The pre-modification of surfactant counterions using transition metal salts provides a means to activate the interface using corresponding properties of metal ions. In this work, a cationic surfactant cetyltrimethylammonium bromide (CTAB) was modified by pre-mixing metal chlorides (FeCl3, CuCl2 and ZnCl2) and CTAB in 1:1 molar ratio using methanol as solvent. As a result, FeCl3, CuCl2 and ZnCl2 were added as [FeCl3Br]-1, [CuCl2Br]-1 and [ZnCl2Br]-1 respectively acting as counter anions (CAs) instead of bromide anion. Hence CTAB was called CTAF, CTAC and CTAZ in order of added CAs i.e., [FeCl3Br]-1, [CuCl2Br]-1 and [ZnCl2Br]-1 respectively. The effect of these metal chlorides on the micellar behaviour of CTAB was investigated using conductivities of their different solutions. Furthermore, the critical micelle concentration (CMC) as well as the degree of counterion binding were considered at 25.0, 30.0, 35.0, 40.0 and 45.0 °C 0.1 °C. The analysis of results revealed that incorporation of metal cations reduces the CMC values in the order CTAF CTAZ CTAC CTAB. Change in entropy (S), enthalpy (H) and free energy (G) were calculated to understand the thermodynamics of micellization under the circumstances. The aim of this study is to improve the understanding regarding the presence of transition metals in micellization process as well as the possibility of their interactions with Bromide counterions and possibility of the formation of complex counter-anions.

Sumbal Saeed, Arif Hussain, M. Faizan Nazar, Hameed Ullah, Afzal Shah, Syed Sakhawat Shah and Asad Muhammad Khan