Preparation And Research Of Silica-Polyacrylate Core-Shell Composite Micro-spheres

Inorganic particles-polymer hybrid micro-spheres are composite materials combined with inorganic and organic phases.Small size of the silica particles are widely used in inorganic materials due to its extensive sources,non-toxic,pollution-free and high strength.Because of their great variety,easy polymerization and excellent composite performance in coatings,adhesives,textiles and so on,acrylate monomers become one of the best polymer species of composite materials.In this dissertation,sillica-polymethyl methacrylate core-shell morphology composite micro-spheres were successfully obtained via mini-emulsion polymerization.All the detailed research contents and experiment results are as follows:(1)The preparation of silica particles.The optimal parameters of 41-491nm silica particles were first synthesized through stober sol-gel method with tetraethylorthosilicate(TEOS)as raw materials,ammonia(NH3 · H2O)as catalyst and absolute ethanol(C2H5OH)as reaction medium.It was found that the average size and morphology was significantly influenced by the dosage of NH3 · H2O according to nano particle and potentiometric analyzer and Scanning Electron Microscopy(SEM)photos,with the increasing density of NH3 ·H2O,the particle size of silica increased rapidly.The particle size of silica had a close relation with the concentration of TEOS,it increased slightly,respectively.In a suitable range,absolute C2H5OH had little influence on the particle size.The average diameter of 333nm homogeneous silica particles were synthesized under these conditions:the volume of NH3-H2O is 3ml,TEOS is 4.2ml,absolute C2H5OH is 62ml,H2O is 25ml,reaction temperature is 25 ? and holding time is 2 hours.(2)The surface modification of silica particles.The average diameter of 333nm homogeneous silica particles were dispersed in absolute C2H5OH and functionalized by silane coupling agent methacryloylpropyltrimethoxysilane(y-MPS).The enrich hydroxyl of silica surface was reacted with the hydroxyl of hydrolysed y-MPS.Thus,silica particles were grafted with reactive groups.The grafting yield was characterized by thermogravimetric analysis(TGA),contact angle(CA)and elemental analysis(EA)and the pH value,the amount of H2O and?-MPS on modification effect were discussed.The modified silica particles which weight loss rate was 4.2%and the maximum contact angle could reach 126° were obtained in the presence of acid conditions,after 24 hours at pH value of 5,the dosage of H2O is 0.35g,coupling agent ?-MPS is 1g and absolute C2H5OH is 40g,backflowing under 80 ? at atmospheric pressure.(3)The synthesis of ?-MPS-SiO2-PMMA composite micro-spheres.The?-MPS-SiO2-PMMA composite micro-spheres were gained through mini-emulsion polymerization in the presence of silica particles coated with ?-MPS-SiO2 as core materials and MMA as the shell monomer.The effects on the size and morphology of micro-spheres such as the quality of MMA/SiO2 ratio,surfactant(SDS)concentration,the size(150nm,333nm)of silica particles and soft monomer BA compared with hard monomer MMA were investigated.The morphological structure of the core-shell composite particles were confirmed by Transmission Electron Microscopy(TEM).We could get clear and perfect coating composite micro-spheres when the ratio of MMA/SiO2 was 3:1 and the concentration of SDS was 10mmol/L.In this way,the weight loss rate of particles was 11.2%.As this point,The shell layer became thick when reduce the size of the silica particles through diameter analysis and TEM images;Besides,it could not form obvious core-shell micro-spheres while using BA replacing MMA under the same experimental conditions.