Concentration-dependent physicochemical behaviors and micellar interactions in polyalkoxylated fatty alcohol-based binary surfactant systems

Abstract

The concentration-dependent physicochemical behaviors of the binary mixtures of polyalkoxylated fatty alcohol (PAFA)-AS (alkyl sulfonate), PAFA-CB (cocamidopropyl betaine) and PAFA-APG (alkyl polyglucosides) and their micellar interactions were determined at the ratios of 9:1, 8:2, 7:3 and 6:4 (w/w). At concentrated level, the rheological study of all the PAFA-mixed surfactants display a Newtonian behavior at low viscosities. Prominent discrepancies among the mixed surfactant systems were observed after stepwise dilution of the samples. In tensiometry study, the types of mutual interaction in the mixed surfactant systems were evaluated by regular solution theory (RST). The CMCexp curves of PAFA-AS and PAFA-CB systems demonstrate lower position than their CMCtheo curves signifying that these nonionic–anionic and nonionic–zwitterionic samples behave nonideal showing synergistic interaction between individual components in the mixed micelles, as further verified by the negative values of interaction parameter β and activity coefficients f1 and f2 are less than 1. Meanwhile, the PAFA-APG system shows no significant mutual interaction between the nonionic–nonionic components in the mixed micelles. TEM micrographs depict the formations of branched wormlike micelles and multiconnected threadlike networks for the PAFA-AS and PAFA-CB systems, respectively, while gigantic multilamellar vesicles for the PAFA-APG system. Upon dilution of these mixed surfactants to CMC, the mixed micelles are in monodisperse sizes of less than 15 nm and in various magnitudes of zeta potential ranging from –2.92 to –21.87 mV.