Polymer–nanoparticle interfacial behavior revisited: A molecular dynamics study

Abstract

By tuning the polymer–filler interaction, filler size and filler loading, we use a coarse-grained model-based molecular dynamics simulation to study the polymer–filler interfacial structural (the orientations at the bond, segment and chain length scales, chain size and conformation), dynamic and stress–strain properties. Simulated results indicate that the interfacial region is composed of partial segments of different polymer chains, which is consistent with the experimental results presented by Chen et al. (Macromolecules, 2010, 43, 1076). Moreover, it is found that the interfacial region is within one single chain size (R_g) range, irrespective of the polymer–filler interaction and the filler size, beyond which the bulk behavior appears. In the interfacial region, the orientation and dynamic behaviors are induced by the interfacial enthalpy, while the size and conformation of polymer chains near the filler are controlled by the configurational entropy. In the case of strong polymer–filler interaction (equivalent to the hydrogen bond), the innerest adsorbed polymer segments still undergo adsorption–desorption process, the transport of chain mass center in the interfacial region exhibits away from the glassy behavior, and no plastic–like yielding point appears in the stress–strain curve, which indicates that although the mobility of interfacial polymer chains is restricted, there exist no “polymer glassy layers” surrounding the filler. In addition, it is evidenced that the filler particle prefers selectively adsorbing the long polymer chains for attractive polymer–filler interaction, validating the experimental explanation of the change of the bound rubber (BR). In short, this work provides important information for further experimental and simulation studies of polymer–nanoparticle interfacial behavior.