Incorporation of alkyl-functionalized silica nanoparticles into hydrophilic epoxy and hydrophobic polystyrene matrices

The homogeneous dispersion of nanosized fillers in a polymeric matrix is crucial for improving the mechanical and thermal properties of composites. In this study, the dispersity of silica nanoparticles (SNPs) in the hydrophilic epoxy and hydrophobic polystyrene (PS) matrices was examined. As the unmodified SNPs were hydrophilic, they dispersed well in the epoxy matrix, but agglomerated in the PS matrix. We also explored the effects of different aliphatic chain lengths (hydrophilic vs. hydrophobic: unmodified, methyl, propyl, and octyl) on the dispersity of nanoparticles in the polymer. The alkyl-functionalized SNPs were more uniformly dispersed than the unmodified SNPs in the PS matrix. Comparing the different alkyl chains, the propyl-functionalized SNPs exhibited the most homogeneous dispersion in the polymer, thereby increasing the mechanical properties. The octyl-functionalized SNPs agglomerated slightly, which might be due to their chain interaction (entanglement). The size of SNPs was controlled (60, 120, and 180 nm) via sol-gel synthesis, and the SNP with the smallest diameter (60 nm) showed the slight enhancement in mechanics and dispersion compared with SNPs with diameters of 120 and 180 nm. The SNP size, hydrophilicity, functionality, and aliphatic chain length on SNP surfaces investigated in this study can be useful for various nanocomposite applications.