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.     

Densities of solutions of four fluoroalcohols in water

Densities of aqueous solutions of four fluoroalcohols have been measured. Apparent and partial molar volumes of the alcoholic components and the excess volumes of mixing have been calculated, and are compared with the corresponding results for alkanols. A linear correlation exists between the volumes and heat capacities of transfer of alcohols from the pure liquids to aqueous solution at infinite dilution. The lines differ for alkanols and fluoroalcohols. Solute-solvent interactions involving fluoroalcohols and water and involving alkanols and water have a different influence on the structural organization of water molecules adjacent to the alcohol solute.     

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.     

Application of a chemical equilibrium model to thermodynamic functions of transfer of alcohols from water to aqueous surfactants

In ternary aqueous solutions, hydrophobic solutes such as alcohols tend to aggregate with surfactants to form mixed micelles. These systems can be studied by meas of the functions of transfer of hydrophobic solutes from water to aqueous solutions of surfactant. These thermodynamic functions often go through extrema in the critical micellar concentration (CMC) region of the surfactant. A simple model based on interactions between surfactant and hydrophobic solute monomers, on the distribution of the hydrophobic solute between water and the micelles and on the shift in the CMC induced by the hydrophobic solute, can simulate the magnitude and trends of the transfer functions using parameters which are mostly derived from the binary systems. In order to check the model more quantitatively, volumes and heat capacities of transfer of alcohols from water to aqueous solutions of a nonionic surfactant, octyldimethylamine oxide, were measured. A quantitative agreement was achieved with three adjustable parameters. Good fits are also obtained for the transfers to the ionic surfactants, octylamine hydrobromide and sodium dodecylsulfate. When the equilibrium displacement contribution is small, the distribution constants and the partial molar properties of the alcohols in the micellar phase agree well with the parameters obtained with similar models.     

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.     

Heat capacities of butanol and pentanol in aqueous dodecyltrimethylammonium bromide solutions

Heat capacities of the ternary systems water-dodecyltrimethylammonium bromide (DTAB)-butanol and water-DTAB-pentanol were measured at 25°C. The standard partial molar heat capacities of pentanol in micellar solutions show a maximum at about 0.35 mol-kg^–1 DTAB that has been attributed to a micellar structural transition. This maximum tends to vanish by increasing the alcohol concentration and by decreasing the alcohol alkyl chain length; in the case of butanol it was not detected. The behavior of the standard partial molar heat capacities of alcohols in micellar solutions in the region above the cmc and below the structural transition was explained using a previously reported mass-action model for the alcohol distribution between the aqueous and the micellar phase and the pseudophase transition model for micellization. In the resulting equation the contributions due to the temperature effect on the shift of both the micellization equilibrium and the distribution are shown to be negligible so that only the distribution effect and the shift of the micellization equilibrium due to the added alcohol remain. The distribution constant and the partial molar heat capacities of alcohols in the aqueous and micellar phases have been derived by linear regression. The distribution constant for both alcohols agree well with those previously obtained using different techniques. Since the best fit below the structural transition correlates as well with the experimental points above the structural transition, it seems that no difference exists in the standard partial molar heat capacities of alcohols in the two shapes of the micelles. Also, from the present data and those for alkanols in sodium dodecylsulfate reported in the literature it seems that the standard heat capacity of alcohols in the micellar phase does not depend on both the alcohol alkyl chain length and the nature of the hydrophilic moiety of the head group of the micelles.     

Volumes of mixtures of alcohols in water at 25°C

Many studies support the idea that alcohols in water undergo microphase transitions which are, in many respects, similar to micellization. To investigate the interactions in these systems even further, the volumes of transfer of normal alcohols of intermediate chain length, kept near infinite dilution, were measured from water to aqueous solutions of 2-propanol and 2-butoxyethanol. These results were compared with the volumes of transfer of the same alcohols to aqueous solutions of octyldimethylamine oxide, a well-characterized non-ionic surfactant. The trends observed are all very similar, exhibiting in many cases a maximum in the transition region. This tends to confirm the formation of mixed aggregates in aqueous mixtures of alcohols, but, in a general way, it is also shown that the magnitude of an extremum in the functions of transfer is related to the relative hydrophobicities of the present solutes, the extremum appearing in most cases only when the transferred solute is more hydrophobic than the main solute.     

