Thermodynamics of micellization of cationic surfactants based on dye-surfactant mixed micellar system

A thermodynamic study on the micellization process of two cationic surfactants, viz. the tetradecyltrimethylammonium bromide (TTAB) and Cetyltrimethylammonium bromide (CTAB) are reported with emphasis on the effect of the Acid Green 25 (AG25) dye. The solution behavior of the mixture of surfactant and AG25 dye has been determined using conductivity method. A strong interaction between the dye and both two surfactant is indicated from the above measurements. The critical micelle concentration (CMC) of TTAB and CTAB are found to decrease with increase in the amount of AG25 in the mixture. In order to explain the effect of the dye nature in the micellization process, thermodynamic parameters to include the standard free energy ( D om G ), enthalpy ( D om H ), entropy ( D om S ), of micellization have been discussed. These parameters are evaluated from the variation of the critical micelle concentration (CMC) with temperature by fitting these values to expressions derived on the basis of a micellization thermodynamic model. For both surfactant, the free energy of micellization is weakly temperature dependent and becomes more negative with increasing the size of alkyl chain a more favored micellization. The enthalpy and entropy of micellization decrease strongly with increasing of temperature..

کلیدواژه ها:

Acid Green 25 ، TTAB ، CTAB ، Thermodynamics ، Gibbs energy