The Pore Structure Control And Perforperties Analysis Of Co-precursors Organic-inorganic Silica Hybrid Aerogels

Aerogels have many excellent properties owing to their unique three-dimension network structures. Their brittle porous structures, however, usually result in the low strength and poor toughness, which restricts their practical applications. Therefore, it is a hotspot to improve the flexibility in the research fields of areogels. Among many methods, it is an effect method by choosing appropriate precursors with special functional groups to fabirate organic-inorganic hybrid aerogels, which benefits to realize the flexibility of aerogels based on retaining their traditional porous structural characteristics and properties.In this paper, the organic-inorganic hybrid silica aerogels(OISAs) were synthesized by using methyltrimethoxysilane(MTMS) and dimethyldimethoxysilane(DMDMS) as co-precursors via the sol-gel method and supercritical drying technology. Meanwhile, in order to improve their properties, the OISAs were modified by vacuum impregnation method. The structural characteristics, mechanical and thermal properties were analyzed.Co-precursors OISAs under different molar ratios of MTMS and DMDMS were prepared by using acetic acid and urea as catalysts, cetyltrimethyl ammonium bromide(CTAB) as surfactant via one one-step sol-gel method. Their micromorphologies and porous structural characteristics were analyzed, in which it is focus on the changes of porous structural characteristics of OISAs prepared under different proportions of the precursors. The results show that all the OISAs are noncrystaline porous materials. With the content increase of DMDMS, the sizes of skeletons and pores of OISAs transform from nanoscale to microscale. It is attributed to the introduction of extra –CH3 groups, which results in the increases of intermolecular repulsions and linear Si–O–Si bonds. Thus, the porous structures of OISAs can be controlled by adjusting the relative contents between MTMS and DMDMS.Modified OISAs were prepared by vacuum impregnating M5D0 nano-sols into M3D2 micro-pore matrixs. The analysis of micromorpholies and porous structures shows that micropores can be completely filled by nanoscale gel particles and the composite aerogels are formed. The molecular structures of OISAs can not be affected after vacuum-impregnation process. Because of the immersion of single-precursor M5D0 sols, the cyclic Si–O–Si bonds of modified OISAs increase. Compared with the sample M3D2, the specific surface area of modified OISAs increases and pore sizes reduce.Mechanical properties of OISAs under different molar ratios of co-precursors possess a larger difference. With the content increase of DMDMS, the plasticity of OISAs increases, but the strength decreased. Compared with single-precursor M5D0 aerogels, co-precursors M3D2 aerogels exhibit better flexibility. The states of OISAs are influenced by the drying methods. The flexibility and strength of areogles dried by supercritical drying are obviously better than those of areogles dried by atmospheric drying. The results of thermal transfer show that M5D0 aerogels possess the lowest thermal conductivity, but the thermal conductivity of M3D2 aerogels increases. Because the pore sizes and particle diameters increase with the content increase of DMDMS, the thermal insulation property of OISAs decreases. Modified OISAs by vacuum-impregnation method are provided with better comprehensive properties due to combine the advantages of mechanical and thermal properties of different aerogels.