Structure-related diffusion in poly(methyl methacrylate)/polyhedral oligomeric silsesquioxanes composites: A molecular dynamics simulation study

Poly(methyl methacrylate) (PMMA) composites containing polyhedral oligomeric silsesquioxanes substituted with isobutyl (iBuPOSS) are studied by molecular dynamics simulation. Properties of the composites, mixing thermodynamics and diffusion behaviors of O2 and N2 were investigated. Introduction of abundant iBuPOSS remarkably enhances the mobility of PMMA chain, whose self-diffusion coefficient in the composites with 51.14 wt% iBuPOSS is five times greater than that in pristine PMMA. Below 15 wt% loading iBuPOSS molecules homogeneously disperse in the PMMA matrix, whereas above 20 wt% loading iBuPOSS molecules aggregate into crystallites, and iBuPOSS molecules have restricted motion in the composites. Cohesive energy density and solubility parameter increase with increasing the iBuPOSS loading. Through-pores that are the channels for gas diffusion are observed in the composites with higher iBuPOSS loading. The incorporation of iBuPOSS leads to an increase in the diffusivities of O2 and N2 in the composites at low iBuPOSS loading (≤15 wt%), and the composites with 15 wt% iBuPOSS have the highest diffusion coefficient of O2 and N2.