Binding constants and partial molar volumes of primary alcohols in sodium dodecylsulfate micelles

The densities of methanol, ethanol, 1-propanol, 1-butanol and 1-hexanol were measured in aqueous solutions of sodium dodecylsulfate at 25°C. The partial molar volumes of the alcohols at infinite dilution in the aqueous surfactants solutions were calculated and discussed using a mass-action model for the alcohol distribution between the aqueous and the micellar phase. The partial molar volumes of the alcohols in the aqueous and in the micellar phases, and the ratios between the binding constant and the aggregation number, were calculated. The partial molar volume for all the alcohols in micellar phase is 10 cm³-mol^–1 smaller than that in octane. This can be related to the strong hydrophilic interaction between the head groups of the alcohol and the micellized surfactant. From the extrapolated values of the distribution constant and the partial molar volumes in the aqueous and micellar phases, the standard partial molar volume of heptanol in micellar solutions was found to decrease with increasing surfactant concentration. The standard free energy of transfer of alcohols from water to micelles was rationalized in terms of hydrophilic and hydrophobic contributions. A model is proposed in which the empty space around each solute is assumed to be the same in the gas and liquid phases, and is used to explain the behavior of micelles in the presence of amphiphilic solutes.     

Thermodynamics of mixed micellar systems of sodium octanoate and ethoxylated alcohols in water at 25°C

Thermodynamic volume and compressibility properties of binary aqueous systems of sodium octanoate (C₈Na) and polyoxyethylene butyl ether compounds (ethoxylated alcohols), with one to three oxyethylene groups (C₄EO_X), and ternary systems of these compounds, have been determined as a function of surfactant and alcohol concentrations at 25°C from density and ultrasonic velocity measurements. Values of standard state apparent molar volume and apparent molar adiabatic compressibility properties of transfer of ethoxylated alcohols from water to aqueous C₈Na solutions were obtained. The observed trends in the properties of the aqueous binary C₈Na systems and of the transfer functions for C₄EO_x, at a given low concentration of 0.05m, were analyzed using theoretical models. Good agreement between the simulated results and the experimental data was achieved. The results obtained for the distribution coefficients of the alcohols and the thermodynamic properties of both components of the mixed micelle show that the hydrophobicity of the ethoxylated alcohols is enhanced by introducing more oxyethylene groups into the alcohol. The distribution behavior of these compounds between the C₈Na micelles and the aqueous phase also depends on the difference between the hydrophobicity of the surfactant and the alcohols.     

Enthalpies and heat capacities of transfer of sodium carboxylates and sodium dodecylsulfate from water to aqueoustert-butyl alcohol solutions

Integral enthalpies of solution at very low concentrations of sodium carboxylates and sodium dodecylsulfate in aqueous tert-butyl alcohol solutions at 25°C and 35°C were measured with an isoperibol submarine calorimeter. The enthalpies and heat capacities of transfer of these surfactants from water to aqueous tertbutyl alcohol solutions were derived from integral enthalpies of solution. The results are explained in terms of the structural alteration effect of the constituent hydrophobic and hydrophilic groups of the solute.     

Enthalpies of solution of l-threonine in a (water + alcohol) mixture at 298.15 K

The enthalpies of solution of l-threonine in the (water + methanol), (water + ethanol), (water + n-propanol), and (water + i-propanol) mixtures, with an alcohol content up to 0.4 mol fractions, have been measured calorimetrically at T = 298.15 K. The standard enthalpies of solution and transfer of l-threonine from water to an aqueous alcohol have been calculated. The effect of the structure properties of the mixed solvent on the specified enthalpy characteristics of l-threonine is discussed. The enthalpy coefficients of pairwise interactions between amino acid and alcohol molecules have been computed. It has been found that these coefficients become increasingly positive in the methanol, ethanol, n-propanol, and i-propanol consequence. A comparative analysis of the thermodynamic characteristics of dissolution of l-threonine and some other amino acids (glycine, l-alanine and l-valine) in the mixtures studied has been made.     

1-丁基-3-甲基咪唑六氟磷酸盐+水+醇体系的相行为

在298.15 K, 常压下研究了1-丁基-3-甲基咪唑六氟磷酸盐([bmim][PF₆])+水+甲醇、[bmim][PF₆]+水+乙醇、[bmim][PF₆]+水+2-丙醇、[bmim][PF₆]+水+1-丙醇三元体系的相行为. 结果表明, 对于含甲醇、乙醇和2-丙醇的体系, 醇在水+醇溶液中摩尔分数分别为0.55-1.00、0.40-0.75 和0.35-0.50 时, 醇的水溶液与[bmim][PF₆]可以互溶. 而水+1-丙醇体系没有此类现象. 这说明, 这类三元系的相行为不但取决于醇分子的大小, 而且取决于其结构.     

