Rapid Preparation And Toughening Modification Of SiO₂ Aerogels

Silica aerogels are the most highly porous nanostructured materials,with a three-dimensional network of silica particles,and have a low bulk density,small pore size,low index of refraction,high optical transmission,extremely high porosity and large surface area.Due to their superiorcharacteristics above,silica aerogels have great potential in the field of high technology industry.However,the synthesis process of silica aerogels still needs further research,the preparation wastes most time and high cost and the product performance cannot meet the requirements,etc.The sample has large brittleness and poor mechanical properties.In this paper,silica sol/tetraethyl orthosilicate?TEOS?mixed silicon source and methyltriethoxysilane?MTES?were used as precursors.Silica aerogels were quickly prepared by using ambient pressure drying which shortened the preparation cycle.The toughening modification of silica aerogels and the influence of preparation parameters on the physical properties of aerogel was systematically discussed.The results showed that the silica aerogels were prepared by soxhlet solvent displacement and modified by three methyl silane?TMCS?after atmospheric pressure drying with silica sol/tetraethyl orthosilicate mixed silica source as precursor.Silica aerogel spheres were continuously prepared by dropping the precursor on a hydrophobic vibrating surface under ambient pressure drying.Gel time of the system can be controlled within 30 min.The apparent density is0.152⁰.186 g/cm³ and the specific surface area is 387⁴81 m²/g.The sample has a continuous porous network structure and excellent hydrophobicity.When the SiO₂mass fraction is 3%,the water contact angle of 155°.Hydrophobic silica aerogels were prepared by atmospheric drying with methyl-triethoxy silane as precursors without solvent replacement and hydrophobic modification.Their density was 0.0527 cm³/g and the thermal conductivity of MTES based silica aerogels was 0.04591⁰.04828 W/mK.The hydrophobic contact angle of the sample at room temperature is 123°.MTES based silica aerogels have good thermal stability.The total weight loss of the silica aerogel is about 11.5%at room temperature⁹00?.The pore structure shows that MTES based silica aerogels are a typical micro mesoporous material.The results of toughening modification of silica aerogels showed that the gel time of the hydroxy-terminated polydimethylsiloxane?PDMS?-OH??toughened modified silica sol/tetraethyl orthosilicate mixed silica aerogels system is not more than 30 min,and the density of the toughened aerogel is 0.186 to 0.256 g/cm³.A certain amount of PDMS?-OH?can significantly improve the hydrophobicity of the aerogel.When the mass ratio of PDMS?-OH?/silica sol is 0.125,the hydrophobic angle of the aerogel reaches 154.1°.In the sol-gel process of PDMS?-OH?toughened MTES-based silica aerogel,the gel time of the system is as short as 3 min,when the mass ratio of PDMS?-OH?/MTES is 0.1,the sample density is as low as0.05 g/cm³.