Heat capacities and volumes of interaction between mixtures of alcohols in water at 298.15 K

The heat capacities and densities of mixtures of aqueous solutions of normal alcohols (methanol to n-butanol) and t-butanol were measured at 298.15 K at low molalities. The results were used to calculate the thermodynamic pair and triplet interaction parameters between solutes for heat capacities and volumes. The pair parameters are approximately a linear function of the total number of carbon atoms of the two solutes. The enthalpic pair and triplet interaction parameters for (ROH + H₂O) are also reported. The temperature dependence of the pair parameters for Gibbs free energies, enthalpies, entropies, heat capacities, and volumes are discussed in terms of structural changes in the aqueous solutions.     

Polythermal solubility of chromium(III) and cobalt(III) tris(acetylacetonates) in water-tert-butanol mixtures

Solubility data for chromium(III) and cobalt(III) tris(acetylacetonates) in water and water-tert-butanol mixtures over a wide range of temperatures and alcohol concentrations were obtained, and thermodynamic parameters of solution were calculated. The dependences of solubility on the concentration of tert-butanol have an inversion point corresponding to a change in the hydration mechanism, when the solvent structure changes from water to aqueous alcohol.     

Dehydration of glycine in mixed solvents

The analysis of changes in the partial volume of glycine $\Delta \bar V^0 $ in solutions of substances that have a different effect on water structure is presented. For glycine in mixtures of water with glycerol and ethylene glycol, we derive a single equation for the $\Delta \bar V^0 $ dependence on the volume fraction of alcohol. The addition of tert-butyl alcohol, ethylene glycol, glycerol, and urea to water leads to a decrease in the hydration number of the amino acid (glycine dehydrates). In 1m solutions the losses of hydration water are 3.2%, 4.5%, 5.7%, and 7.6% respectively. In a 4m solution of tert-butyl alcohol, glycine loses 44% of hydration water, the same as in a 15m urea solution and a 20m glycerol solution. A contribution of the structural dehydration of glycine is observed in dilute aqueous solutions of t-BuOH. In more concentrated solutions, intermolecular interactions in the binary mixed solvent counteract dehydration. These interactions compensate for 15-22% of water lost by glycine in a 20m solution of urea, glycerol, and ethylene glycol and a 4m solution of t-BuOH. The partial volumes are also discussed within preferential solvation concepts.     

“Order-disorder” transition model in aqueous solutions of aliphatic alcohols

A model of “order-disorder” type structural transitions in dilute aqueous solutions of lower aliphatic alcohols is proposed. Analytical expressions for the thermodynamic potential of the solution, its isobaric heat capacity increment, and the dependence of the temperature of a solution transition to a structurally ordered state on the alcohol concentration are obtained. A linear correlation between the concentration dependence of the heat capacity and the compressibility of the solution is proved to exist.     

Thermodynamics of glycine solution in aqueous urea. Rule \sqrt m

The solution heats of glycine in aqueous urea have been determined by calorimetry at 298 K (molality 0–13) and 313 K (molality 0–22). The solution heat of the amino acid is described by the linear dependence of this quantity on the square root of the urea molality. The enthalpy, entropy, and Gibbs energy of the transfer of glycine from water to aqueous urea, as well as the heat capacity, entropy variation, and Gibbs energy of glycine solution have been calculated for the temperature range 273–323 K. It is found that urea additions to water reverse the sign of the heat capacity of solution.     

Rate and thermodynamic studies of the interaction between water and iso-butyl cellosolve by ultrasonic methods

Ultrasonic absorption and velocity measurements in aqueous solution of iso-butyl cellosolve (ethylene glycol iso-butyl ether) as a function of the concentration are reported. The two relaxational absorptions have been attributed to the perturbation of the equilibria expressed by AB?A+B and Aα(1/n)A_n where A is the solute, B is the solvent, AB is the complex and A _n is the solute aggregate. The rate constants for each step have been determined. From the concentration dependence of the maximum excess absorption per wave length, the enthalpy change and the volume change for the reaction between the solute and the solvent have been determined for aqueous solutions of butyl cellosolve (ethylene glycol n-butyl ether), iso-butyl cellosolve and propyl cellosolve (ethylene glycol n-propyl ether). The results are consistent with a hydrogen bonding reaction. The effect of the ethers on water structure are considered and it is clear that the fraction of water molecules which can hydrogen bond to the solute decreases with the increasing hydrophobicity of the solute.     

