Mixed Micellization Behavior of m-2-m Gemini Surfactants with Some Conventional Surfactants at Different Temperatures

Abstract

Mixed micellization behavior of dimeric cationic surfactants ethanediyl-1,2-bis(dimethyl alkyl ammonium bromide) (m-2-m where m = 10, 12) with conventional single chain cationic surfactants like cetyltrimethyl ammonium bromide (CTAB), cetylpyridinium chloride (CPC), tetradecyl dimethyl benzyl ammonium chloride (C14BCl) and cetyl dimethyl benzyl ammonium chloride (C16BCl) were studied in aqueous and aqueous polyethylene glycol (PEG) solutions at 298.15, 308.15 and 318.15 K respectively using conductometric and viscometric methods. In aqueous solutions, all the combinations (except 12-2-12 + CTAB) were found to behave nonideally with mutual synergism which decreases with increase in temperature. Various thermodynamic parameters of micellization like ${{\Updelta}}G_{\text{m}}^{\text{o}}$, ${{\Updelta}}H_{\text{m}}^{\text{o}}$ and ${{\Updelta}}S_{\text{m}}^{\text{o}}$ were evaluated and discussed. Similarly in presence of PEG, the thermodynamic properties like ${{\Updelta}}G_{\text{t}}^{\text{o}}$, ${{\Updelta}}H_{\text{t}}^{\text{o}}$ and ${{\Updelta}}S_{\text{t}}^{\text{o}}$ associated with the transfer of surfactant monomers from the medium consisting of polymer-free mixed micelles to polymer-bound mixed micelles at various temperatures were also calculated. The negative values of ${{\Updelta}}H_{\text{t}}^{\text{o}}$ show that aggregation process is more exothermic than micellization whereas the negative values of ${{\Updelta}}S_{\text{t}}^{\text{o}}$ indicate that the presence of polymer bound mixed micelles decreases the degree of randomness of the system. Viscosity studies show that in aqueous solutions all the combinations of 10-2-10/12-2-12 display negative departure in the relative viscosity (η_r) from additivity rule which decreases with increase in temperature. Similarly in the presence of 5% PEG solutions the magnitude of the negative departure decreases for all the combinations and becomes positive in the case of C14BCl and CPC combinations with the studied gemini surfactants at higher temperatures.