Excess enthalpies of binary solvent mixtures of N-methylacetamide with aliphatic alcohols

The molar excess enthalpies H _m ^E of binary solvent mixtures of N-methylacetamide with methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and t-butanol have been measured with a flow microcalorimeter at 40°C. The excess enthalpies are negative for methanol and positive for the other alcohols over the whole composition range, except for t-butanol which exhibits a sigmoid curve with a deep minimum at low mole fractions of the amide. The values for the primary alcohols increase in the order methanol < ethanol < 1-propanol < 1-butanol. The partial molar excess enthalpies have also been evaluated. Intermolecular interactions in these mixtures are discussed through comparison of the results with those for the corresponding binary mixtures of N,N-dimethylacetamide.     

Enthalpies of 1,4-Dioxane, 1,2-Dimethoxyethane, and Ethylacetate Solvation in the Water–1-Propanol and Water–Glycerol Binary Mixtures

The enthalpies of 1,4-dioxane, 1,2-dimethoxyethane, and ethylacetate solution in binarymixtures of water with 1-propanol and glycerol were measured at 25°C using a precise isoperibol calorimeter. The enthalpies of the solute solvation were calculated and compared with the experimental data for other solutes. The results obtained were interpreted in terms of universal and specific solute solvation using parameters of a solvent polarity. It was found that the extreme shape of the curve _solv H° vs. X for ethylacetate in the mixtures of water with 1-propanol results from peculiarities of carbotylate-group solvation and appears to be not connected with the influence of alcohol microaggregates in the mixed solvent.     

The association of aromatic anions in water

Molar conductances of dilute solutions of sodium 2-naphthalenesulfonate at 25°C and of sodium 2-anthraquinonesulfonate have been measured at 25 and 37°C. These data are interpreted to show that the anthraquinonesulfonate anion is dimerized in solution. Dimerization constants and the enthalpy and entropy of dimerization are calculated. Spectrophotometric absorbancies have been measured at 25, 30, 35 and 40°C for a series of aqueous solutions containing both sodium 4-dimethylaminobenzenesulfonate and sodium 3-nitrobenzenesulfonate. Equilibrium constants and enthalpy and entropy changes for formation of the 1 1 complex between these two ions have been calculated from these data. The formation of these complexes between like-charged ions, and of dimers of other aromatic solutes in water is discussed in terms of a two-state model of hydrophobic hydration.     

Dissolution enthalpies of L-proline and its interactions with methanol, 2-propanol,ethylene glycol,and glycerin in aqueous solution at 298.15 K

The dissolution enthalpies of L-proline in mixtures of water with methanol, 2-propanol, ethylene glycol, and glycerin were measured calorimetrically at 298.15 K. The enthalpy coefficients of the interaction of proline with alcohols in aqueous solutions were determined. The enthalpy coefficients of the pair interaction of proline and glycine with alcohols were shown to be directly proportional.     

Thermochemistry of glycyl-<Emphasis Type="Italic">DL</Emphasis>-α-alanine dissolution in water-alcohol solutions at 298.15 K

Integral enthalpies of glycyl-DL-α-alanine dissolution in aqueous solutions of ethanol, 1-propanol, and 2-propanol at concentrations of alcohols up to 0.4 mol fraction were measured by the calorimetry method. Standard values of the enthalpies of the peptide dissolution Δ_sol H ⁰ and transfer Δ_tr H ⁰ from water in mixed solvents were calculated. Dependences of the thermochemical characteristics of glycyl-DL-α-alanine dissolution on the concentration of cosolvents are of an extreme character. Within the limits of McMillan-Mayer’s theory enthalpy coefficients of pairwise interactions (h _xy ) of the studied compound with molecules of alcohols were calculated. They have positive values increasing in the series ethanol, 1-propanol, 2-propanol. The effect of the structure of dipeptides and composition of water-alcohol solvents on the dissolution enthalpy characteristics was considered on the basis of the obtained experimental and calculated data.     

