A temperature study was performed on micelle formation of a series of homologous cationic surfactants having organic counterions (aikanesulfonates) with carbon numbers ranging from 1 to 4: dodecylammonium salts of methanesulfonate (DAMS), ethanesulfonate (DAES), propanesulfonate (DAPS), and butanesulfonate (DABS) in water. The critical micelle concentrations (CMCs) and the degree of counterion binding ( (\beta) ) were determined at different temperatures ranging from 5 to (50^{\circ} \mathrm{C}) by means of conventional electric conductance measurements. From the temperature dependence of (\beta) as well as CMC, Gibbs energy (\Delta G_{m}^{0}), enthalpy (\Delta H_{m}^{0}), and entropy (\Delta S_{m}^{0}), on micelle formation, were estimated for the respective surfactants. As for the temperature dependence of CMC for these surfactants, the temperature-CMC curves have a minimum around (30^{\circ} \mathrm{C}) and show that the CMC at each temperature is lowered by about 3 (\mathrm{mmol} \mathrm{\textrm {dm } ^ { - 3 }}) per methylene group in the alkyl chain of the counterions. The relationship between (\beta) and temperature suggested that the counterion of (\mathrm{MS}^{-})behaves most similarly to common univalent ions such as halide ions. In contrast, (\mathrm{PS}^{-})and (\mathrm{BS}^{-}), having a stronger ability to lower CMC and to promote association of surfactant ions with counterions as well as of surfactant ions themselves, behave more like those of surfactant ions, and (\mathrm{ES}^{-})shows the most complicated character between those of common univalent ions and organic ions. However, the temperature dependence of enthalpy change, (\Delta H_{m}^{0}) demonstrates that these four surfactants are divided into two groups: (1) DAMS and DAES and (2) DAPS and DABS. In addition, the entropy change (\Delta S_{m}^{0}) as a function of alkyl chain length gives evidence that the contribution of the entropy term to the Gibbs energy on micelle formation clearly separates between DAES ( (m=2) ) and DAPS ((m=3)). A similar discontinuity is found even in the plot of (\Delta G_{m}^{0}) versus carbon atom number of alkyl chain, (m), and in the plot of (\Delta G_{m}^{0}) versus estimated hydrodynamic radius of counterions. All the results obtained have indicated that lengthening the alkyl chains initially hinders micelle formation, but the longer chains are markedly effective in lowering the CMC and probably in increasing the aggregation number, owing to enhanced hydrophobic interaction between counterion and the micellar surface and/or core. 1995 Academic Press, Inc.