A. Inglese

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.

Excess molar heat capacities of (1,4-dioxane+ an n-alkane): an unusual composition dependence

Abstract Excess molar heat capacities C p ,m E at constant pressure were measured, as a function of mole fraction x at 298.15 K and atmospheric pressure, for { x 1,4-C 4 H 8 O 2 + (1− x )C n H 2 n +2 } for n = 7, 10, and 14. The instrument used was a Picker flow calorimeter. The composition dependence of C p ,m E of these three mixtures is strikingly unusual in that two minima are observed in each case, the more prominent being situated at small values of x : x ′ min = 0.185 for n = 7; x ′ min = 0.251 for n = 10; and x ′ min = 0.289 for n = 14. With increasing chain length the corresponding excess molar heat capacities become more negative: C p ,m E ( x ′ min )/(J·K −1 ·mol −1 ) is, respectively, −0.95, −1.53, and −2.53. The less prominent minima are located around x ″ min = 0.9, with C p ,m E ( x ″ min )/(J·K −1 ·mol −1 ) being −0.40 for n = 7, −0.54 for n = 10, and −0.63 for n = 14. The mole fractions x max of the maxima of the three curves and the corresponding values of C p ,m E ( x max )/J·K −1 ·mol −1 ) are 0.605, 0.03; 0.699, 0.03; 0.780, 0.22.

Excess volumes and excess heat capacities of oxane + cyclohexane and 1,4-dioxane + cyclohexane

Abstract Molar excess volumes VE at 298.15 K have been determined as a function of mole fraction x for the two binary liquid systems oxane (tetrahydropyran, C5H10O) + cyclohexane(c-C6H12) and 1,4-dioxane(1,4-C4H8O2) + cyclohexane by vibrating-tube densimetry. In addition, a Picker flow calorimeter was used to obtain molar excess heat capacities CPE at constant pressure at the same temperature. VE is positive for both systems and rather symmetric, with VE(x1 = 0.5) amounting to 0.317 cm3 mol−1 for &[;x1(C5H10O)+x2(c-C6H12)&];, and to 0.961 cm3 mol−1 for &[;x1(1,4-C4H8O2)+x2(c-C6H12)&];. For the former system, CPE is negative and noticeably skewed toward the cyclohexane side. The composition dependence of CPE for the latter system is rather unusual in that two minima are observed, the more pronounced being situated at x′1,min = 0.173, with CPE(x′1,min) = −0.97 J K−1 mol−1. The second minimum is rather shallow and is located at x″1,min = 0.761, with CPE(x″1,min) = −0.56 J K−1 mol−1. The maximum of the curve is at x1,max = 0.539, with CPE(x1,max) = −0.47 J K−1 mol−1.

Thermodynamics of binary mixtures containing cyclic ethers 3. Excess enthalpies of oxolane, 1,3-dioxolane, oxane, and 1,3-dioxane + benzene and + tetrachloromethane

Abstract The molar excess enthalpy H E has been measured as a function of mole fraction x at atmospheric pressure and 298.15 K for each of the six binary liquid mixtures: benzene + oxolane, and + 1,3-dioxolane, and tetrachloromethane + oxolane, + 1,3-dioxolane, + oxane, and + 1,3-dioxane. The overall consistency of the flow-calorimetric measurements is characterized by standard deviations from Redlich-Kister type smoothing equations which do not exceed ±1 per cent of the extreme value of H E . The mixtures with cyclic monoethers exhibit relatively large negative excess enthalpies, e.g. for (oxolane + tetrachloromethane) H E = −788.0 J mol −1 at x = 0.5. Mixtures containing cyclic diethers show rather small positive or negative excess enthalpies, e.g. for (1,3-dioxolane + tetrachloromethane), H E = 146.3 J mol −1 at x = 0.5, and for (1,3-dioxane + tetrachloromethane), H E = − 119.0 J mol −1 . The latter mixture shows S-shaped dependence of H E on x with the very small positive section located at small mole fractions of cyclic ether.

Enthalpies of solution and dilution of butanol and pentanol in dodecyltrimethylammonium bromide micellar solutions

The enthalpies of solution and of dilution of 1-butanol and 1-pentanol were measured in micellar solutions of dodecyltrimethylammonium bromide by systematically changing the concentration of alcohols and surfactant. The enthalpies of solution at infinite dilution of alcohols at each surfactant concentration were evaluated from a linear plot. This quantity increases with surfactant concentration (up to 0.8m) with a curvature which depends on the alcohol alkyl chain length. The difficulties arising for a quantitative treatment of both the enthalpies of dilution and of solution at finite alcohol concentrations are discussed. The dependence on the surfactant concentration of the standard enthalpies of solution and the enthalpies of dilution for m→0 are rationalized. From the resulting equations the distribution constant, standard enthalpy of transfer, standard enthalpy of solution, and the alcohol-alcohol interaction parameter in the micellar phase are evaluated. The enthalpies of transfer obtained using this technique agree well with those previously reported from enthalpies of mixing. The distribution constants also agree with those reported in the literature from several approaches: mixing enthalpies, partial molar volumes, and the dependence of the cmc on added alcohol.

