Adsorption of Poly (amidoamine) dendrimers with Surface Amino Groups and Cationic Surfactants at the Silica/Water Interface

Abstract

Adsorption of poly (amidoamine) dendrimer with surface amino groups and cationic surfactants on silica was studied at pH5. Two dendrimers used were generations of zero and five (G0 and G5). Two cationic surfactants were dodecyltrimethylammonium bromide (DTAB) and 1, 2-bis (dodecyldimethylammonio) ethane dibromide (2RenQ). Adsorption of the dendrimers of GO and G5 increased linearly with the dendrimer concentration, while typical adsorption isotherms were obtained for DTAB and 2RenQ. The adsorption of the dendrimers increased the ζpotential of silica from negative to positive. In a simultaneous adsorption of the dendrimer and cationic surfactant at a fixed concentration of the dendrimer, a competitive adsorption between the dendrimer and surfactant was observed, with the G5 competing more strongly than the GO with the surfactant. Further, a comparison between the two surfactants showed that DTAB is more easily replaced than 2RenQ by the adsorption of the dendrimer. These results demonstrated that the simultaneous adsorption of the dendrimer and cationic surfactant on silica is considerably affected by the generation number of the dendrimer and the structure of surfactant. In addition, a simultaneous adsorption behavior of poly (ethyleneimine) and cationic surfactant on silica was very similar to that of the dendrimer and cationic surfactant.