Preparation And Properties Of Porous Silica Materials

The performance of porous silica materials depends on the design of the pore structure,so the development and the optimization of their preparation methods has always been the research hotspot in the field of porous materials.But until recently,the research on preparation methods mostly focuses on the formation mechanism and the morphological regulation principle of the pore structure.There are few studies on the correlation between pore structure parameters(such as pore size,porosity,etc.)and the properties of porous materials.However,research on the latter can not only reveal the relationship between porous material structure and performance,but also provide important guidance for the improvement of preparation methods,the precise construction of pore structure,and the effective improvement of the performance of porous materials.In this paper,three kinds of porous silica materials are prepared by the hard template method and template-free method,respectively.The correlation between the pore structure parameters and properties of porous silica materials has been further studied.The main research contents and results are listed as follows:(1)The y-ray radiation induced-disperion polymerization of divinyl benzene(DVB)in isopropanol was studied,polyvinylpyrrolidone(PVP)was used as the dispersant.The effects of dose rate and dispersant dosage on the particle size of the nanospheres during the synthesis of cross-linked polydivinylbenzene(PDVB)nanospheres are studied.As a result,monodisperse PDVB nanospheres with a diameter of 80～100 nm(dispersed in isopropanol)are prepared.The dispersion is directly mixed with the silica sol and then coated on the ultra-white glass.A porous silica film with a definite pore size is obtained after the removal of the PDVB microspheres by calcination.This film can increase the light transmittance of the ultra-white glass by 3%and is expected to be used as anti-reflection film.(2)With monodisperse polystyrene(PS)microspheres as the sacrificial template,a series of micron-sized hollow silica(H-SiO2)microspheres with different inner and outer radius ratios(r/R)are prepared by the precise control of the relative content of PS microspheres and tetraethyl orthosilicate.Further,H-SiO2 microspheres are blended with polydimethylsiloxane(PDMS)at different contents to obtain H-SiO2/PDMS composite rubber materials,and their thermal conductivities are measured.By comparing with the calculation results of the theoretical model of the thermal conductivity of hollow microspheres/polymer composites,it can be confirmed that the addition of H-SiO2 microspheres which have a complete hollow structure and an r/R value higher than 0.963 can reduce the thermal conductivity of H-SiO2/PDMS composite rubber.At the same time,when the weight content of H-SiO2 microspheres is no more than 5%,the mechanical properties of H-SiO2/PDMS composite rubber are also enhanced with the increase of the weight content of H-SiO2 microspheres.(3)The morphological changes of solid silica microspheres synthesized by the sol-gel method under the action of different catalysts during the high-temperature hydrothermal reaction are studied.Moreover,the pore-forming mechanism of porous hollow silica microspheres prepared by template-free method is proposed.Combined with the method of asymmetrically modified silica microspheres,the amphiphilic Janus eccentric hollow silica microspheres are prepared for the first time.The above research work provides a new idea for green accurate synthesis of porous silica film and hollow silica microspheres,and provide theoretical guidance for the development of silica materials.