Specific conductivities, densities, heat capacities and enthalpies of dilution at (298 \mathrm{~K}) and osmotic coefficients at (310 \mathrm{~K}) were measured for (N, N, N)-octylbutyldimethylammonium, (N, N, N)-octylpentyldimethylammonium, and (N, N)-dioctyldimethylammonium chlorides in water as functions of concentration. From the specific conductivity data, the CMC and the degree of the counterion dissociation have been calculated. It is shown that additional (\mathrm{CH}{2}) groups in the variable alkyl chain affect both CMC and (\beta) less than they do in the single chain surfactants. The partial molar volumes, heat capacities, relative enthalpies, nonideal free energies, and entropies at (298 \mathrm{~K}) were derived as functions of the surfactant concentration. By increasing the tail of the variable alkyl chain, the apparent molar volume and heat capacity vs concentration curves are shifted regularly towards larger and smaller values, respectively. As well, in the micellar region, by increasing the alkyl chain length while the nonideal entropy vs (\log m / C M C) curves are shifted regularly towards more positive values, those for free energy and enthalpy are not. The standard partial molar volumes and heat capacities lincarly increase with the alkyl chain length slopes being slightly larger and smaller, respectively, than those for single chain surfactants. The partial molar volumes and heat capacities in the micellized form are also linearly related to the number of methylene groups with (\mathrm{CH}{2}) contributions which are close and larger, respectively, than those for single chain surfactants. However, the heat capacity for the longer homologues deviates from the linearity. Since this peculiarity has been observed for most of the investigated properties, it has been ascribed to a different location of this chain in the micellar structure with respect to the shorter chains. In addition, thermodynamic properties of (N, N, N)-octylbutyldimethylammonium chloride are compared with those of (\mathrm{N}, \mathrm{N})-octylmethylpiperidinium chloride which can be considered to be derived from the fusion of a methyl and the butyl groups in the (N, N, N)-octylbutyldimethylammonium chloride. (c) 1993 Academic Press, Inc.