Enthalpy of solution of phenoxyalcohols solubilized in aqueous sodium dodecylsulfate and hexadecyltrimethylammonium bromide solutions

The enthalpy of solution of phenoxy 2-ethanol, 1 phenoxy,-3 propanol and benzylalcohol was determined at 25 °C in aqueous sodium dodecylsulfate and hexadecyltrimethylammonium bromide solution, up to 0.2 mol/kg surfactant concentration. Using the pseudo-phase model, the standard enthalpy of transfer and the partition coefficient of the alcohols between micelle and water are calculated. The latter quantity is found to be systematically larger when derived from enthalpy than from free energy measurements. Using the so-called compensation plot, the solution thermodynamics of aromatic and aliphatic alcohols in aqueous sodium dodecylsulfate and in the octane+water systems are compared. Aromatic alcohols display an anomalous behavior in the octane+ water system but not in the micellar one.The standard enthalpy of solution of various alcohols presents, when plotted against hexadecyltrimethylammonium bromide concentration, a shoulder in the region around 0.05 mol/kg; a discussion is presented on the evidence for alleged micellar structural changes in aqueous micellar systems.     

Extraction of ethylene glycol from aqueous salt solutions

A method is proposed for extracting ethylene glycol from aqueous salt solutions by dialysis through ion-exchange membranes, based on the Donnan exclusion of the electrolyte. Dialysis is performed in the continuous and batch modes. It is found that the batch mode of dialysis is more effective for extracting ethylene glycol from its aqueous salt solutions. The effect of the ionic form of the membrane on ethylene glycol fluxes is explained through computer simulation.     

Critical micelle concentration and self-aggregation of hexadecyltrimethylammonium bromide in aqueous glycine and glycylglycine solutions at different temperatures

Conductivities, densities and ultrasonic speeds measurements of hexadecyltrimethylammonium bromide (HTAB) in aqueous solutions of glycine (Gly) and glycylglycine (Gly-Gly) have been made at various temperatures. The critical micelle concentration (CMC), the degree of ionization (??) of the micelles, standard free energy, enthalpy, and entropy of the micellization process (??G _m ^° , ??H _m ^° , and ??S _m ^° ) for the present systems were estimated at different temperatures. The CMC values of HTAB in aqueous Gly and Gly-Gly were also evaluated by density and ultrasonic speed measurements. Apparent molar volumes, (V _?), apparent molar volumes at infinite dilution, (V _? ^° ), apparent molar compressibilities, (K _?), of HTAB in the pre- and post-micellar regions, and volume change on micellization (??V _? ^m ) were also estimated. Large positive values of T??S _m ^° and small negative values of ??H _m ^° suggest that micellization process is driven primarily by entropy increase. The increase in ??V _? ^m and K _? with rise in temperature is indicative of less compact micellar structure of HTAB in presence of amino acid additives. These data suggest that amino acids are solubilised probably in the palisade layer of the micelle.     

Molar volumes of aqueous and ethylene glycol solutions of tetrahydrofuran

The densities of ethylene glycol solutions of tetrahydrofuran (THF) with 0–20 mol % THF were measured at 20–60°C and atmospheric pressure to an accuracy of 5 × 10⁻⁵ g/cm³. The apparent molar volumes of THF in the solutions were calculated and their concentration and temperature dependences determined. The results were compared with the apparent molar volumes of THF in aqueous systems calculated from the literature data. Minima were found on the concentration dependence of the apparent volume of THF for both aqueous and ethylene glycol solutions and changed differently as the temperature increased. The data obtained were discussed from the standpoint of solvophobic effects in aqueous and ethylene glycol solutions of THF.     

