Facile preparation of superparamagnetic Fe3O4/poly(St-co-MPS)/SiO2 composite particles with high magnetization by introduction of silanol groups.

: Fe3O4/poly(St-co-MPS) particles were prepared by encapsulation of Fe3O4 nanoparticles into copolymers of styrene (St) and 3-trimethoxysilylpropylmethacrylate (MPS) (poly(St-co-MPS)) prepared by miniemulsion copolymerization. It is found that the structure of the Fe3O4/poly(St-co-MPS)/SiO2 composite particles prepared by direct silica deposition on surface of the Fe3O4/poly(St-co-MPS) particles is dependent on the volume fraction of MPS used in the copolymerization. It is identified that the surface of the Fe3O4/poly(St-co-MPS) particles becomes more negatively charged with increased volume fraction of MPS used in the copolymerization, attributed to the increased amount of the silanol groups on the particles surface. Introduction of silanol groups on the particle surface is effective to improve the dispersibility of the Fe3O4/poly(St-co-MPS) particles and their compatibility with silica, allowing the facile preparation of Fe3O4/poly(St-co-MPS)/SiO2 composite particles with defined core-shell structure. The as-prepared Fe3O4/poly(St-co-MPS)/SiO2 composite particles show high magnetization, for example, saturation magnetization of the particles with average size of 140 nm and 6 nm silica shell is as high as 45 emu/g at 300 K.