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.     

Microheterogeneity in aqueous-organic solutions: Heat capacities,volumes and expansibilities of some alcohols,aminoalcohol and tertiary amines in water

The heat capacities per unit volume and the densities of aqueous solutions of 2-propanol, neopentanol, tert-amylalcohol, 2-amino-2-methylpropanol, triethylamine and diethylmethylamine were measured, in many cases as a function of temperature, over the whole mole fraction or solubility range. Apparent and partial molal heat capacities, volumes and expansibilities were derived. The concentration dependence of these functions suggest the existence of transitions in some of these systems, in the water-rich region, qualitatively similar to micellization. The large relaxation contribution observed with some of the thermodynamic functions of hydrophobic alcohols and amines suggests a reinforcement of hydrophobic hydration due to strong hydrogen-bonding interactions of the polar groups with water.     

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.     

I>D-甘露醇在正丙醇和异丙醇水溶液中的体积性质

使用石英振荡管密度计精确测定了298.15 K温度下不同浓度的甘露醇-正丙醇-水和甘露醇-异丙醇-水三元溶液的密度. 计算了甘露醇的表观摩尔体积V_Φ和极限偏摩尔体积, 得到了其由纯水溶剂转移至混合溶剂中的迁移偏摩尔体积. 结果表明, 正丙醇在溶液中对甘露醇体积性质的影响较异丙醇显著. 从溶质-溶剂分子间相互作用及丙醇同分异构体中羟基位置的不同对体积性质的变化规律进行了讨论.     

Thermal behavior of n-alcohols, benzene, and toluene in water urea and water ethyleneglycol systems

Relations are suggested for calculating the heat characteristics of alcohols, benzene, and toluene in aqueous solutions of urea and ethylene glycol. The solution heat of an alcohol shows greater dependence on the glycol concentration, while the heat capacity of solution, on the urea concentration. For n-butanol in aqueous glycol, the characteristic temperature at which the solution heat of the alcohol is zero decreases as the glycol concentration increases. The dependence of the characteristic temperature of 1-butanol on the urea concentration has a maximum.     

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.     

1H NMR研究溶质浓度对三碳多元醇水溶液氢键作用以及玻璃化的影响

为考察溶质浓度对三碳多元醇水溶液氢键作用以及不同物质玻璃态形成能力的影响,采用¹H NMR外标法研究不同浓度的1-丙醇（NPA）,2-丙醇（IPA）,1,2-丙二醇（PG）,1,3-丙二醇（PD）和丙三醇（glycerol）的水溶液在室温常压下质子化学位移.结果表明:具有CH₃CH（OH）一基团的PG烷基质子的化学位移变化趋势与其他几种醇相比有较大差异.醇羟基质子与水分子的氧形成较强O-H…O氢键.相同摩尔分数下,羟基数的增加导致水质子和羟基质子的化学位移降低,而且羟基位置不同也会导致水质子和羟基质子化学位移差异.这几种三碳多元醇碱性强弱的顺序和降低冰的均相成核温度能力的顺序一致,即glycerol>PG>PD>IPA>NPA,¹H NMR技术表明glycerol和PG更适合用作低温保护剂.     

Thermodynamics of bolaform electrolytes. V. Enthalpies and heat capacities in aqueous urea solutions

The partial molal heats of solution at infinite dilution of 1,4-bis(triethylammonium)butane dibromide and 1,10-bis(triethylammonium)decane dibromide in aqueous urea (up to 8m urea) have been determined calorimetrically in the temperature range 18–33°C. These data have been used to derive the partial molal heat capacities at infinite dilution, the enthalpies of transfer, and heat capacities of transfer at infinite dilution from water to urea-water solutions. The results show that the enthalpies of transfer are negative and decrease with increasing urea concentrations. The heat capacities of transfer are negative at low urea concentrations and increase in magnitude at higher urea concentrations. In the case of the smaller cation the partial molal heat capacity in 8m aqueous urea solution is greater than in pure water. The results are discussed in terms of structural changes in the solvents on dissolution.     

