Preparation And Characterization Of SiO₂Core/Shell Matericals

Among kinds of nanomaterials,there is Core/Shell nanoparticle.As the size of materialscome to the level of nanometer,the materials have immense changes in physical andchemical properties.These changes lead to some novel properties like surface effect,bulkeffect,quantum size effect and macro quantum tunneling effect. The most importantcharacters come with the properties mentioned above are as follows: First, the smallsize of the particles, which leads to an increased surface area to volume ratio and as aresult the domain where quantum effects predominate is entered. Second,the increasingsurface area to volume ratio leads to an increase in the dominance of the surface atoms ofthe nanoparticle over those in its interior.The properties of kinds of nanoparticles are depended by the shape.Not only thesymmetrical (spherical) shape， there are a varity of other shapes such ascube,prism,hexagon,octahedro,disk,wire,rod,tube,etc.Depended by the composites ofdifferent parts,nanoparticles can also be classified byInorganic/Inorganic,Inorganic/Orga-nic,Organic/Inorganic,Organic/Organic.Thenanoparticles share all the properties of different composite.Due to its specialstructure,the Core/Shell nanoparticle shows many exciting properties to realize itsfunctionalization and directional transformation.Compared with singleparticles,Core/Shell particles have many practical applications,especially in thebiomedical and electronics fields.In the biomedical field,Core/Shell nanoparticles aremainly used for controlled drug delivery,bioimaging,cell labeling, biosensors and intissue engineering applications,etc.It also shows its novel properties in specialceramics,synthesis of hollow nanoparticles and catalytic.The preparation of SiO2/SiO2Core/Shell nanoparticle is introduced.Step1,monodispersed SiO2nano spheres were prepared.Step2,in both basic and acidenvironment,the shell were coated on the SiO2nano spheres.Conclusion are as followed:(1)The SiO2nano spheres,which were prepared respectively in dehydrated alcohol and butanol by hydrolytic condensation method,have uniform size and are wellmonodispersed.The particle size lies in sub-micron level.(2)Increasing the molecular weight of the reaction medium will slow down thereaction rate of the system and enlarge the particle size of SiO2.In methanol medium,SiO2particles are the smallest and worst dispersed.In ethanol medium,the particle size of SiO2is about200nm in the middle.In the butanol medium,SiO2microspheres get the biggestsize for about400nm.The distribution of size is widened,but the sphericity becomesbetter and the agglomeration between microspheres gets improved.(3)With more surfactant,this hydrolytic condensation method in basic environmentprepared bigger sized SiO2microspheres and thicker shell.Then,the preparation of PS/SiO2Core/Shell nanoparticle is introduced.Step1,polystyrene (PS) microspheres were prepared by emulsion polymerization.Step2,coated these PS microspheres with SiO2shell.Conclusion are as followed:(1)Emulsion polymerization is an effective way to prepare monodispersed PSmicrospheres.These experiments prepared PS microspheres with good sphericity,smoothsurface and good monodispersity.(2)To prepare monodispersed and SiO2coated PS/SiO2Core/Shell nanoparticle,thispaper introduces an easy method with simple progress and low cost.(3)The polymerization reacted in water medium without using comonmer.Inste-ad ofexpensive cationic initiating agent AIBA,a cheap anionic initiating agent APS wasused.Besides,before coating progress,there’s no nead to exchange solvent orcentrifuge.So the preparation progress is simplified.(4)The prepared Core/Shell nanoparticles get bigger radius and more roughwith more dosage of ammonia.So,adjustting the dosage of ammonia can obtain PS/SiO2Core/Shell nanoparticle of needed size.