Property improvements of in situ epoxy nanocomposites with reduced interparticle distance at high nanosilica content

SiO2/epoxy nanocomposites were formed in situ via a special sol-gel technique supplied by hanse chemie AG, in which silica nanoparticles with an average diameter of 25 nm were almost perfectly dispersed in the epoxy matrix. The static/dynamic modulus, microhardness, and fracture toughness of the nanocomposites were found to be enhanced with increasing silica content up to 14 vol.% (23 wt.%). The results confirmed that the homogeneously distributed nanoparticles are able to improve both the stiffness and toughness of the epoxy. Significant improvements were observed for both stiffness and toughness when the interparticle distance was smaller than the nanoparticle diameter. Under this condition, the interphase may construct a three dimensional physical network, which will finally dominate the performances of these nanocomposites. From the experimental observations, it is proposed that the critical thickness of the interphase surrounding a spherical nanoparticle is in the range of the particle's radius, which is crucial to many modelling studies.