was analysed by KAT-LSER model to distinguish the main factors that explained solvent effect on solubility of rebamipide in the PG (n-propanol, isopropanol or ethanol) + water mixtures. It was found that the rebamipide solubility variation was mainly due to the change in the hydrogen bond acidity and cavity term for the ethanol (isopropanol, n-propanol) mixtures and the cavity term for the PG + water mixture.

Measurement and modelling of the solubility for ketoconazole in {acetonitrile + water} mixtures at T = (293.2 to 313.2) K

ABSTRACT The solubilisation behaviour of ketoconazole in the binary mixtures of acetonitrile and water was studied at T = (293.2–313.2) K. The solubility data were represented with seven co-solvency models including Jouyban-Acree, Jouyban-Acree-van’t Hoff, NRTL, Wilson, UNIQUAC, combined nearly ideal binary solvent/Redlich-Kister and modified Wilson models. The computed thermodynamic properties of dissolution suggest that except in neat water, the main contributor to standard Gibbs free energies of dissolution is enthalpy. Furthermore, preferential solvation analysis shows that ketoconazole is preferentially solvated by water in water-rich mixtures and also in acetonitrile-rich mixtures but preferentially solvated by acetonitrile in mixtures of intermediate compositions.

Solubility of sulfacetamide in aqueous propylene glycol mixtures: Measurement, correlation, dissolution thermodynamics, preferential solvation and solute volumetric contribution at saturation

The equilibrium solubility at temperatures from (278.15 to 318.15) K, dissolution thermodynamics, preferential solvation, and apparent specific volume at saturation of sulfacetamide (SCM) in {propylene glycol (PG) (1) + water (2)} mixtures is reported. Mole fraction solubility of SCM (x3) increases when temperature arises and also increases with the PG proportion arising. Solubility behavior was adequately correlated and/or predicted by the Jouyban-Acree and Jouyban-Acree-van't Hoff models and the obtained mean percentage deviations (MPD) are varied between 6.5 and 11.5%. Apparent thermodynamic analysis of dissolution and mixing was performed in all the mixtures and neat solvents. Based on the inverse Kirkwood-Buff integrals (IKBI) is observed that SCM is preferentially solvated by water molecules in water-rich mixtures but preferentially solvated by PG in the other mixtures. Further, the apparent specific volumes of SCM at saturation were also calculated.

The solubility of ketoconazole in binary carbitol + water mixtures at T = (293.2–313.2) K

The solid-liquid equilibrium of ternary {ketoconazole + carbitol + water} systems was studied by a shake-flask technique at T = (293.2–313.2) K and atmospheric pressure. The temperature and solvent composition dependency models of Jouyban-Acree, Jouyban-Acree-van't Hoff, NRTL, UNIQUAC and Wilson as well as solvent composition dependency models of combined nearly ideal binary solvent/Redlich-Kister (CNIBS/R-K) and modified Wilson were utilized for modeling the experimental solubility data. To predict the solubility data, Yalkowsky and extended Yalkowsky models were utilized. It was observed that the solubility of ketoconazole was increased with the enhancement in temperature and concentration of carbitol. According to the % ARD values, order of performance of the models with temperature and solvent composition dependencies are Jouyban-Acree-van't Hoff > NRTL > Jouyban-Acree > UNIQUAC > Wilson. The % ARD values indicate that in comparison between the models with solvent composition dependency, CNIBS/R–K model has a better consistency with the experimental data. Further, the computed thermodynamic properties of dissolution for ketoconazole in aqueous carbitol solutions suggest that except in neat water, enthalpy has the main contribution to standard Gibbs free energies of dissolution. Finally, preferential solvation analysis based on the inverse Kirkwood-Buff integrals demonstrates that ketoconazole is preferentially solvated by water in water-rich mixtures but preferentially solvated by carbitol in mixtures of 0.12 < x1 < 1.00.