Standard partial molar volumes of alcohols in aqueous dodecyltrimethylammonium bromide solutions

Density measurements of water-dodecyltrimethylammonium bromide (DTAB)-alcohol ternary systems as a function of alcohol and surfactant concentrations were carried out at 25°C. The alcohols were propanol (PrOH), 2-propanol (2-PrOH) and hexanol (HexOH). The apparent molar volume V_,R of alcohols have been calculated and the standard (infinite dilution) partial molar volumes of alcohols V _R at each surfactant concentration were obtained by means of a least squares fit of V_,R vs. the alcohol concentration. The V _R vs. surfactant concentration curves have been rationalized in terms of the partial molar volume of alcohol in the aqueous V _f and the micellar V _b phases and the distribution constant of alcohol between the aqueous and the micellar phases K. The V _b values for PrOH and HexOH together with those of butanol and pentanol previously reported satisfy the additivity rule giving a methylene group contribution of 16.7 cm³-mol^–1 which is identical to that reported in the literature from the study of pure liquid alcohols. No difference between V _b for PrOH and 2-PrOH has been found. From density data of water-alcohol and water-surfactant binary systems and of water-surfactant-alcohol ternary system, the apparent molar volume of the surfactant in the water-alcohol mixed solvent V_,S have been calculated as a function of the surfactant concentration and of the mixed solvent composition. The effect of the alkyl chain length of the alcohols and the effect of isomerization of the alcohols on the V_,S vs. surfactant concentration trends have been analyzed.     

Effect of anionic surfactant and short-chain alcohol mixtures on adsorption at quartz/water and water/air interfaces and the wettability of quartz

Measurements of the advancing contact angles for aqueous solutions of sodium dodecyl sulfate (SDDS) or sodium hexadecyl sulfonate (SHS) in mixtures with methanol, ethanol, or propanol on a quartz surface were carried out. On the basis of the obtained results and Young and Gibbs equations the critical surface tension of quartz wetting, the composition of the surface layer at the quartz-water interface, and the activity coefficients of the anionic surfactants and alcohols in this layer as well as the work of adhesion of aqueous solutions of anionic surfactant and alcohol mixtures to the quartz surface were determined. The analysis of the contact angle data showed that the wettability of quartz changed visibly only in the range of alcohol and anionic surfactant concentration at which these surface-active agents were present in the solution in the monomeric form. The analysis also showed that there was a linear dependence between the adhesion and the surface tension of aqueous solutions of anionic surfactant and alcohol mixtures. This dependence can be described by linear equations for which the constants depend on the anionic surfactant and alcohol concentrations. The slope of all linear dependence between adhesion and surface tension was positive. The critical surface tension of quartz wetting determined from this dependence by extrapolating the adhesion tension to the value equal to the surface tension (for contact angle equal zero) depends on the assumption whether the concentration of anionic surfactant or alcohol was constant. Its average value is equal to 29.95mN/m and it is considerably lower than the quartz surface tension. The positive slope of the adhesion-surface tension curves was explained by the possibility of the presence of liquid vapor film beyond the solution drop which settled on the quartz surface and the adsorption of surface-active agents at the quartz/monolayer water film-water interface. This conclusion was confirmed by the work of adhesion of aqueous solutions of anionic surfactants and short-chain alcohol mixtures to the quartz surface determined on the basis of the contact angle data and molar fraction of anionic surfactants and alcohols and their activity coefficient in the surface layer.     

The enthalpies of solution and crystallization of sodium nitrate in water at 25°C

The differential enthalpies of solution of sodium nitrate in water have been measured calorimetrically at 25°C, from 0.5 to 10.4 mol (kg H₂O)^–1. The concentration dependence is described by the equation H=20.4537+1.0562m^1/2-7.0568m+2.8659m^3/2-0.3382m² From the calorimetric measurements, the enthalpy of crystallization of sodium nitrate was calculated as H_c=9.98±0.16 kL-mol^-1. The literature data on the solubility, activity and osmotic coefficients of NaNO₃ at 25°C yielded a value of –9.98±0.38 kJ-mol^–1. The good agreement between the experimental and calculated H_c values indicate the reliability of the input data.     

Microheterogeneity in aqueous-organic mixtures: thermodynamic transfer functions for benzene from water to 2-propanol aqueous systems at 25°C

The solubilities, enthalpies of solution, heat capacities, densities and ultrasonic velocities of benzene in 2-propanol-water mixtures were measured at 25°C. The apparent molal volumes, heat capacities and isentropic compressibilities and the free energies, enthalpies and entropies of transfer of benzene were calculated. The benzene concentration is sufficiently low that all thermodynamic quantities can be considered in the standard state. All these functions show large changes in the aqueous end. Large extrema are observed for 2-propanol mole fractions (X_P) near 0.08, and at higher X_P the functions rapidly tend to the values in pure 2-propanol. The free energy of transfer of benzene from water to alcohol-water mixtures decreases linearly with the alcohol concentration up to X_P of 0.07 and then more abruptly. On the other hand, at low temperature, this free energy becomes positive at low X_P. These data are consistent with the existence of microphases in 2-propanol-water mixtures for X_p>0.1. At low X_P benzene is in an aqueous medium but beyond this critical region dissolves preferentially in the organic microphases. Benzene also enhances the formation of 2-propanol microphases and this leads to the observed extrema near X_p=0.08.     

