- Thermodynamic Properties of N-octyl-, N-decyl- and N-dodecylpyridinium Chlorides in Water
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Densities, heat capacities and enthalpies of dilution at 25 deg C and osmotic coefficients at 37 deg C were measured for N-octyl-, N-decyl- and N-dodecylpyridinium chlorides in water over a wide concentration region.Conductivity measurements were performed in order to evaluate the cmc and the degree of counterion dissociation.Partial molar volumes, heat capacities, relative enthalpies and nonideal free energies and entropies at 25 deg C were derived from the experimental data as functions of the surfactant concentration.The changes with concentration of these properties are quite regular with the exception of the heat capacities which display anomalies at about 0.9, 0.25 and 0.12 mol-kg-1 for the octyl, decyl and dodecyl compounds, respectively.At these concentrations there were also changes in the slopes of the specific conductivity and of the product of the osmotic coefficients and the molality vs. concentration.These pecularities can be ascribed to micelle structural transitions.The thermodynamic functions of micellization were graphically evaluated on the basis of the pseudo-phase transition model.These data have been compared to those for alkyltrimethylammonium bromides and alkylnicotinamide chlorides.It is shown that the introduction of the hydrophilic CONH2 group lowers the hydrophilic character of the pyridinium ring. KEY WORDS: N-octylpyridinium chloride; N-decylpyridinium chloride; N-dodecylpyridinium chloride; densities; heat capacities; enthalpies of dilution; osmotic coefficients; activity coefficients; partial molar volumes; partial molar heat capacities; partial molar relative enthalpies; nonideal free energies; nonideal entropies; thermodynamics of micellization
- Causi, S.,Lisi, R. De,Milioto, S.
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- Binding of N-Alkylpyridinium Chlorides to Nonionic Micelles
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Binding of N-alkylpyridinium chlorides (C10, C12, and C14) to dodecyl oxyethylene ether (C12E6 and C12E8) micelles is determined in the presence of 5 mol m-3 NaCl at various temperatures by potentiometry which employs an electrode responsive to the surfactants.Binding affinity is expressed in terms of a distribution coefficient, Kx, of a cationic surfactant between the aqueous bulk phase and the nonionic micellar phase, and is larger for an alkylpyridinium cation with a longer hydrocarbon chain.The values of Kx are divided into three regions depending on the mole fraction of bound cationic surfactant in a micelle, X.At X x remains constant, while for 0.02 0.2.The constant Kx values reflect an intrinsic binding affinity (K0).With increase in X, electrostatic repulsion among bound cationic surfactants causes decreased Kx values, which may be analyzed by a simple electrostatic theory to estimate the position of bound cationic head groups.From the temperature dependence of K0, it is found that the binding process is nearly athermal for C12E8 micelles but exothermic for C12E6 micelles, the latter associated with the growth of micellar size with temperature.
- Shirahama, Keishiro,Nishiyama, Yoshinori,Takisawa, Noboru
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p. 5928 - 5930
(2007/10/02)
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