Synthesis and characterization of poly (N-isopropylacrylamide)-coated polystyrene microspheres with silver nanoparticles on their surfaces

Dispersion copolymerization of styrene and a poly(N-isopropylacrylamide) ma cromonomer in ethanol water media has been successfully carried out in the presence of AgNO3. Nearly monodisperse polystyrene microspheres with diamet ers ranging from 530 to 1250 nm were obtained. Nanoscopic silver particles were generated on their surfaces via in situ reduction of Ag+ by radicals g enerated from the initiator, 2,2'-azobisisobutyronitrile (AIBN). The partic le sizes of both polystyrene microspheres and silver nanoparticles were aff ected by the initial AIBN, AgNO3, and macromonomer concentrations. The diam eters of the silvered microspheres and silver nanoparticles followed the re lationships D(n)proportional to[AIBN](0)(-0.107)[AgNO3](0)(0.083)[macromono mer](0)(-0.533) and d(n)proportional to[AIBN](0)(0.027)[AgNO3](0)(0.173)[ma cromonomer](0)(-0.137), respectively. Over 95.8% of the silver ions are con verted into zerovalent metal and immobilized on the microspheres, according to atomic absorption spectroscopy measurements. The silvered microspheres were characterized by transmission electron microscopy, atomic force micros copy, and FTIR, UV-visible, and X-ray photoelectron spectroscopy. The surfa ce-grafted PNIPAAm chains were found not only to serve as steric stabilizer s to prevent the flocculation of the polystyrene particles but also to adso rb the Ag nanoparticles onto the surface of the microspheres. A mechanism f or the formation of silvered polystyrene microspheres in dispersion copolym erization was presented.