Thermodynamic properties of ternary mixtures containing water, 2-ethoxyethanol,and <Emphasis Type="Italic">t</Emphasis>-butanol at 298.15 K

Ultrasonic speeds and isentropic compressibilities were measured at 298.15 K in the water-rich region of aqueous solutions of water + 2-ethoxyethanol (2EE) + t-butanol. The excess properties of ultrasonic speed and isentropic compressibility were also calculated and have been discussed in terms of molecular interactions. The concentrations of t-butanol at which ultrasonic speed becomes maximum and isentropic compressibility becomes minimum are found to decrease with increase in the concentration of 2EE in the cosolvent (aqueous 2EE). This behavior indicates that the aqueous ternary solutions are less structured than aqueous t-butanol. This behavior is explained as due to a decrease in the ability of t-butanol to form clathrate hydrates owing to the presence of 2EE. When the concentration of 2EE in the cosolvent (x _2EE) > 0.14, ultrasonic speed decreases and isentropic compressibility increases with concentration of t-butanol indicating that the ternary solution behaves as normal solution wherein any further addition of 2EE or t-butanol leads to destabilization of the hydrogen bonded structure of water and t-butanol looses its ability to form clathrate hydrates in aqueous solutions.     

Vapor Pressure Osmometry and Its Applications in the Osmotic Coefficients Determination of the Aqueous Monomer Glycol and Polymer Polyethylene Glycol Solutions at Various Temperature

Based on the principle and calibration of vapor pressure osmometer and its application in the thermodynamics of the aqueous solutions, the results on aqueous solution of monomer glycol,PEG200,PEG400,PEG1500 and PEG2000 over the different concentration range at various temperatures were reported.Using a linear least-square fitting routing,the osmotic coefficients were fitted by a simple polynomial equation.It was found that the relationship between the molar osmotic coefficients (Φ） and the molar concentration(c) of the solutions are in a quite good agreement with the fitted polynomial equation at various temperatures over the different concentration range.The experimental results also show that over the studied concentration range and at various temperatures,the concentration dependence of the molar osmotic coefficients of the aqueous solution systems with the solutes of PEG200,PEG400,PEG1500 and PEG2000 are totally presented in a rising tend,and their temperature dependence of the osmotic coefficients of the aqueous solution systems of the molar concentration exhibits their own regularities,respectively.The aqueous glycol solution system exhibits the properties of the dilute solution.     

Thermodynamic characteristics,structure, and interactions of L-proline in aqueous solutions of alcohols and urea

The enthalpies of dissolution of imino acid L-proline in aqueous solutions of methanol, 2-propanol, ethylene glycol, glycerin, and urea are measured by the calorimetric method at 313.15 K. Enthalpic parameters of the interaction of L-proline with nonaqueous components are calculated and compared with the data at 298.15 K. It is found that the sign of the heat capacity parameter of the pair and ternary interactions depends on whether the nonaqueous solvent component is a destroyer or stabilizer of the water structure. Partial molar heat capacities of proline in mixed solvents are obtained by the integral dissolution heat method. Temperature changes in the reduced enthalpy and entropy of the proline solution are determined at an increase in the temperature from 298 K to 313 K. It is shown that there is entropyenthalpy compensation at temperature changes in the characteristics during dissolution.     

