Modification of macromolecular dynamics in polyacrylic hybrid nanocomposite with un-treated SiO2 nanoparticles

The viscoelastic properties of polyacrylic/SiO2 nanocomposites were investigated; nanoparticles content varied up to 3 wt%. The results showed that the concentration of SiO2 influences both the molecular weight, as well as the thermal and mechanical properties. As-cast films show optical transparency and no evidence of macro-aggregation. The elemental mapping analysis confirmed the presence of Si throughout the films and scanning electron microscopy (SEM) show evidence of dispersed micro-aggregates at high SiO2 concentrations. Differential scanning calorimetry (DSC) and shear rheometry showed that the glass transition temperature, Tg, significantly decreased relative to neat polyacrylic, i.e., ΔTg < 0, and this effect was not associated with molecular weight. Hardness and tensile modulus decrease nearly 64% and 70% respectively relative to the neat polyacrylic. Dynamic mechanical analysis (DMA) showed higher shear elastic modulus and shift of maximum of tan δ in the polyacrylic. The results suggest a modified polymer molecular dynamics driven by interactions of the un-treated nanoSiO2 with the matrix.