Solubilization of benzene and cyclohexane in aqueous solutions of hexadecyltrimethylammonium bromide: a deuterium magnetic resonance study

Quadrupole splittings in the ²H NMR spectrum from C₆D₆ and C₆D₁₂ solubilized in aqueous solutions of hexadecyltrimethylammonium bromide (CTAB) have been observed in the hexagonal liquid crystalline phase (E) as well as in the concentrated micellar phase (L₁). The order parameter that is obtained for solubilized C₆D₆ is more than two orders of magnitude greater than previously reported from measurements of linear dichroism spectra. Various possibilities for the nature of the solubilization sites are discussed.     

Swelling of polyacrylamide gels in aqueous solutions of ethylene glycol oligomers

Addition of a small amount of ethylene glycol oligomers (OEG), with the number of repeat units y = 2–4, in an aqueous solution leads to the contraction of both linear and cross-linked poly(acrylamide-co-acrylic acid) chains. The results present clear evidence for the screening effect of OEG on the ionic groups of the polymer chains. Measurements indicate that the pre-swollen poly (acrylamide-co-acrylic acid) gels immersed in aqueous OEG solutions are at equilibrium. However, as the molecular weight of OEG increases, these gels cannot attain their equilibrium swelling ratio due to the appearance of non-equilibrium structures. The stability of these structures increases as the initial swelling degree of the gels increases.     

Spectroscopic and computational studies of aqueous ethylene glycol solution surfaces

The combination of Monte Carlo, ab initio, and DFT computational studies of ethylene glycol (EG) and EG-water hydrogen-bonding complexes indicate that experimental vibrational spectra of EG and EG-water solution surfaces have contributions from numerous conformations of both EG and EG-water. The computed spectra, derived from harmonic vibrational frequency calculations and a theoretical Boltzmann distribution, show similarity to the experimental surface vibrational spectra of EG taken by broad-bandwidth sum frequency generation (SFG) spectroscopy. This similarity suggests that, at the EG and aqueous EG surfaces, there are numerous coexisting conformations of stable EG and EG-water complexes. A blue shift of the CH2 symmetric stretch peak in the SFG spectra was observed with an increase in the water concentration. This change indicates that EG behaves as a hydrogen-bond acceptor when solvated by additional water molecules. This also suggests that, in aqueous solutions of EG, EG-EG aggregates are unlikely to exist. The experimental blue shift is consistent with the results from the computational studies.     

Foaming in aqueous solutions of hexadecyltrimethylammonium bromide and silica nanoparticles: Measurement and analysis of rheological and interfacial properties

The properties of aqueous foams stabilized by a mixture of negatively charged silica nanoparticles and hexadecyltrimethylammonium bromide were studied in this work. Rheological properties of the foams were studied. The interaction between nanoparticles and surfactant molecules in the bulk phase was studied by zeta potential and size measurements of the particles. The interaction at the interface was studied by means of interfacial shear rheology, surface pressure measurement, and atomic force microscopy. It was found that foams were more stable at low surfactant concentrations, though the foamability was low. This was due to the formation of a strong viscoelastic film of surfactant-laden particles at the air–water interface. A suitable mechanism has been proposed to explain the stability of foams in the presence of nanoparticles at different surfactant concentrations.     

Solvation of amides of carboxylic acids in aqueous solutions of ethylene glycol

Enthalpies of solution of amides of formic, acetic, and propionic acids with different degrees of N-substitution in aqueous solutions of ethylene glycol were measured at 298.15 K. The concentration of ethylene glycol did not exceed 4 mol kg^–1. The reasons for increasing endothermic values of the enthalpies characterizing the amide transfer from water to a mixed aqueous-organic solvent on going from primary to tertiary amides and from formamides to the corresponding acetamides are discussed. The enthalpic coefficients of pair interactions between amides and ethylene glycol in water were calculated. The endothermicity of the interaction of the alkyl groups of the amide molecules with ethylene glycol results in positive values of the coefficients. The coefficient values increase with the enhancement of the hydrophobic properties of hydrophilic non-electrolytes (urea, formamide, ethylene glycol) due to an increase in the contribution of the hydrophobic component and a decrease in the contribution from the interaction of the polar groups of amides to the total interaction.     

