Thermodynamic properties of some N-alkyl-N-methylpiperidinium chlorides and N-alkylpiperidine hydrochlorides in water |
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Authors: | S. Milioto S. Causi R. De Lisi |
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Affiliation: | (1) Dipartimento di Chimica Fisica, Università di Palermo, via Archirafi 26, 90123 Palermo, Italy |
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Abstract: | Densities and heat capacities at 25°C were measured for N-octyl-, N-decyl- and N-dodecyl-N-methylpiperidinium chlorides and for N-octyl- and N-dodecylpiperidine hydrochlorides in water as functions of concentration. Enthalpies of dilution at 25°C and osmotic coefficients at 37°C of the N-methyl-N-alkylpiperidinium chlorides were also measured as functions of concentration. The partial molar volumes, heat capacities, relative enthalpies, nonideal Gibbs energies and entropies at 25°C were derived as functions of the surfactant concentration. By increasing the alkyl chain length of the surfactant, both the apparent molar volume vs. concentration curves are shifted toward greater values while the corresponding ones for the heat capacity are moved toward more negative values. These results are consistent with the higher hydrophobicity the longer the alkyl chain of the surfactant is. In the micellar region, the entropy and enthalpy vs. log m/mcmc curves increase in a parallel manner by decreasing the alkyl chain length of the surfactant. Consequently, the negligible effect of the hydrophobicity of the surfactant on the Gibbs energy vs. log m/mcmc trends is due to the enthalpy-entropy compensative effect. The thermodynamic functions of micellization were graphically evaluated on the basis of the pseudo-phase transition model. The absolute values of both the volume and heat capacity of micellization increase with an increasing number of carbon atoms in the alkyl chain (nc). The enthalpy and entropy of micellization vs. nc are convex curves. Comparisons are also made between the present data and those of some alkylpyridinium chlorides reported elsewhere. |
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Keywords: | N-octyl-, N-decyl- and N-dodecyl-N-methylpiperidinium chloride N-octyl- and N-dodecylpiperidine hydrochloride heat capacities enthalpies of dilution osmotic coefficients activity coefficients partial molar volumes, heat capacities and relative enthalpies nonideal Gibbs energies and entropies thermodynamics of micellization |
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