A Monte Carlo study of amphiphilic dendrimers: Spontaneous asymmetry and dendron separation

We study via Monte Carlo simulation the conformation of amphiphilic dendrimers for which terminal monomers (t) and internal monomers (i) interact differently with the solvent (s). Specifically, we have studied g=3,6 dendrimers as a function of χit, χis, and χts (χ is the differential contact energy between the different particles) for parameter values χit=0,±1 and −1 smaller than χis, χts smaller than 1. We have allowed negative χ values in order to model attractive polar interactions (e.g., hydrogen bonding) which are believed to be important in many dendrimer/solvent systems. We find the “phase diagram” of dendrimer conformations to be extremely rich and to be a strong function of g, χis, and χts but only a weak function of χit. For χis, χts greater than 0, we observe dendrimer conformations, such as unimolecular normal micelles and inverted loopy micelles. However, for χis smaller than 0 or χts greater than 0, we observe more exotic molecular conformations, for example, the spontaneous development of asymmetry and dendron separation. These properties are analyzed in terms of snapshots as well as more quantitatively in terms of the radii of gyration, radial density profiles, pair-correlation functions, degree of asymmetry, and dendron overlap factor. By exploiting the dramatic conformational changes under different solvent conditions, we suggest the possibility of using amphiphilic dendrimers as stimuli-responsive smart materials