Densities and heat capacities of water−substrate, water−cyclodextrin, and water−substrate−cyclodextrin systems were determined at 298 K. The substrates studied are sodium n-alkanecarboxylates (C n COONa) (from sodium acetate to sodium decanoate) and the cyclodextrins are hydroxypropyl-α-cyclodextrin (HP-α-CD), hydroxypropyl-β-cyclodextrin, (HP-β-CD), hydroxypropyl-γ-cyclodextrin (HP-γ-CD) and β-cyclodextrin (β-CD). The apparent molar volumes and heat capacities of C n COONa in water were calculated as functions of concentration. The standard partial molar properties agree with those obtained by using the additivity rule. HP-β-CD essentially does not affect the thermodynamic properties of C1COONa and C2COONa. Contrarily, the formation of the inclusion complex between cyclodextrin and substrate modifies the apparent molar properties. From the standard partial molar properties of the substrate in pure water and in water + HP-β-CD mixtures and literature values for the equilibrium constant for the inclusion complex formation, the standard partial molar properties of the complex ( ) were calculated. The increase of with the number of carbon atoms in the alkyl chain (n) is consistent with the solubilization of methylene groups in the hydrophobic cavity of the cyclodextrin and the expulsion of some water molecules from the cavity. To explain the dependence of on n, conformational effects are also invoked. Studies performed as functions of cyclodextrin concentration evidence that micellization occurs provided that all the cyclodextrin is almost complexed and that the dispersed surfactant concentration equals its critical micelle concentration in water. Data in HP-α-CD, HP-β-CD, HP-γ-CD, and β-CD indicate that the size cavity of the cyclodextrin strongly affects the thermodynamics of the inclusion complex formation while the nature of the hydrophilic shell of the cyclodextrin does not.

Densities and heat capacities of water-substrate and water-substrate-cyclodextrin mixtures were determined at 298 K. The substrates studied are sodium n-perfluoroalkanoates, (CF)nCOONa, (from sodium perfluoroacetate to sodium perfluorooctanoate) and the cyclodextrins are hydroxypropyl-R-cyclodextrin (HP-R-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD), and hydroxypropyl-γ-cyclodextrin (HP-γ-CD). From experimental data of (CF)nCOONa in water, the standard partial molar properties were determined. Moreover, the properties of micellization of the surfactants were determined. HP-β-CD hardly affects the thermodynamic properties of CF3COONa while it strongly does those of the other substrates. From the experimental data the standard partial molar properties of the inclusion complex were calculated and compared to those of the sodium n-alkanoates + HP-β-CD we reported elsewhere (Langmuir 1998, 14, 6045). The larger hydrophobicity of the CF2 group with respect to the CH2 one is reflected in the properties of the inclusion complex. Studies extended to HP-R-CD and HP-γ-CD indicate that the size cavity of the cyclodextrin influences the thermodynamics of the inclusion complex formation more than that for the hydrogenated substrates. The presence of cyclodextrin affects the property of the surfactant in the aqueous phase while it scarcely does that in the micellar phase.

Conductivity, density, heat capacity, enthalpy of dilution, and osmotic coefficient measurements of water−sodium perfluorooctanoate (NaPFO)−sodium dodecanoate systems were carried out as functions of the surfactants' total molality (m t) at different mole fractions (X NaPFO). From conductivity data, the critical micelle concentration (cmc) and the degree of ionization (β) of the micelles were derived. The cmc's of the micelles are higher than those of the pure surfactants while β depends linearly on X NaPFO. At a given mole fraction, the apparent molar volume (V Φ) and heat capacity (C Φ) of the mixture increases and decreases monotonically with m t, respectively. From data in the premicellar region, the standard (infinite dilution) partial molar properties (Y o) of the mixtures were calculated for both volume and heat capacity. Y o depends linearly on X NaPFO according to the ideal behavior. From data in the postmicellar region, the excess properties (Y exc) for the mixed micelles formation from pure micelles were calculated. The values of the excess volumes and heat capacities are positive and negative, respectively, in the whole range of composition. The excess free energy (G exc) is negative while both enthalpy and entropy are positive. On the basis of the pseudophase transition model and experimental evidences, the G exc vs composition profile was derived. This profile indicates the presence of a critical point for 0.4 ≤ X NaPFO ≤ 0.6. According to this approach, G exc was calculated for some mixtures. It turned out that sodium dodecanoate and sodium dodecyl sulfate micelles are miscible in the whole range of composition while ammonium perfluorononanoate (NH4PFN) and ammonium dodecyl sulfate micelles are partially miscible, and the coexistence of the two mixed micelles pseudophases occurs in the range 0.43 ≤ X NH 4 PFN ≤ 0.75. In the case of the sodium decyl sulfate−sodium perfluorooctanoate system, only a critical point is present.

Molar excess volumes V* have been measured as a function of mole fraction at 288.15, 308.15, and 318.15 K for binary liquid systems of the type cyclic ether (x.,) + n -alkane by using pycnometry and, In three cases, vibrating-tube denslmetry (VTD). The cyclic ethers were oxolane (tetrahydrofuran, C4HaO), oxane (tetrahydropyran, CaH10O), 1,3-dioxolane (1,3-C3Ha02), and 1,4-dloxane (1,4-C4H802); the n -alkanes were -decane and n-tetradecane. VE for 1,4-dloxane + n-heptane was determined for 298.15 K only. All excess volumes are positive. Ve(x4 = 0.5) for any mixture containing an mc-membered cyclic dlether Is considerably larger than for the corresponding mixture (i.e., with the same n-alkane) Involving an mc-membered cyclic monoether.For a given ether, VE shows a pronounced Increase with Increasing chain length of the n -alkane.

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