Enthalpies of solution in sodium octanoate + water + alcohol mixtures

Enthalpies of solution of sodium octanoate in water, 1-propanol and aqueous mixtures of 1-propanol, 1-butanol, 1-pentanol and 1-hexanol, and of the alcohols in aqueous solutions of sodium octanoate at various concentrations were determined calorimetrically at 35 °C. MostH(soln) values are exothermic and strongly dependent on the solute concentration. The main energetic factor governing the process of dissolution of the surfactant is associated with changes in the water structure caused by the presence of alcohol. That governing the process of the alcohol dissolution in surfactant solutions is due to the effect alcohols have on the CMC of the octanoate. There is no indication of the alcohol being either solubilized in the interior of the aqueous micelle, or becoming part of the micellar film.The solubility at 35 °C of sodium octanoate in water, 1-propanol and their mixtures has also been determined.     

Micellar behavior of some amphiphilic block polyurethanes in aqueous/nonaqueous media

Amphiphilic polyether block polyurethanes based on Pluronic type macrodiol and polyethylene glycol as co-segment have been prepared. Their micellar behavior in N,N-dimethylformamide solution, aqueous solvent mixtures and with added inorganic salts or urea was investigated by employing fluorescence spectroscopy and tensiometry techniques. Increased values of the critical micelle concentration were found for the more soluble block copolyurethane. The structural components have a strong influence on micellar characteristics of the studied systems.     

UCST and LCST phase behavior of poly(trimethylene ether) glycol in water

We describe the initial studies of the complex aqueous phase behavior of poly(trimethylene ether) glycol (PO3G), a renewably sourced polyether glycol. Cloud point measurement revealed that a low molecular weight PO3G exhibits both lower critical solution temperature (LCST) and upper critical solution temperature (UCST) in water in the temperature range between 30°C and 80°C. At low concentrations of PO3G, the polymer solutions exhibit LCST‐type phase behavior. In the intermediate concentration ranges, PO3G and water are immiscible. However, at higher concentrations of PO3G, the solutions show UCST‐type phase behavior. In addition, both the LCSTs and UCSTs can be easily tuned over a wide range by varying the amount of alcohol co‐solvents. These findings have potential applications in the design of personal care applications and in the development of thermosensitive “smart” materials. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

N,N-bis-(2-benzimidazolylmethyl)L-methionine: An efficient Ag(I) extractant

A new ligand N,N-bis-(2-benzimidazolylmethyl)L-methionine has been synthesized and well characterized by different analytical techniques. The ligand has a very strong affinity for silver(I) and is used for the selective extraction of silver ions from aqueous solution into 1-butanol. The effect of concentration of Ag(I), pH, diverse ions, and temperature on the extraction is reported. The developed method has success-fully been applied to the determination of silver in different samples. Radiotracer technique, using ^110mAg(I) as a tracer, has been used for monitoring the concentration of silver ion.     

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.     

Partial molar enthalpies of solution as indicators of interactions in mixtures of 2-butoxyethanol and 2-butanol with water

Calorimetric measurements have been made of differential enthalpies of solution of both components in the binary system 2-butoxyethanol-water and of 2-butanol in the system 2-butanol-water as a function of composition at three different temperatures. The heat capacity changes for dissolution were calculated from the temperature variation of the solution enthalpies. Drastic changes of the solution properties are seen with increasing solute concentration in water-rich solutions. In the 2-butoxyethanol-water system, which could be studied over the whole composition range, four different regions can be identified. At extreme dilution in water, the solute is fully hydrated with a primary hydration layer of monolayer thickness involved in long-range secondary hydration. In dilute solutions the primary hydration layer is unchanged but the secondary hydration diminishes with increasing solute concentration. In semi-dilute solution the primary hydration layer breaks down and the particular hydrophobic characteristics of hydrocarbon groups in aqueous solution disappear. At higher solute content the mixtures show no hydrophobic character but the behavior of regular mixtures of polar solutes.     

