A negatively charged monodisperse polystyrene (PSt) seed emulsion was first synthesized via batch emulsifier-free emulsion polymerization

and polyethyleneimine (PEI) aqueous solution was then added into the diluted emulsion to modify the particle surface at 25℃ to prepare the positively charged PSt seed particles.Then

the core-shell PSt/TiO2composite microspheres were obtained by adding the diluted modified PSt seed emulsion into the medium of ethanol containing certain amount of tetrabutyl titanate (TBT).Influences of pH and TBT amount on the morphology of PSt/TiO2 core-shell composite microspheres were investigated by TEM and SEM observation.Results showed that it was difficult to form PSt/TiO2 core-shell microspheres under acidic conditions

and a uniform TiO2 shell with about 29 nm in thickness was obtained when pH increased to 7.2

and then the thickness of the TiO2 shell increased with the increase of pH value.When pH was 11.0

the thickness of the TiO2 shell reached 70 nm

but some of the composite microspheres were partially encapsulated.With the increase of TBT amount from 0.01 g to 0.16 g

the thickness of PSt/TiO2core-shell composite microspheres gradually increased from about 0 nm to 60 nm when the amount of PSt seed emulsion was 0.5 g (solid content was 4% by weight) and pH was controlled at 8.5. While the TBT amount increased to 0.32 g

the thickness of the TiO2 shell reduced to 12 nm

and the surface of the composite microspheres became rough gradually.After that

with the increase of TBT amount

the thickness of the TiO2 shell decreased

and a number of TiO2 nanoparticles appeared.The voided TiO2 microspheres were obtained by calcining the PSt/TiO2 composite microspheres at 500℃ for 4 h when the thickness of TiO2 shell in the composite microspheres reached a certain level.