Solubility of amino acids in aqueous poly (ethylene glycol) solutions

The solubilities of amino acids have been measured in water and aqueous poly(ethylene glycol) (PEG) solutions as a function of temperature and PEG concentration. The free energies of transfer from water to aqueous PEG solutions forl-alanine,l-valine,l-isoleucine andl-leucine were positive, while those forl-phenylalanine andl-tryptophan were negative. The corresponding enthalpies of transfer were almost zero for all amino acids. The equilibrium constants of the binding of amino acids to PEG chain were estimated from the solubility data. Amino acids with larger hydrophobicity are bound more strongly to the PEG chain due to the hydrophobic interaction between the methylene groups of PEG and the side chain of amino acid. The equilibrium constants showed a correlation with the dynamic hydration number (n _DHN) which expresses the hydration properties of amino acids in aqueous solution.     

Enthalpy characteristics of L-asparagine interaction with glycerol, ethylene glycol, and 1,2-propylene glycol in aqueous solutions

Integral dissolution enthalpies ??_sol H ^m of L-asparagine in the mixtures of water with glycerol, ethylene glycol, and 1,2-propylene glycol at the concentration of organic solvents up to 0.24 mole fraction were measured by the calorimetry method. The standard enthalpies of dissolution (??_sol H ⁰) and transport (??_tr H ⁰) of amino acids from water to the mixed solvents were derived. The calculated enthalpy coefficients of the molecule pair interactions of L-asparagine-cosolvent are positive, except for the amino acid-glycerol-water system. The data obtained are interpreted in terms of prevalence of different types of interactions in solution and effect of the cosolvent nature on the thermochemical characteristics of the L-asparagine dissolution.     

Thermochemical characteristics of interactions of DL-alanine in aqueous solutions of glycerol, ethylene glycol, and 1,2-propylene glycol

The method of dissolution calorimetry was used to measure the integral enthalpy of dissolution ??_sol H ^m of DL-alanine in mixtures of water with glycerol, ethylene glycol, and 1,2-propylene glycol at a concentration of organic solvent up to 0.32 mole fraction. The standard dissolution enthalpy (??_sol H ⁰) and transport enthalpy of amino acids from water to mixed solvent (??_tr H ⁰) were calculated. The calculated enthalpy coefficients of pair interactions of the DL-alanine molecules with the polyol molecules are positive and less than these values for L-alanine. The effect of interactions of different types in solution and the structural features of biomolecules and co-solvents on the enthalpy of dissolution characteristics of amino acids were considered.     

Thermochemical investigation of interaction of L-serin with glycerol,ethylene glycol,and 1,2-propylene glycol in aqueous solutions

By the method of dissolution calorimetry integral enthalpies of dissolution Δ_sol H ^m of L-serine are measured in the mixtures of water with glycerol, ethylene glycol, and 1,2-propylene glycol at the concentration of the organic solvent up to 0.42 mole fraction. The standard values of enthalpies of dissolution (Δ_sol H ⁰) and transfer (Δ_tr H ⁰) of amino acids from water to mixed solvents are calculated. The calculated values of the enthalpy coefficients of pair interactions of L-serine with the molecules of co-solvents are positive. The data obtained are interpreted in terms of prevalence of different types of interactions in solutions and the influence of nature of co-solvents on the thermochemical characteristics of the dissolved amino acids.     

Conductometric studies of DyCl3 in dilute aqueous solution

The limiting conductivity of Dy³⁺(aq) has been determined for the first time by linear extrapolation of conductivity measured in dilute aqueous solutions of (DyCl₃+HCl) at 25°C as ^o(Dy³⁺, aq) = (62.9±0.7) S-cm²-eq^-1. A second set of conductivity measurements in dilute aqueous solutions of DyCl₃ has given evidence of very slight hydrolysis of the cation, with a first hydrolysis constant of 6 x 10^–8 mol-dm^–3 (pK=7.2±0.5) calculated by applying the Onsager-Kim law of electrolyte mixtures.     

