Direct Relationship between Dispersion and Crystallization Behavior in Poly(ethylene oxide)/Poly(ethylene glycol)-g-Silica Nanocomposites

Abstract

The inclusion of polymer-grafted nanoparticles (PGNPs) can impart various functional properties to polymer nanocomposites (PNCs). For semicrystalline polymers, we can control the spatial dispersion of PGNPs and presumably use it to modulate the nucleation rate of the polymer. In this work, the correlation between the dispersion quality of poly(ethylene glycol) (PEG) grafted silica (PEG-g-SiO2) nanoparticles and the crystallization ability of poly(ethylene oxide) (PEO) nanocomposites is systematically investigated by varying the grafting density (σ, chains/nm2) and the value of P/N (P: molecular weight of matrix chains, N: molecular weight of grafted chains). The variation of PEG-g-SiO2 dispersion state was studied by morphological characterization and small-angle X-ray scattering (SAXS). It was found that, in contrast to the unmodified SiO2 and poly(methyl methacrylate) grafted silica (PMMA-g-SiO2), PEG-g-SiO2 (high σ and low P/N) can increase the nucleation rate of PEO even under conditions where they are well dispersed in the PEO matrix. Evidently, the nature of the graft, i.e., amorphous PMMA vs. crystallizable PEO, has profound consequences in this context, a novel result that has not been anticipated based on previous work. NP aggregation occurs at higher P/N values and limits the effectiveness of the grafted PEG on the crystallization ability of PEO nanocomposites. Based on differential scanning calorimetry (DSC) and polarized light optical microscopy (PLOM) characterization, we deduced that the increased nucleation density at high σ and low P/N has a strong impact on accelerating the overall crystallization of PEO nanocomposites.