Volumes and heat capacities of some watersurfactant-alcohol ternary systems

The densities and volumetric heat capacities of urea and alcohols were measured in aqueous solutions of octylammonium bromide (OABr) and of OABr in aqueous urea and alcohol solutions. The alcohols studies were methanol, ethanol, 1-propanol, 2-propanol, n-butanol, t-butanol, n-pentanol, n-hexanol and 2-butoxyethanol (BE). In most experiments, the concentration of the reference solute was kept low, and volumes and heat capacities of transfer from water to the mixed solvent were calculated. A more complete study was made with the system BE-OABr-H₂O where both solutes were systematically changed. The observed trends in the thermodynamic functions can be explained through three effects: interactions between the reference solute and the cosolvent in the premiceller region of the surfactant or pre-aggregation region of the alcohol, a distribution of the reference solute between water and the micelle or microphase and an equilibrium displacement of the system, monomer-aggregate, in the vicinity of the reference solute.     

Thermodynamics of ionization of aqueous sulfamic acid,an almost-strong electrolyte

We have measured enthalpies of dilution of aqueous sulfamic acid solutions at 25°C and used results of these measurements to calculate the standard enthalpy of ionization of sulfamic acid. The average H _1on ⁰ obtained in this work was 735±200 J-mol^–1. We have also measured enthalpies of solution of crystalline sulfamic acid in water at 25°C. The results from both measurements are combined with some earlier results from Wu and Hepler to obtain a best value for the standard enthalpy of solution, H _S ⁰ =19.2±0.2 kJ-mol^–1.     

Enthalpies of dilution of mono-, di- and poly-alcohols in dilute aqueous solutions at 298.15 K

The enthalpies of dilution of aqueous solutions of methanol, ethanol, l-propanol, 2-propanol, 1-butanol, l-pentanol, 1-hexanol, cyclohexanol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol and poly-alcohol(cyclohexaamylose) have been determined at high dilution as a function of the mole fraction of alcohol at 298.15 K, by a rocking twin-microcalorimeter of the heat-conduction type. A smoothing equation of the enthalpies of dilution against the mole fractions of alcohols are given. The graphical comparison of experimental results with their smoothed values or literature ones, taking into account the dependence of the mole fractions, are also presented. It has been found for the aqueous solutions of shorter n-alcohols than hexanol that at very high dilution, exothermic values of molar enthalpies of dilution from a definite mole fraction of alcohols to infinite dilution with the change of mole fraction is proportional to carbon number of n-alcohols. The molar enthalpies of infinite dilution of aqueous butanediol isomers and 1-hexanol were very large. Molar enthalpies of infinite dilution of aqueous poly-alcohol (cyclohexaamylose) were endothermic. This revised version was published online in August 2006 with corrections to the Cover Date.     

A comparative study of the volumetric properties of dilute aqueous solutions of 1-propanol, 1,2-propanediol, 1,3-propanediol, and 1,2,3-propanetriol at various temperatures

Excess molar volumes and partial molar volumes were determined for dilute aqueous solutions of 1-propanol, 1,2-propanediol, 1,3-propanediol, and 1,2,3-propanetriol, at temperatures of (283.15, 288.15, 293.15, 298.15, 303.15, and 308.15) K from density measurements. The infinite dilution partial molar volumes of alcohols in aqueous solution were obtained by extrapolation at each temperature. The volumetric behavior of aqueous alcohol and polyol solutions is discussed in terms of the relationship between polar and non-polar groups and its effect on water structure.     

Effect of lower alcohols on adsorption characteristics of sodium dodecyl sulfate solutions at liquid-gas interfaces

The dynamics of a decrease in the surface tension is studied for aqueous solutions of sodium dodecyl sulfate and its mixtures with lower alcohols (ethanol and n-propanol). Two approaches are analyzed as applied to the estimation of the adsorption of two surfactants from their mixed solutions at a liquid—gas interface, i.e., the Frumkin generalized model and the Fainerman—Miller model. It is shown that both approaches adequately describe the concentration dependences experimentally measured for the surface tension of sodium dodecyl sulfate—lower alcohol mixtures.     

Solubility of tris(acetylacetonato)cobalt(III) in micelles. Comparative study of sodium alkylsulfates and alkyltrimethylammonium bromides

The solubility of tris(acetylacetonato)cobalt(III) [Co(acac)₃] has been measured in aqueous surfactant solutions of sodium decylsulfate (NaDeS), dodecylsulfate (NaDS), and tetradecylsulfate (NaTS), and dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB), and hexadecyltrimethylammonium bromide (CTAB) at 35°C. The solubility increases in the order DTABTTABCTAB3. The importance of the surface solubilization is suggested. The results are compared with those for other solubilizates.