Dry monodisperse silica particles (spherical, 500-nm diameter) were redispersed in selected solvents and monomers (e.g. triethyleneglycol dimethacrylate, TEGDMA) to form sediments or dispersions with ordered particle arrangements. Ordering was evaluated by microscopy and mechanical properties of the composites were measured using compression tests (n = 6).
A face-centered cubic packed structure could form in both the sediment from silica dispersions in polar solvents and stable dispersions in TEGDMA. Dimethylaminoethyl methacrylate (DMAEMA) was found to disrupt an ordered structure when non-silanized silica particles were used. Silanization with 3-methacryloxypropyl trimethoxysilane (MPS) promoted filler ordering. Standard compression tests on composites containing 60 wt % silica in TEGDMA with or without DMAEMA indicated that DMAEMA had a clearly significant effect (p < 0.05) on failure strain, compressive strength, and toughness, and a marginally significant effect on modulus (p = 0.12).
Significant increases in compressive strength (16 % ), failure strain (71 % ), and toughness (135 % ) were observed for composites with ordered filler compared to non-ordered composites.