Solvent influence on the mixed micellization behavior of tailored ionic surfactants

Abstract The micellization behavior of mixed micellar systems containing cetyldiethylethanolammonium bromide (CDEEAB) and cetyltriphenylphosphonium bromide (CTPB) surfactants with 10 % (v/v) and 20 % (v/v) solvents i.e. dimethyl sulfoxide (DMSO) and dimethylformamide (DMF) were investigated using conductivity and surface tension measurements at 300 K. Critical micelle concentration (CMC) values increases with increasing mole fraction of CDEEAB. The interfacial properties, Γ max (maximum surface excess), Α min (minimum surface area per molecule) and π CMC (surface pressure at the CMC) have been determined. The Clint equation, Rosen and Rubingh models have been used to calculate interaction parameters ( β m and β σ ). The findings show that protonic solvents change the physicochemical characteristics of the cationic surfactants and significantly improve synergistic interactions. Interestingly, the addition of DMSO (10–20 % v/v) causes a significant increase in the CMC of the CDEEAB + CTPB mixed system. This effect is more noticeable than that of DMF, demonstrating the solvent-dependent modulation of mixed micelle formation. Thermodynamic parameters, <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:mrow> <m:msubsup> <m:mrow> <m:mo>Δ</m:mo> <m:mi mathvariant="normal">G</m:mi> </m:mrow> <m:mrow> <m:mi>a</m:mi> <m:mi>d</m:mi> <m:mi>s</m:mi> </m:mrow> <m:mi>o</m:mi> </m:msubsup> </m:mrow> </m:math> ${\Delta \mathrm{G}}_{ads}^{o}$ , <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:mrow> <m:msubsup> <m:mrow> <m:mo>Δ</m:mo> <m:mi mathvariant="normal">G</m:mi> </m:mrow> <m:mrow> <m:mi>e</m:mi> <m:mi>x</m:mi> </m:mrow> <m:mi>o</m:mi> </m:msubsup> </m:mrow> </m:math> ${\Delta \mathrm{G}}_{ex}^{o}$ , <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:mrow> <m:msubsup> <m:mrow> <m:mo>Δ</m:mo> <m:mi mathvariant="normal">G</m:mi> </m:mrow> <m:mrow> <m:mi>m</m:mi> <m:mtext> </m:mtext> </m:mrow> <m:mrow> <m:mi>o</m:mi> <m:mtext> </m:mtext> </m:mrow> </m:msubsup> </m:mrow> </m:math> ${\Delta \mathrm{G}}_{m\hspace{0.17em}}^{o\hspace{0.17em}}$ values are negative indicating the stability and spontaneity of the mixed micelle.