Ketoconazole solubility in aqueous binary mixtures of 1‑propanol at various temperatures

The aim of this work is to have a brief overview on various solubilization methods reported for ketoconazole and using a commonly used method, i.e. cosolvency for enhancement of ketoconazole in binary mixtures of 1‑propanol and water at different temperatures. The generated data are correlated with eight cosolvency mathematical models including the van't Hoff, the double log-log, the mixture response surface, Yalkowsky, Jouyban-Acree, Jouyban-Acree-van't Hoff, modified Jouyban-Acree-van't Hoff, and the modified Wilson models. The mean relative deviations (MRD%) of the back-calculated solubility for each investigated models are calculated as an accuracy criterion. Density of the ketoconazole saturated solutions as another physico-chemical properties is also fitted by the Jouyban-Acree model. Moreover, standard enthalpy, entropy and Gibbs free energy change for ketoconazole dissolution process were obtained by using van't Hoff and Gibbs equations. Finally, preferential solvation analysis based on the inverse Kirkwood-Buff integrals demonstrates that ketoconazole is preferentially solvated by water in water-rich mixtures but preferentially solvated by 1‑propanol in mixtures of 0.19 < x1 < 1.00.

Measurement and mathematical modeling of ketoconazole solubility in propylene glycol + water mixtures at various temperatures

The aim of this work was to study the solubilization behavior and thermodynamics of ketoconazole solubility in the binary mixtures of propylene glycol (PG) and water at five different temperatures ranging T = 293.2–313.2 K. Some cosolvency mathematical models including van't Hoff equation, Yalkowsky model, Jouyban-Acree model, Jouyban-Acree-van't Hoff model, modified Jouyban-Acree-van't Hoff model, the modified Wilson model, the double log-log model and the mixture response surface model were fitted to the experimental results, and the mean relative deviations (MRD%) of the back-calculated solubilities were calculated. Density of the solutions saturated with ketoconazole over the entire solvent composition and temperature range was also determined and the obtained density values were correlated/back-calculated with the Jouyban–Acree model, resulting in a very accurate calculation of the densities with MRD% of 0.1%. Moreover, apparent thermodynamic properties of ketoconazole dissolution process in the investigated mixed solvents including entropy, enthalpy and Gibbs free energy were computed using van't Hoff and Gibbs equations. Furthermore, preferential solvation analysis demonstrates that ketoconazole is preferentially solvated by water in water-rich mixtures but preferentially solvated by PG in the other mixtures.

Solvent effect on solubility and preferential solvation analysis of buprofezin dissolved in aqueous co-solvent mixtures of N,N-dimethylformamide, ethanol, acetonitrile and isopropanol

The mole fraction solubility of buprofezin in aqueous co-solvent mixtures of N,N-dimethylformamide (DMF,1) + water (2), ethanol (1) + water (2), isopropanol (1) + water (2) and acetonitrile (1) + water (2) over the temperature range from (273.15 to 318.15) K was reported. At the same composition of DMF, ethanol, isopropanol or acetonitrile and temperature, the buprofezin solubility was highest in DMF (1) + water (2) mixtures. By using the Jouyban-Acree model, the buprofezin solubility was correlated obtaining RAD lower than 5.86% and RMSD lower than 15.60 × 10−4. Quantitative values for local mole fraction of DMF (ethanol, isopropanol or acetonitrile) and water nearby the buprofezin were calculated through the Inverse Kirkwood–Buff integrals method applied to the solubility. The values of preferential solvation parameters (δx1,3) were negative in water-rich mixtures but positive in co-solvent compositions from 0.19, 0.20 (0.25) or 0.25 to 1 in mole fraction of DMF, isopropanol, ethanol or acetonitrile, respectively. It was conjecturable that in water-rich mixtures, the hydrophobic hydration around the nonpolar methyl groups and aromatic ring group of buprofezin played a relevant important role in the solvation. The preference of buprofezin in water-rich mixtures could be explained in terms of the higher basic behaviour of buprofezin molecules interacting with the proton-donor functional groups of the water. In addition, solute-solvent and solvent-solvent interactions of buprofezin in the DMF (ethanol, isopropanol or acetonitrile) + water mixtures were investigated from the solubility data by using the linear solvation energy relationships concept. The variation of buprofezin solubility depended mainly upon the hydrogen bond acidity and cavity term for ethanol (isopropanol) + water mixtures, and the cavity term for DMF (acetonitrile) + water mixtures.

