Sio <sub> 2 </ Sub> Gel / Glass Micro-structure Formation, Characterization And Control

The preparation of optically active composite is a promising alternative to obtain a kind of new and competitive product for information technologies, and has attracted the global attention. The Sol-Gel method has been widely used in preparing organic-inorganic materials because of its advantages such as low processing temperature.In this paper, the effects of processing parameters to microstructure of Gel are reviewed and have provided the theoretic foundation for preparing good inorganic materials. We have researched the hydrolysis and condensation of TEOS, formation, structure and control methods of SiO2 Gel by using GPC, BET and IR methods. Emphasize on the effect of ratio of hydrolysis and condensation to distribution of molecular weight of sol ^ condensation manner -. distribution of grain of gel and structure of gel, the effect and mechanism of organic radical modification to structure. We have gained many important results for preparing structure controllable inorganic materials.The results on effect of pH between 2.0 to 4.5 to structure indicate that: when pH is between 2.0 to 2.9, the polymer chains are formed in the first stage because the hydrolysis ratio is lager than ratio of condensation. With the increase of pH chain-condensation increases, the planar and three-dimensional chains are developed and the gel grains grow, so the simplified pores in 6A and 40A come forth. At the same, the special surface area increase, the material develops from non-pore to meso-pore. When pH is from 3.0 to 4.5, with the increase of hydrolysis and decrease of condensation, the molecular weight increase, and the chains become longer the grains grow, but they have no simplified distribution, so there are no simplified pores. The special surface area and pore volume decrease greatly, and the materials developed from meso-pore to micro-pore. In conclusion we can adjust gel from micro-pre to meso-pore to non-pore by controlling the pH.The results of effect of ratio of H2O/Si (Ro) to structure indicate that: Ro affects the structure by changing the ratio of hydrolysis and condensation. When Ro <2, the special surface area and pore volume are very small, the materials have many micro-pore. With the increase of Ro, the molecular weight, condensation and grain size increase the special surface area and pore volume increase greatly. When Ro reach 2 the special surface area is largest, and the gel has distinct simplified micro-pore and meso-pore. When the Ro keep on increasing, the pore volume and intensity of simplified pore increase, and there will be many small simplified meso-pores. In a word controlling Ro is another effective way to modulate the structure of SiO2 gel.In order to decrease the quantity of micro-pore, change the polar environment and increase the tenacity of xerogels, we have researched on the modification of xerogels. The results indicate that organic radical will change the ratio of hydrolysis and condensation of precursor and change the microstructure of xerogels, because they have different Electro-negation and size. So modification is another way to control structure of SiO2 gel.The heatment of xerogels can change the microstructure. With the deep hydrolysis-condensation of xerogels, escaping of organic solvent and adjust of Gel grain, the micropore are reduced, the mesopore are reformed.The blend of MMA into the xerogels will not change the ratio of hydrolysis and condensation. They will inhabit in the meso-pore of xerogels. The effect of organic optically active molecular to Gel is similar to MMA when mixed with xerogels.The research can provide foundation theory for preparing good micropore materials by selecting optimal processing such as pH, ration of H2O/Si, kind of precursors and blending organic molecules to Gel. This will inevitably prompt the research of organic-inorganic optical composite.