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SiO_2 gel / glass micro- structure formation , characterization and control

Author: ZhangYaDong
Tutor: WangMinQuan
School: Zhejiang University
Course: Materials Science
Keywords: Structure formation Polymerization rate Gel particles Hydrolytic polymerization Mesoporous structure Materials provided Gel pores Average molecular weight Gel structure The specific surface area
CLC: O648
Type: Master's thesis
Year: 2002
Downloads: 262
Quote: 7
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Abstract

The organic-inorganic composite optical functional materials with the development of information technology in the past decade has made great development, widespread concern by the international academic community. Sol-gel method as a low-temperature synthesis method due to its unique advantages, has been widely used in organic / inorganic composite. The sol-gel technology in the preparation process of the material microstructure. Application of gel chromatography, BET and infrared spectroscopy experimental methods, system pH, water silicon ratio (Ro) and organically modified tetraethylorthosilicate (TEOS) hydrolysis polymerization process, SiO: gel forming hole structures are also discussed and the methods of control. Focus on the study of the impact of the the hydrolysis polymerization rate and the relative size of the sol-average molecular weight distribution and aggregation and its associated with the the gel particle distribution and structure; organically modified the role of the gel pore structure and mechanism to obtain a batch of valuable research results provide a theoretical basis for the controlled preparation of inorganic matrix material and process control principles. PH = 2.0-4.5 range of pH values ??investigated SiO: gel pore structure. The results show that when the pH = 2.0-2.9, due to the hydrolysis rate is much larger than the rate of polymerization, the initial stage of the reaction was chain low-polymer-based, but with the increase in reaction time, the chain type polymerization increased, so that the polymer chain to the second three-dimensional network development, the micelles grow up, resulting in formation of pore size distribution 6A and 40A two most probable distribution. The same time, the gel pore volume and specific surface area increased gradually evolved from pore to pore structure. When the pH = 3.0-4.5, due to the hydrolysis rate is decreased rapidly, the polymerization rate increased, the average molecular weight increases, the main showed a higher degree of polymerization long chain polymeric molecules, micelle size is increased, but the distribution dispersion, no obvious probable distribution, so the 6A and 40A at the most probable distribution disappear, a sharp decline in the gel pore volume and specific surface area, the Central hole material into a non-porous materials. Therefore, the reasonable control of the pH value of SiO: gel pore size from microporous adjust to the hole as well as non-pore structure. Water silicon ratio Ro = ? ? ? within the gel structure. The results showed that the water silicon than change the system TEOS and H2O concentration and hydrolysis reaction rate parameters of the gel structure works. In pH when RO \With Ro increases, the average molecular weight increases, the degree of polymerization and the gel increases in size, pore volume and specific surface area is increased rapidly, Ro = 2 than the surface area of ??the maximum, and showed obvious micropore and hole may be a few distribution. With Ro's continue to increase, the increase in pore volume and a few distribution peak, and the emergence of a number of smaller aperture holes can be a few distribution. The reasonable control of the water silicon ratio adjustment control SiO: gel pore structure and an effective technical approach. Methyl, ethyl, and vinyl-modified silicon alkoxide (respectively referred to: MTES, ETES and of VTES) - Xa - the impact of the law of the the hydrolysis polymerization and gel structure. Found that organically modified group mainly affect the speed of silicon alkoxide hydrolysis polymerization and gel formation and structure works. Role of the modified base mainly depends on its electronegativity and size of the group size, electronegativity greater the greater the rate of polymerization of silicon alkoxide hydrolysis; larger the group size, the slower the rate of polymerization of silicon alkoxide hydrolysis. Microporous gel in the gel during the heat treatment and in the pore structure due to the depth of the hydrolytic polymerization, the removal of the organic solvent and the gel particles adjustment occurs regular changes. Condensate limb vitrification, microporous material is reduced, in the pore structure has been improved, and thereby provides a better environment for the organic light emitting material. Adding an organic polymer in the process of the formation of gel MMA Precursor hydrolytic polymerization process almost no effect. They are in the final gel is deposited by gel particles in the pore structure, thus increasing the connection of the Q of the gel particles to thereby improve the toughness of the gel. The microporous structure of the gel in the organic dye molecules added have not changed, they occupy a position Q in the hole of the gel particles. This porosity model has a narrow neck and wide-bodied \The above structure will we choose the sol-gel process conditions to prepare the structure of the material required to provide a theoretical basis. We can call by selecting the pioneer liquid value, water-silicon ratio, precursor type and by adding an organic polymer and an appropriate heat treatment of the gel to adjust and improve the micro-structure of the inorganic gel matrix. This will provide a good foundation for our superior preparation performance organic and inorganic composite optical functional materials, has an important meaning and application value.

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