Solubility of sulfacetamide in (ethanol + water) mixtures: Measurement, correlation, thermodynamics, preferential solvation and volumetric contribution at saturation

The equilibrium solubility at temperatures from (278.15 to 313.15) K, dissolution thermodynamics, preferential solvation, and apparent specific volume at saturation of sulfacetamide (SCM) in {ethanol (1) + water (2)} mixtures is reported. Mole fraction solubility of SCM (x3) increases when temperature arises and also increases with the ethanol proportion increasing reaching maximum values in the mixture w1 = 0.80. It varies from 7.06 × 10−4 in neat water to 2.506 × 10−2 in the mixture w1 = 0.80 at 298.15 K. Solubility behavior was adequately correlated by various cosolvency models and the obtained mean percentage deviations (MPD) varied between 2.6 and 15.9%. Moreover, the trained Jouyban-Acree model using a minimum number of 7 data points is used for predicting the rest of data points with the MPD of ~14% (N = 81). In addition, the generally trained model (Jouyban-Acree-Abraham) was also used to predict the solubility data of SCM in {ethanol (1) + water (2)} mixtures and obtained MPD for prediction was 36.9%. From the variation of solubility with temperature the apparent thermodynamic analysis of dissolution was performed in all the mixtures and neat solvents. Based on the inverse Kirkwood-Buff integrals (IKBI) preferential solvation parameters were calculated. SCM is preferentially solvated by water molecules in water-rich mixtures and also in ethanol-rich mixtures. Further, from densities of the saturated solutions and those of the cosolvent mixtures free of drug, the apparent specific volumes at saturation were also calculated.

Physical Meanings of Fractal Behaviors of Water in Aqueous and Biological Systems with Open-Ended Coaxial Electrodes.

The dynamics of a hydrogen bonding network (HBN) relating to macroscopic properties of hydrogen bonding liquids were observed as a significant relaxation process by dielectric spectroscopy measurements. In the cases of water and water rich mixtures including biological systems, a GHz frequency relaxation process appearing at around 20 GHz with the relaxation time of 8.2 ps is generally observed at 25 °C. The GHz frequency process can be explained as a rate process of exchanges in hydrogen bond (HB) and the rate becomes higher with increasing HB density. In the present work, this study analyzed the GHz frequency process observed by suitable open-ended coaxial electrodes, and physical meanings of the fractal nature of water structures were clarified in various aqueous systems. Dynamic behaviors of HBN were characterized by a combination of the average relaxation time and the distribution of the relaxation time. This fractal analysis offered an available approach to both solution and dispersion systems with characterization of the aggregation or dispersion state of water molecules. In the case of polymer-water mixtures, the HBN and polymer networks penetrate each other, however, the HBN were segmented and isolated more by dispersed and aggregated particles in the case of dispersion systems. These HBN fragments were characterized by smaller values of the fractal dimension obtained from the fractal analysis. Some examples of actual usages suggest that the fractal analysis is now one of the most effective tools to understand the molecular mechanism of HBN in aqueous complex materials including biological systems.

DTAB micelle formation in ionic liquid/water mixtures is determined by ionic liquid cation structure

HypothesisThe high CMCs and low aggregation numbers of ionic micelles in the extreme electrolyte environment of ionic liquids (ILs) seem to be at odds with the effect of dilute aqueous electrolytes, which lower CMCs and promote elongated micelles. We hypothesise that the driving force for micellisation in ILs is determined by their underlying amphiphilic nanostructure, and that this can be controlled by mixing with water. ExperimentsCMCs and micelle sizes of dodecyltrimethylammonium bromide (DTAB) are determined in mixed solvents comprising water and the ionic liquids ethylammonium nitrate (EAN), ethanolammonium nitrate (EtAN), and propylammonium nitrate (PAN) over a wide composition range. Their behaviour is compared with aqueous electrolytes up to their solubility limit. CMCs are determined by a variety of techniques, and their relative strengths critically evaluated. Micelle morphology is determined by small-angle neutron scattering. FindingsIn water-rich mixtures, ILs do behave like simple electrolytes. Counterion binding dominates, both lowering the aqueous CMC and favouring a sphere-rod transition. However, even at modest concentrations, IL cations become incorporated into the micelle, causing the CMC to pass through a minimum, and arresting the sphere-rod transition. The efficiency of the cation depends on its amphiphilicity. As the IL content increases further, its role as a component of the bulk solvent becomes dominant: Only here does IL nanostructure influence micellization, as it increases alkyl chain solubility (EAN, PAN) and hence raises the CMC.