Adsorption-desorption effect on physical aging in PMMA-silica nanocomposites

Poly(methyl methacrylate) (PMMA)-silica nanocomposite was used to study the adsorption-desorption of polymer chains on the surface of silica nanoparticles. We demonstrate that the adsorption-desorption is a dynamic process with respect to temperature and time. The adsorption condition could be changed after annealing at T-g + 16 C. Then, the physical aging under confinement was investigated under different adsorption conditions. At relatively high aging temperatures, we reveal a one-step equilibration with reduced enthalpy recovery of nanocomposite compared with neat PMMA. In contrast, the aging rate of composite is decelerated and then accelerated after a long period of aging at a relatively low temperature due to the emergence of two-step equilibration. Furthermore, the material system with a higher adsorption fraction exhibits a stronger confinement effect on aging. We speculate that the transition from one-step to two-step equilibration corresponds to the activation of segmental alpha & PRIME; relaxation in the interfacial region. The adsorbed chains result in restrained segmental alpha & PRIME; and beta & PRIME; relaxation and low enthalpy recovery at relatively high aging temperatures. At a relatively low temperature, the interfacial alpha & PRIME; relaxation with high released enthalpy comes to the surface after a long aging time, inducing the elevated aging rate.

Automated summary

In this study, the adsorption-desorption of polymer chains on the surface of silica nanoparticles in PMMA-silica nanocomposite was investigated. The results showed that the adsorption-desorption process is dynamic and influenced by temperature and time. The adsorption condition can be altered through annealing, and the physical aging behavior under different adsorption conditions was analyzed.