A microcalorimetric titration study on the micelle formation of alkanediyl-α,ω-bis(dimethylalkylammonium bromide) surfactants at a 283.15–343.15 K temperature range

The aim of this study was to investigate the self-assembly process for m-8-m gemini surfactants, for m = 8 and 12, in water, using the microcalorimetric titration method within the temperature range of 283.15–343.15 K. The enthalpy of micellization (∆Hmic) and critical micelle concentration (c.m.c.) have been calculated by using modified sigmoidal Boltzmann equation. Other thermodynamic parameters ∆Gmic, ∆Smic, and ∆Cp,mic, associated with micellization process were determined on the basis of the calorimetric results by applying the pseudo-phase separation model. The c.m.c. and ∆Hmic values strongly depend on the temperature and the alkyl chain length. The enthalpy of micellization decreases and then changes its sign and becomes negative when temperature increases. The temperature dependence of the c.m.c. for the surfactants investigated exhibits typical U-shape. The results obtained are compared with literature data for other gemini cationic surfactants with a different alkyl chain length. The differences are analyzed in terms of differences in the hydrophobic interactions between the hydrocarbon chains.