Interactions of poly(amidoamine)dendrimers having surface carboxyl groups with cationic surfactants

Interactions between poly(amidoamine)dendrimers with surface carboxyl groups and cationic surfactants in aqueous solutions were investigated by surface tension, fluorescence spectra, and dynamic scattering measurements. The dendrimers used were three generations (G1.5, 3.5, and 5.5) and two cationic surfactants were dodecyltrimethylammonium bromide (DTAB) and 1,2-bis(dodecyldimethylammonio)ethane dibromide (2RenQ). Under a constant concentration of surface groups of the dendrimers, the results of surface tension and fluorescence spectra measurements indicate that aggregates between DTAB and the dendrimers are formed at lower DTAB concentration than that of DTAB alone, whereas those between 2RenQ and the dendrimers are formed at higher 2RenQ concentration than that of 2RenQ alone. In addition, the aggregates show higher surface activity when the generation decreases from 5.5 to 1.5. Hydrodynamic radius obtained from dynamic scattering measurement suggests that the aggregates are formed by adsorbing surfactant on the surface of the dendrimers, not by bridging the dendrimers through the surfactant.