New understanding of filler dispersion, interfacial interaction and mechanical strengthening of rubber nanocomposites by combining simulation and experimental studies

摘要

Novel information about filler dispersion and flocculation, rubber-filler interfacial interaction and its mechanical strengthening is obtained by carrying out a detailed coarse-grained molecular dynamics simulation and experimental study. Firstly we probed the filler dispersion state by mainly tuning the polymer-filler interaction, and interestingly the relatively optimal dispersion is obtained for polymer-filler interaction with moderate strength. For polymer-filler interfacial interaction, the structural and dynamic properties are characterized away from the filler surface by tuning the polymer-filler interaction, filler size and filler loading. It is found that the ranges of the perturbed region of polymer chains are all confined approximately within the radius of gyration (R_g) around the filler. Moreover, the packing of the polymer chains on the filler surface is induced by the interfacial enthalpy. Remarkably, our simulated results provide conclusive evidence that the interfacial region is composed of partial segments of different polymer chains, supporting the experimental assumption from Chen et al. (Macromolecules, 2010, 43, 1076). Meanwhile, from the point of kinetics and thermodynamics, we conclude that it is impossible for polymer chains to be fully anchored on the filler surface to form the so-called "glassy layer" surrounding the filler, in contrast with the literature (Merabia et al. Macromolecules, 2008, 41, 8252). In the case of strong rubber-filler interaction (equivalent to the hydrogen bond), the interfacial chains are suppressed to some extent but still undergo the adsorption/desoprtion process, exhibiting greater dynamics than that of the glassy state. A novel percolation phenomenon is found for its mechanical strengthening, the concept of the critical particle-to-particle distance (CPPD) is put forward to uncover the mechanism, highlighting that the strength enhancement mainly originates from the formation of parallel-arraying stretched polymer chains between neighboring particles.