Bulk properties of a liquid phase mixture {ethylene glycol+<Emphasis Type="Italic">tert</Emphasis>-butanol} in the temperature range 278.15–348.15 K and pressures of 0.1–100 MPa. II. Molar isothermal compressibility,molar isobaric expansibility,thermal pressure coefficient,and internal pressure

Based on the experimental data, the molar isothermal compressibilities, molar isobaric expansibilities, thermal pressure coefficients, internal pressures of a liquid phase mixture {ethylene glycol (1) + tert-butanol (2)} are calculated for a wide spectrum of compositions in the range of pressures of 0.1–100 MPa and temperatures of 278.15–323.15 K. Shown that the dependences of molar isothermal compressibilities K _{T, m} , molar isobaric expansibilities E _{P, m} , and isochoric thermal pressure coefficients β on the mole fraction of tert-butanol in the mixture are characterized by the absence of extrema typical of aqueous systems. The manifestation of negative partial expansibility and negative partial expansibility of ethylene glycol in the mixture is found. The thermal pressure coefficients decrease with an increase in the mole fraction of tert-butanol at all pressures and temperatures. A rise in the pressure increases the thermal pressure coefficient, while a rise in the temperature decreases its value due to a decrease of free space in the mixture. An increase in the concentration of tert-butanol leads to an increase in the negative temperature coefficient of internal pressure ΔP _int/ΔT, which indicates a weakening of intermolecular interaction at these compositions.     

Mass action model for solute distribution between water and micelles. Partial molar volumes of butanol and pentanol in dodecyl surfactant solutions

The densities of 1-butanol and 1-pentanol were measured in aqueous solutions of dodecyltrimethylammonium bromide and dodecyldimethylamine oxide and the partial molar volumes at infinite dilution of the alcohols in aqueous surfactants solutions were obtained. The observed trends of this quantity as a function of the surfactant concentration were rationalized using a mass-action model for the alcohol distribution between the aqueous and the micellar phase. At the same time, the model was revised to account for the alcohol effect on the surfactant micellization equilibrium. The partial molar volume of alcohols in the aqueous and in the micellar phases and the ratios between the binding constant and the aggregation number were calculated. These thermodynamic quantities are nearly the same in the two surfactants analyzed in this paper but differ appreciably from those in sodium dodecylsulfate. The apparent molar volume of surfactants in some hydroalcoholic solutions at fixed alcohol concentration were also calculated. In the micellization region the trend of this quantity as a function of the surfactant concentration shows a hump, which depends on the alcohol concentration and on the alcohol alkyl chain length. The alcohol extraction from the aqueous to the micellar phase due to the addition of the surfactant can account for the observed trends.     

Diffusive dynamics of water in tert-butyl alcohol/water mixtures

Quasielastic neutron scattering has been used to investigate the dynamical behavior of H(2)O in water/tert-butyl alcohol solutions. The measurements were made at fixed temperature (293 K) as a function of tert-butyl alcohol molar fraction, x, in the range 0-0.042. The data have been compared to those of pure water in the temperature range 269-293 K. The effect of tert-butyl alcohol addition on water dynamics is equivalent to that obtained by lowering the temperature of pure water by an amount proportional to the alcohol concentration. The temperature dependence of the diffusivity parameters in pure water and their concentration dependence in tert-butyl alcohol/water solutions can be rescaled to a common curve attributing to each solution a concentration-dependent "structural temperature" lower than the actual thermodynamic one. These results can be understood in terms of Stillinger's picture of water structuring and of other more recent theoretical pictures that emphasize the influence of the geometrical properties of hydrogen bond networks on water mobility.     

Dynamical properties of ethylene glycol and glucose studied by temperature-modulated differential scanning calorimetry and Brillouin scattering

The fragility of ethylene glycol and glucose aqueous solution systems has been investigated by temperature-modulated differential scanning calorimetry (TMDSC). The frequency and temperature dependences of complex specific heat have been observed in the vicinity of a glass-transition temperature T _g . It is shown that the value of the fragility index m can be determined from the temperature dependence of the α-relaxation times observed by TMDSC. We have also studied the elastic properties of these aqueous solutions by micro-Brillouin scattering, and determined these relaxation times of elastic properties in the gigahertz range.     

Self-assembly of graphene oxide nanosheets in t-butanol/water medium under gamma-ray radiation

Graphene oxide (GO) nanosheets dispersed in strong acidic t-butanol/water medium can be reduced and self-assembled into a self-standing graphene hydrogel under γ-ray radiation, providing a facile and economical preparation method for hydroxylalkylated graphene-based aerogel.