Aggregation of Grafted Nanoparticles in a Polymeric Matrix

A common phenomenon for polymer-grafted nanoparticle (PGNP) systems is that NP aggregation spontaneously occurs at a specific ratio of the chain length N_g of the grafted chains to the matrix chain length N. This aggregation is generally considered to be entropic in origin and can be attributed to the autophobic dewetting of the grafted chains. Here, we incisively probe the microscopic driving force governing PGNP aggregation through a series of large-scale multi-particle simulation studies. The matrix chain length, graft chain length, and volume fraction were varied. Analysis of our simulations indicate that aggregation take place only at unexpectedly low ratios of N_g/N. Further, simulations tuning the interaction mismatch between nanoparticles and polymer chains indicate that some form of enthalpic interplay between the polymer chains and NPs is significant in controlling the PGNP aggregation that is observed experimentally. These results suggest that entropy alone is probably not the only factor driving nanoparticle aggregation in nanocomposites.