Preparation Of Monodisperse Polystyrene Microspheres And Preliminary Study On The Magnetization Process

Magnetic polymer microspheres with the characteristic of samll size, large surface area and active surface groups have been wildly used in various biochemistry and medical fields. Monodispersion, controllable size, high magnetism content, and concurrently magnetic responsiveness are required in actual application. At present, the common production method is to entrap magnetic particles into functional polymer materials or to disperse magnetic powders into organic monomer and then to polymerize. But the magnetic polymer microspheres prepared by above techniques can't meet the requirements. Although the immune magnetic microspheres (IMMS)-Dynabeads? have good properties, it is too expensive to be accepted by many customers due to the two-stage swelling technique used. As a result, membrane emulsification-drying in liquid technique was established in present work to prepare monodisperse and size controllable polystyrene (PS) microspheres. The characteristic of PS microspheres and the magnetization process were studied in order to provide technology producing magnetic microspheres carrier of good capability and low preparation cost.Monodispered emulsion droplets can be prepared in mild condition withmembrane emulsification technology, and the size of the droplets can becontrolled by the pore size of membrane. Integrated with the dying in liquidtechnique, monodispered PS microspheres with a size of 2~20μm weresuccessfully prepared. The size of PS microspheres was about 2.1~2.4 times of thepore size of SPG membrane, and was slightly bigger with a higher PSconcentrations. The distribution of the size of PS microspheres was stronglydependent on the emulsification pressure and the concentrations of emulsifier.When pressure is high and emulsifier concentrations are low, the size distributionbecame wide. Other conditions, such as the oil/water ratio, the temperature andthe vacuum degree of drying-in-liquid, can only slightly affect the size and sizedistribution of the PS microspheres.PS microspheres with loose surface and inner structure were prepared whenthe PS concentration was low or toluene added as porogenic agent. The hollow PSmicrospheres with smooth surface　were prepared by adding n-Hexadecane asporogenic agent. PS microspheres prepared by W/O/W emulsion are hollowspheres with porous surface,but the size distribution is not as good as thatprepared by O/W emulsion. Magnetic PS microspheres were prepared by magnetizing different types ofPS microspheres. The magnetic material inside was Fe3O4 determined by X-raydiffraction spectrum. The suspension property and magnetic responsiveness wereproved to be ideal. It was shown that PS microspheres prepared by W/O/Wemulsion were much easier to load magnetic substances. However, the adsorptionof magnetic material on the surface of microsphers was still a serious problem. In conclusion, the method of membrane emulsification-drying in liquid isquite suitable to be used for the preparation of magnetic microspheres carrier.