Physicochemical properties of quaternized poly(amidoamine) dendrimers with four octyl chains

A cationic dendrimer-type tetrameric surfactant (C(8)qbG0) with four octyl chains and four ammonium groups was synthesized by the reaction of poly(amidoamine) dendrimers with generation of zero and glycidyldimethyloctylammonium bromide. The physicochemical properties of C(8)qbG0 and of their mixtures with sodium dodecyl sulfate (SDS) were characterized by investigating surface tension, electrical conductivity, fluorescence of pyrene, and dynamic light-scattering. The critical micelle concentration (cmc) of C(8)qbG0 was 13 mmol dm(-3) at the concentration of one terminal group and the surface tension at the cmc attained 34 mN m(-1). The occupied area of C(8)qbG0 was 1.94 nm(2) molecule(-1), indicating that the tetrameric dendrimers adsorb widely at the air/water interface. The fluorescence intensity ratio of the first-to-third band in the emission spectra of pyrene for C(8)qbG0 decreased from around the cmc obtained by the surface tension measurement. The hydrodynamic radius of C(8)qbG0 determined by dynamic light-scattering was about 1.3 nm. The addition of SDS to the aqueous solutions of C(8)qbG0 enhanced the surface activities; the mixtures exhibited lower cmc, lower surface tension, and higher solubilization of pyrene than SDS alone. It was found that the mixtures of C(8)qbG0 and SDS form large aggregates due to the interactions between their alkyl chains as well as hydrophilic groups.