Thermodynamic and optical studies of some ethylene glycol ethers in aqueous solutions at T = 298.15 K

Experimental results of density (ρ), speed of sound (u), and refractive index (n_D) have been obtained for aqueous solutions of ethylene glycol monomethyl ether (EGMME), ethylene glycol monoethyl ether (EGMEE), diethylene glycol monomethyl ether (DEGMME), and diethylene glycol monoethyl ether (DEGMEE) over the entire concentration range at T = 298.15 K. From these measurements, the derived parameters, apparent molar volume of solute (?_V), excess molar volume (V^E), isentropic compressibility of solution (β_S), apparent molar isentropic compressibility of solute (?_KS), deviation in isentropic compressibility (Δβ_S), molar refraction [R]_1,2 and deviation in refractive index of solution (Δn_D) have been calculated. The Redlich–Kister equation has been fitted to the calculated values of V^E, Δβ_S and Δn_D for the solution. The results obtained are interpreted in terms of hydrogen bonding and various interactions among solute and solvent molecules.     

Thermodynamics of hexadecyltrimethylammonium bromide micelle formation

The thermodynamic parameters for CTAB micelle formation (ΔН, ΔG, ΔS) are calculated at different temperatures. Critical micelle concentrations CMC1 are determined. The possibility of determining CMC2 is demonstrated.     

Thermochemical characteristics of the interaction of L-cysteine with glycerol,ethylene glycol,and 1,2-propylene glycol in aqueous solutions

Integral enthalpies of dissolution Δ_sol H ^m of L-cysteine in mixtures of water with glycerol, ethylene glycol, and 1,2-propylene glycol at concentrations of organic solvents of up to 0.37 mole fraction were measured by calorimetry of dissolution. The standard values of the dissolution enthalpies (Δ_sol H°) and the transfer enthalpies (Δ_tr H°) of amino acid from water to the mixed solvent were calculated. It was shown that the calculated enthalpic coefficients of the pair interactions of L-cysteine with cosolvent molecules have positive values. The obtained data are interpreted from the viewpoint of the prevalence of different types of interactions in the solutions and influence of the cosolvents nature on the thermochemical characteristics of amino acid dissolution.     

Crystallization of nordstrandite in ethylene glycol / water solutions: electron microscopic studies

The present work shows the growth of nordstrandite microcrystals observed by transmission and scanning electron microscopy. Nordstrandite was synthesised from non-crystalline aluminium hydroxide reacted in 20% ethylene glycol/water solution, at room temperature. This material was characterized by TEM, SEM, SAED, XRD and EDS/TEM, during six month and revealed the formation and growth of nordstrandite. Fibrillar pseudoboehmite is the only aluminium hydroxide which could be identified during the first two weeks. The nuclei grow, from complete dissolution/recrystallization of pseudoboehmite fibrils, into platy rectangular microscrystals of nordstrandite. Some tabular microcrystals recrystallise, forming after six months only the multi-point nordstrandite stars. This electron-optical study suggest that the star shape results from the overlapping of rectangular plates, and pseudoboehmite fibrils act as the precursor of nordstrandite crystallisation in ethylene glycol/water solution.      

Formation of poly(ethylene glycol) inclusion complexes in aqueous solutions of mixed cyclodextrins

Even though the addition of modified cyclodextrins (modified CDs) accelerates the precipitation in aqueous solutions of poly(ethylene glycol) (PEG) and α-cyclodextrin (α-CD) the final amount of formed solid complex remains unchanged, with no significant presence of modified CDs detected by MALDI-TOF mass spectrometry. Thus unsuitability of kinetic turbidity measurements for determination of binding parameters was confirmed. On the other hand, theoretical calculations based on a model of a chain of freely accessible binding sites demonstrated that the results do not necessarily contradict the finding that individual modified CD molecules can thread onto PEG chains with the efficiency comparable to that of natural (unmodified) α-CD.