Abstract
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 (∆H mic) and critical micelle concentration (c.m.c.) have been calculated by using modified sigmoidal Boltzmann equation. Other thermodynamic parameters ∆G mic, ∆S mic, and ∆C p,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 ∆H mic 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.
Highlights
As the name implies, gemini surfactants of general formula m-s-m, consist of two surfactant moieties with alkyl chain-mH
The aim of this study was to investigate the selfassembly 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
In this study we examined the thermodynamics of micellization process of aqueous solutions of alkylene-a,x-bis(dimethylalkylammonium bromides) with the general formula: m-8-m for m = 8, 12 within the temperature range of 283.15–343.15 K using the isothermal titration microcalorimetry (ITC)
Summary
Gemini surfactants of general formula m-s-m, consist of two surfactant moieties with alkyl chain-m. Łudzik together with appropriate literature data concerning other gemini surfactants would make it possible to analyze the effect of the alkyl chain length as well as that of temperature change on the value of enthalpy of micellization and on the c.m.c value of the systems under question. Octylene-1,8-bis(dimethyloctylammonium bromide) was synthesized as it was described in our earlier paper [20]. Octylene-1,8-bis(dimethyldodecylammonium bromide), (surfactant 12-8-12) was carried out according to procedure given by Zana [21] for the preparation of surfactants but methanol was used as solvent. The obtained crude product was purified by crystallization from ethyl acetate/propan-2ol (95/5) mixture (m.p. 202–204 °C, yield 58%)
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