Moduli of ordered polymer composites prepared by colloidal crystallization of nano- and micro-SiO2 spheres in crosslinked methacrylate resins

The extraordinary mechanical performance of nanomaterials found in nature has been attributed to the ordered arrangement of the components. Here, nano- and mico-composites containing either ordered or disordered arrangement of the spheres were compared. The nano- and micro-composites were formed using 19-45 vol% silica in crosslinked resins of triethylene glycol dimethacrylate (TEGDMA) and methyl methacrylate (MMA), in weight ratios TEGDMA/MMA of 100/0, 80/20 or 60/40. The silica nanoparticles, with sizes of 250, 500 and 1000 nm diameter, were silanated with methacryloxypropyl trimethoxysilane (MPS), MPS-SiO2, to promote bonding to the resin. The ordered nano- or micro-composites were obtained by colloidal crystallization and formed face-centered cubic arrays. Disorder was achieved by mixing two particle sizes or by addition of a coinitiator, dimethylaminoethyl methacrylate (DMAEMA). Ordered nano- or micro-composites had moduli 30% higher than similar composites in which disordered was introduced by mixing two size spheres, at the same loading, for all resin compositions. The greatest improvement occurred at the highest packing density of the spheres, 45 vol%. When disorder was introduced by addition of DMAEMA, the mechanical properties of the ordered and disordered composites were similar, since local but not long-range regions of order was also achieved in the latter case. (C) 2011 Elsevier Ltd. All rights reserved.