Properties of binary surfactant systems of nonionic surfactants C12E10, C12E23, and C12E42 with a cationic gemini surfactant in aqueous solutions

Properties of binary surfactant systems of nonionic surfactants poly(ethylene oxide) (PEO) lauryl ethers (C12E10, C12E23, C12E42) with a cationic gemini surfactant, butanediyl-α,ω-bis(tetradecyldimethylammonium bromide) (14-4-14), have been investigated by Steady-state Fluorescence (FL), zeta potential, Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM), Cryogenic Transmission Electron Microscopy (CryoTEM), and X-ray Diffraction (XRD). Through FL measurements, critical micelle concentration (CMC) of the three binary systems for different mixing mole fractions is determined and the values fall between those of pure constituent surfactants. Ideal CMC (CMCideal), mole fraction in aggregates (X), interaction parameter (β), activity coefficients (f1 and f2), and excess free energy of mixing (ΔGex) have been calculated. All these parameters indicate nonideal behavior and synergistic interactions between the constituent surfactants, which is explained in terms of electrostatic attraction between headgroups of constituent surfactants and reduction of electrostatic repulsion between headgroups of 14-4-14 due to the presence of nonionic surfactants. DLS, TEM and CryoTEM results show that nonionic surfactants facilitate the formation of larger aggregates. Micelles and vesicles in larger size compared with those of 14-4-14 coexist in the mixed solutions. Both surfactant composition and PEO chain length are found to play a strong effect on the properties of the binary systems.

Cryogenic Transmission Electron Microscopy image of micelles and vesicles formed by binary surfactant system of nonionic surfactant and cationic gemini surfactant.Figure optionsDownload high-quality image (63 K)Download as PowerPoint slideResearch highlights
► The aggregation properties of three binary surfactant systems were investigated.
► The presence of nonionic surfactants has an effect on CMC and aggregate morphology.
► There are strong synergistic interactions between the constituent surfactant.
► Surfactant composition and PEO chain length affect the aggregation properties.
► The work contributes to understand the aggregation behavior and the mixing effect.