Adsorption of Poly(amidoamine) Dendrimers on Alumina/Water and Silica/Water Interfaces

Abstract

Adsorption characteristics of poly(amidoamine) dendrimers at the alumina /water and silica /water interfaces at pH 5 were investigated by measuring the amount of dendrimers adsorbed, ζ potential, and dispersion stability of suspensions. Two kinds of dendrimers were used dendrimers with surface carboxylate groups for generations 0.5, 1.5, 2.5, 3.5, 4.5, and 5.5 (G0.5−5.5) and amino groups for generations 0, 1, 2, 3, 4, and 5 (G0−G5). The microenvironmental properties of dendrimers adsorbed on the particles were also estimated using spin and fluorescence probes. In the adsorption of dendrimers with surface carboxylic groups on positively charged alumina particles, the amount in weight of the dendrimers adsorbed increased with increasing generation from G(0.5) dendrimer to G(5.5) dendrimer. The results of ζ potential and dispersion stability indicate that the earlier generations of G(0.5 and 1.5) dendrimers behave as ordinary electrolytes, while the later generations of G(2.5−5.5) dendrimers behave as anionic surfactant or polyelectrolyte for the alumina dispersion, resulting in a dispersion−flocculation−redispersion sequence with the dendrimer concentration. A similar adsorption behavior was observed for the dendrimers with surface amino groups on negatively charged silica particles. It was found that the amounts adsorbed of the dendrimers with surface carboxyl groups are considerably greater than those with surface amino groups. Further, the microenvironmental polarities of dendrimers adsorbed for both systems were lower than those of dendrimers in the supernatants.