Controlled Preparation And Mechanism Of Silver And Polystyrene Nanoparticles Via Emulsion Technology

Nanomaterials have great potential application since these nanoscale particles can exhibit peculiar optical, electrical, magnetic and thermal properties due to Surface effect, volume effect, quantum size effect and macroscopic quantum tunneling effect and so on. However, the stability and the controllability of their size and morphology becomes an important factor to limit the further development. This work aims at preparing stable size&morphology controlled metal nanoparticles and polymer nanoparticles as well as studying the mechanmism.Silver nanoparticles are prepared by the chemical reduction in reverse microemulsion. XRD, TEM, UV-Vis and other characterization results show that the formation and stability of microemulsion system are affected by the changing parameters, the reaction time is effectively shorten by selecting OP-10 instead of AOT as emulsifier, the reactants exchange between the droplets via attractive interactions is the control factor of dynamics in the reverse microemulsion system. The obtained stable monodispersed silver nanoparticles under optimum conditions are spherical monocrystalline with an average diameter of 15.2nm.The polystyrene nanoparticles are rapidly synthesized in emulsion polymerization via using the silver ammonia complex as accelerator to promote the decomposition of potassium persulfate. We first discuss the reaction temperature, stirring speed, oil-water mass ratio, emulsifier density etc influence in the period of styrene emulsion polymerization to determine the best reaction conditions. Kinetic results show that under the catalysis of KPS-silver ammonia, the styrene monomer conversion rate is significantly enhanced, the polymerization ends in a short time with the maximum rate at the beginning followed by continuous decreasing and the conversion is complete. The adding of silver ammonia decreases the initiator activation energy of potassium persulfate, lowering the minimum polymerization temperature of styrene and significantly decreasing the apparent activation energy of the reaction system.FT-IR, DSC, TEM and GPC characterization results showed that KPS-silver ammonia does not affect the structure, morphology and glass transition temperature of polystyrene. But under its effect, when compared with the traditional emulsion polymerization, the sizes of polystyrene nanoparticles are smaller, the size and size distribution are both decreased with increasing temperature; the molecular weight reduce by half with a slightly wider distribution. The addition of silver ammonia has a dual role, not only promoting the decomposition of potassium persulfate so that the styrene polymerization does not comply with the classical polymerization mechanism for the polymerization sitting in the micelles and there only exist micellar nucleation, but also assisting the surfactant to stabilize latexes. It has just started to use silver ammonia as promoter for the rapid polymerization of styrene and it's of great significance both in theory and industrial applications for depth study of related issues such as the promotion mechanism, the effect in other monomer polymerization and so on.