To overcome the disadvantages generated by the loosened nanoparticle agglomerates dispersed in polymer composites, a chemical grafting method was applied to modify nano-alumina, silicon carbide and silicon nitride through covalently introducing polyacrylamide (PAAM) onto the particles. Sliding wear tests demonstrated that the frictional coefficient and specific wear rate of the nanoparticles/epoxy composites are lower than those of unfilled epoxy. Grafted nanoparticles reinforced composites have the lowest frictional property and the highest wear resistance due to the strengthening of the nanoparticle agglomerates and the enhancement of filler/matrix interfacial interaction resulting from the grafting polymers. Comparatively, graft treatment of nanoparticles is more beneficial to the improvement of the tribological features of the composites than the silane treatment that is used conventionally.

Preparation of nano-CdS particles with surface thiol modification by microemulsion method and their influences on the particle size distribution in highly filled polystyrene-based composites were studied. The modified nano-CdS was characterized by X-ray photoelectron spectroscopy (XPS), light absorption and emission measurements to reveal the morphologies of the surface modifier, which are consistent with the surface molecules packing calculation. The morphologies of the surface modifier exerted a great influence not only on the optical performance of the particles themselves, but also on the size distribution of the particle in polystyrene matrix. A monolayer coverage with tightly packed thiol molecules was believed to be most effective in promoting a uniform particle size distribution and eliminating the surface defects that cause radiationless recombination. Control of the particles size distribution in polystyrene can be attained by adjusting surface coverage status of the thiol molecules based on the strong interaction between the surface modifier and the matrix.

To tailor the interfacial interaction in magnetic metal nanoparticles filled polymer composites, the surfaces of iron, cobalt and nickel nanoparticles were grafted by irradiation polymerization. In the current report, effects of grafting conditions, including irradiation atmosphere, irradiation dose and monomer concentration, on the grafting reaction are presented. The interaction between the nanoparticles and the grafted polymer was studied by thermal analysis and X-ray photoelectron spectrometry. It was found that there is a strong interfacial interaction in the form of electrostatic bonding in the polymer-grafted nanoparticles. The dispersibility of the modified nanoparticles in chloroform was significantly improved due to the increased hydrophobicity.

To enhance the interfacial interaction in alumina nanoparticles filled polymer composites, an effective surface modification method was developed by grafting polystyrene and polyacrylamide onto the particles. That is, the alumina surface was firstly treated with silane, followed by radical grafting polymerization in aqueous or non-aqueous systems. Results of infrared spectroscopy and dispersiveness in solvents demonstrated that the desired polymer chains have been covalently bonded to the surface of the alumina particles. They also greatly changed their surface characteristics. In addition, effects of polymerization conditions, including ways of monomer feeding, concentrations of monomer and initiator, and reaction time, on the grafting reaction were presented. It was found that the growing polymer radicals and/or the grafted polymer chains had a blocking effect on the diffusion of radicals or monomers towards the surface of nanoalumina. This was due to the fact that the interaction between the solvent and the grafted polymers was weaker than that between the grafted polymers and the nanoparticles.

An irradiation grafting method was applied for the modification of nanoparticles so that the latter can be added to polymeric materials for improving their mechanical performance, using existing compounding techniques. The following items are discussed in particular, in this paper: (a) chemical interaction between the grafting monomers and the nanoparticles during irradiation; (b) properties including modulus, yield strength, impact strength and fracture toughness of the resultant nanocomposites; and (c) possible morphological changes induced by the addition of nanoparticles. Through irradiation grafting polymerization, nanoparticle agglomerates turn into a nano-composite microstructure (comprising the nanoparticles and the grafted, homopolymerized secondary polymer), which in turn builds up a strong interfacial interaction with the surrounding, primary polymeric matrix during the subsequent mixing procedure. Due to the fact that different grafting polymers brought about different nanoparticle/matrix interfacial features, microstructures and properties of the ultimate nanocomposites could thus be tailored. It was found that the reinforcing and toughening effects of the nanoparticles on the polymer matrix could be fully brought into play at a rather low filler loading in comparison to conventional particulate filled composites. Unlike the approaches for manufacturing of the other types of nanocomposites, including intercalation polymerization, the current technique is characterized by many advantages, such as simple, low cost, easy to be controlled and broader applicability.