Facile surface modification of silica nanoparticles with a combination of noncovalent and covalent methods for composites application

A simple, efficient and cost-effective approach for preparing surface modified silica nanoparticles (SiO2) was developed by combining noncovalent and covalent modification process. Tetraoctylammonium bromide (TOAB), which is usually used in aqueous systems as surfactant, was introduced into organic solvent prior to covalent modification in order to assist the dispersion of pristine SiO2 nanoparticles noncovalently. Then covalent modification was accomplished by radical grafting polymerization. The successful modification of SiO2 was confirmed and as-prepared modified SiO2 possessed smaller particle size and larger grafting rate than SiO2 prepared by conventional method. More interestingly, the amount of TOAB used in the noncovalent process had a direct impact on the particle size and grafting rate. Meanwhile, poly (methyl methacrylate) (PMMA) was selected as the matrix to investigate the effect of as-prepared modified SiO2 on the property of polymer-based nanocomposites. Owing to the improved modification effect, the prepared PMMA/SiO2 nanocomposites showed far more excellent mechanical properties compared to those with SiO2 prepared by conventional modification method. The tensile strength and flexural strength could be enhanced by as much as 80.6% and 127.3% compared to those of pure PMMA, respectively. The highlight of this work lies in the fact that remarkable improvement had been achieved with the facile combination of noncovalent and covalent process, which is relatively easy to realize and manipulate compared to other sophisticated methods.