Excess enthalpy, excess heat capacity and excess volume of 1,2,4-trimethylbenzene+, and 1-methylnaphthalene+ an n-alkane

Abstract A flow microcalorimeter of the Picker design was used to measure excess molar enthalpies HE at 298.15 K as a function of mole fraction χ1 for several mixtures belonging to series I: {χ11,2,4-C6H3(CH3)3 + χ2n-ClH2l+2}, and series II: {χ11-C10H7CH3 + χ2n-ClH2l+2}. The chain length l of the n-alkanes ranged between 7 and 16. 1,2,4-trimethylbenzene and 1-methylnaphthalene have about the same size and shape as the previously investigated chloro derivatives 1,2,4-C6H3Cl3 and 1-C10H7Cl but a much smaller reduced dipole moment. The calorimeter was used in the discontinuous mode. A plot of HEmax (i.e., the maximum value of HE with respect to composition) against l for series I shows a shallow minimum around l = 11 with HEmax (l = 11) ≈ 250 J mol−1, whereas HEmax for series II decreases over the whole range 7 ⩽ l ⩽ 16: HEmax (l = 7) ≈ 760 J mol−1, and HEmax (l = 16) ≈ 595 J mol−1. The corresponding enthalpic interaction parameters h12, calculated from zeroth-order KGB (Kehiaian-Guggenheim-Barker) theory, decrease with increasing l, and the rate of decrease, dh12/dl, diminishes for larger chain lengths. For three mixtures belonging to series I (l = 7, 10, 14), excess molar volumes VE and excess molar heat capacities CEP at constant pressure were mesured at the same temperature. VE was determined with a vibrating-tube densimeter (flow conditions), and CEP was obtained with another type of flow calorimeter (stepwise procedure). VE(χ1 = 0.5)/(cm3 mol−1) = −0.207 for l = 7, 0.060 for l = 10, and 0.145 for l = 14. The corresponding values for CEP x1 = 0.5)/(J K−1 mol−2) are 0.32, 0.66 and −0.09. Thus the chain length dependence of the excess molar heat capacity is qualitatively similar to that observed for the series with the homomorphic chloro derivative, (1,2,4-C6H3Cl3 + n-ClH2l+2), and to that of (1-C10H7Cl+n-ClH2l+2).

Thermodynamics of binary mixtures containing cyclic ethers 5. Excess enthalpies of 1,3-dioxolane +, and 1,4-dioxane + alkanoic acid (HCO2H to C7H15CO2H)

Abstract The molar excess enthalpy H m E has been determined as a function of mole fraction x at atmospheric pressure and 298.15 K for 12 binary liquid mixtures formed from 1,3-dioxolane +, and 1,4-dioxane + formic acid, + acetic acid, + propionic acid, + butyric acid, + hexanoic acid (caproic acid), and + octanoic acid (caprylic acid). The mixtures (1,3-dioxolane + formic acid), (1,4-dioxane + formic acid), and (1,4-dioxane + acetic acid) show negative excess enthalpies. All the others show positive excess enthalpies which increase with increasing chain length n of the alkanoic acid C n H 2n + 1 CO 2 H. For n = 0, H m E ( x = 0.5) of ( 1 2 1,3- C 3 H 6 O 2 + 1 2 C n H 2n + 1 CO 2 H ) is about 750 J·mol −1 less negative than of ( 1 2 1,4- C 4 H 8 O 2 + 1 2 C n H 2n + 1 CO 2 H ); for all other n , H m E ( x = 0.5) of the mixtures with 1 2 1,3- C 3 H 6 O 2 is about 320 to 450 J·mol −1 more positive than for the corresponding mixtures with 1 2 1,4- C 4 H 8 O 2 , with no pronounced dependence on n . This is in contrast to the situation found for (a cyclic monoether + a carboxylic acid), (4) where the corresponding increments between mixtures containing the same acid and either a five-membered or a six-membered cyclic monoether have opposite signs.

Molar excess volumes and excess heat capacities of (1,2,4-trichlorobenzene + an n-alkane)

Abstract Molar excess volumes V m E at 298.15 K were obtained, as a function of mole fraction x for the four binary liquids 1,2,4-trichlorobenzene + n -hexane, + n -nonane, + n -decane, and + n -tetradecane from measurements of the density with a vibrating-tube densimeter. In addition, a Picker flow calorimeter was used to determine molar excess heat capacities C p .m E at constant pressure at 298.15 K for three of these mixtures: 1,2,4-trichlorobenzene + n -hexane, + n -nonane, and + n -decane. V m E for { x 1,2,4-C 6 H 3 Cl 3 + (1 − x )C 6 H 14 ) is negative and rather large (at x = 0.5, V m E = −0.941 cm 3 ·mol −1 ), and becomes more positive with increasing chain length n of the alkane C n H 2 n + 2 . For example, for ( x 1,2,4-C 6 H 3 Cl 3 + (1 − x )C 14 H 30 ) we observe V m E = 0.103 cm 3 ·mol −1 at x = 0.5. The C p. m E s are all negative. For the range of n considered (6 ⩽ n ⩽ 10), the absolute value | C p .m E | decreases with increasing n .

Volumes and heat capacities of binary liquid mixtures of water—sulfolane and water—hexamethylphosphotriamide

Abstract Density and heat capacity measurements of water—sulfolane mixtures at 303.15 K and water—hexamethylphosphotriamide mixtures at 298.15 K have been performed over the whole composition range. Molar, excess, apparent molar volumes and heat capacities were calculated for the two systems. The trends of these functions are discussed in terms of specific interactions between the components of the solvent mixtures and the changes caused by the organic solvents on the water structure.

A phase‐locked loop for driving vibrating tube densimeters

A phase‐locked loop has been developed for use in driving vibrating tube densimeters. This circuit allows reliable density measurements under high‐noise conditions with lower drive power to the vibrating tube. The design and operation of the instrument is discussed.