The Effect of Rubbery/Glassy Block Copolymer Brushes on the Dynamic Behaviors of Silica Particles in Nanocomposite Elastomer

Matrix-free elastomer nanocomposites with high strength was prepared by rubbery/glassy block copolymer-grafted silica nanoparticles (BCP-g-SiNP). Investigation of dynamic behavior of the nanocomposits can help us to know the dynamic structure and properties. However, the dynamic behavior of SiNP in the BCP-g-SiNP has not been well-studied. In this study, X-ray photon correlation spectroscopy (XPCS) was utilized to analyze the dynamics of BCP-g-SiNP with inner poly(butyl acrylate) and outer poly(methyl methacrylate).
The XPCS measurement revealed that the relaxation rates of SiNP were proportional to q value, indicating that the behavior of SiNP in the block copolymer-grafted SiNP was non-Brownian and hyperdiffusion motion. At the same q value, the relaxation rates increased dramatically as the temperature exceeded T_g. This is due to the outer PMMA phase changed to the rubbery state, and the restriction of SiNP motion by PMMA decreased. Moreover, during elongation, the relaxation rates of SiNP in the direction perpendicular to elongation was faster than in the direction parallel to elongation. The extended polymer chains might restrict the motion of SiNP, leading the slower relaxation rate of SiNP in the direction parallel to elongation.