三种氨基酸从水到DMSO水溶液的迁移焓研究

用微量量热法测定甘氨酸、L-丙氨酸、L-丝氨酸在二甲基亚砜(DMSO)水溶液中的溶解焓, 计算得到三种氨基酸从水到DMSO水溶液的迁移焓, 根据共球交盖模型对氨基酸与DMSO在水溶液中的相互作用进行讨论, 并与前期的氨基酸在尿素水溶液体系中的迁移焓进行比较. 结果显示, 氨基酸与共溶剂分子之间产生的静电相互作用以及亲水-亲水相互作用对氨基酸迁移焓有负贡献, 而亲水-疏水、疏水-疏水相互作用对氨基酸迁移焓有正贡献. 与尿素水溶液中氨基酸迁移焓的绝对值随尿素浓度的增加而增加, 并规律性地出现多个变化点的情况不同, 氨基酸从水到DMSO水溶液的迁移焓随DMSO浓度的增加而线性增加. 这种差异反映了尿素与DMSO及其水溶液结构的不同, 为认识尿素在水溶液中的缔合作用提供了对比依据.     

Thermodynamic Properties of Aqueous Glucose–Urea–Salt Systems

In this work, the thermodynamic behavior of aqueous solutions containing the solutes NaCl, glucose, and/or urea is investigated. These substances are vital components for living bodies and further they are main components of blood serum. Osmotic coefficients were determined by cryoscopic measurements in single-solute and multi-solute aqueous solutions containing salts (NaCl, KCl, CaCl₂), glucose, and/or urea. The results show that NaCl determines the osmotic coefficients in the urea/glucose/NaCl/water system. Investigation of the effect of different salts on osmotic coefficients revealed ion-specific effects. At physiologically important solute concentrations in typical blood serum solutions, the osmotic coefficients were found to be in the range of 0.90–0.93. In a second step, the state of water in different glucose/salt/water and urea/salt/water systems was investigated. Depending on the kind of salt, the chemical potential of water in urea/salt/water is either higher or lower than in glucose/salt/water systems at equal nonelectrolyte concentrations. This result was found to be independent of the salt molality. Finally, the investigated systems were modeled with the Pitzer model and the ePC-SAFT equation of state, which allowed predicting of the properties of these multi-solute aqueous solutions.     

A new version of differential flow heat capacity calorimeter; tests of heat loss corrections and heat capacities of aqueous NaCl from T = 300 K to T = 623 K

A new differential flow heat capacity calorimeter was constructed. It is designed to operate at temperatures up to 700 K and pressures up to 35 MPa and its primary use is for determining the massic heat capacities at constant pressure of dilute aqueous solutions. The instrument works in the so-called isoperibol regime, where the fluid sample flowing through the cell is heated by an electrical heater and the power necessary to provide a constant temperature rise is measured relative to that for a reference fluid (water). From the two values of power for sample and water the ratio of massic heat capacities of the sample to that of water can be calculated. A thorough investigation of calibration techniques showed that the calorimetric performance is very sensitive to the thermal conductivities of the sample and reference fluids. Measurements under turbulent flow conditions are questionable since there is no guarantee that by changing the flow rate the experiments and the calibrations would be performed at the same flow conditions. The procedure is very accurate and sensitive when measuring the difference in heat capacity between a solvent and a dilute solution of solute in the same solvent. The calorimeter was used to measure heat capacities of aqueous solutions of NaCl at eight temperatures up to 623 K and pressures to 30 MPa. The newly obtained values show consistency with previously published results and enlarge the database of experimental values aboveT =  573 K, where experimental data are rare.     

Heat capacity of alcohols in aqueous solutions in the temperature range from 5 to 125°C

Using a precise technique of scanning microcalorimetry the heat capacity differences between water and dilute aqueous solutions of ethanol, n-propanol, n-butanol and n-pentanol were measured from 5 to 125°C and the partial molar heat capacities of these substances in water were determined. It was found that the heat capacity increment for alcohol disolved in water is proportional to the number of the-CH ₂ ^– groups and decrease with a temperature increase. The heat capacity increment of hydration of non-polar groups is shown to be positive and large at room temperature and decreases in magnitude as the temperature increases. In contrast, the heat capacity increment of hydration of polar groups is negative at room tempreature and increases as the temperature increases. From the temperature dependence of the heat capacity increment one can assume that the water molecules solvated by the non-polar groups of the alcohols behave in a non-cooperative manner.