Adsorption of Charged Dendrimers: A Brownian Dynamics Study

Abstract

The adsorption of isolated charged dendrimers onto oppositely charged flat surfaces is studied in this work using Brownian dynamics simulations. The dendrimer is modeled as a freely jointed bead-rod chain in which excluded-volume interactions are modeled by a repulsive Lennard-Jones potential and bead-bead and bead-surface electrostatic interactions are described by screened Coulombic potentials. Adsorption behavior is studied as a function of inverse screening length, dendrimer generation, and dendrimer charge distribution. Adsorbed dendrimers adopt a disclike conformation in which they flatten in the direction normal to the surface and expand in the direction parallel to the surface. As the inverse screening length increases, the dendrimer expands in the normal direction and contracts in the parallel direction, adopting a conformation that is more stretched in the normal direction. When the inverse screening length becomes sufficiently large, the dendrimer desorbs and adopts a spherelike conformation. Bead density profiles show that adsorbed dendrimers form a two-layer structure, with one layer corresponding to adsorbed beads and a second, less dense layer corresponding to beads one rod length away from the surface. They also reveal how the distribution of monomers within the dendrimer and near the surface can be tailored by changing various problem parameters. The results presented here are expected to be helpful in providing qualitative guidance for dendrimer design in various applications.