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 chi(it), chi(is), and chi(ts) (chi is the differential contact energy between the different particles) for parameter values chi(it) = 0, +/-1 and -1 < chi(is), chi(ts) < 1. We have allowed negative chi 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, chi(is), and chi(ts) but only a weak function of chi(it), For chi(is), chi(ts) > 0, we observe dendrimer conformations, such as unimolecular normal micelles and inverted loopy micelles. However, for chi(is) < 0 or chi(ts) < 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.