Controllable Self-Assembly of Amphiphilic Dendrimers on a Silica Surface: The Effect of Molecular Topological Structure and Salinity.

Abstract

The adsorption kinetics and equilibrium of amphiphilic dendrimers based on poly(amidoamine) modified with a dodecyl chain, GnQPAMC12 (n represents the generation number), with different generation numbers at a silica-water interface have been investigated. The effect of molecular shape with different charge characteristics on the adsorption kinetics, adsorption isotherms, and the conformation of a self-assembled layer has been elucidated. For the adsorption kinetics, two steps were observed including the adsorption of individual molecules at concentrations below the critical micelle concentration (cmc) and the predominant adsorption of aggregates above the cmc. However, the adsorption isotherm, as a function of the generation number, presented an exceptional characteristic, in which a decrease in adsorption mass with different levels occurred in a high generation of amphiphilic dendrimers, depending on the balance of hydrophobic interaction and electrostatic repulsion. Atomic force microscopy imaging showed that flattened films with pores (spacing) of various shapes and roughness of 3-4 nm were formed, of which the pores (spacing) decreased obviously as the generation number increased. The addition of electrolyte (NaBr) has a great effect on the film morphology formed by the G3QPAMC12 dendrimer adsorbed at the silica-water interface, showing that the film became closer with smaller pores with increased NaBr concentration.