Preparation Of Aerogel Based On Methyltrimethoxysilane Precursor By Ambient Pressure Drying Process

Aerogel is a kind of porous amorphous solid material composed of nanoscale particles with three-dimensional network structure.Due to its controllable structure and characteristics of low density,high porosity,and high specific surface area,aerogel has been widely used in the fields of electricity,heat,acoustics and biomedicine.Silica aerogel is one of the most representative aerogel materials.Traditional silica aerogel is prepared by sol-gel method and supercritical drying technology.Although supercritical drying technology can protect the three-dimensional porous network structure of aerogel from collapse,the large-scale production of aerogel is largely limited by the high requirements of this technology for equipment.Therefore,how to prepare complete bulk aerogel with excellent performance by atmospheric drying technology has become one of the important directions in related research fields.The capillary pressure will be generated during the process of atmospheric drying of silica wet gels,which will destroy the gel skeleton.In order to obtain low-density aerogel with uniform and complete pores,solvent replacement,drying control chemical additives,and surface modification are usually used to improve the gel properties.This paper uses the sol-gel two-step method,methyltrimethoxysilyl(MTMS)as the precursor,by the hydrophobic solvent pre-built in the gel framework,due to the hydrophobic solvent boiling point is low,in the atmospheric drying process gasification compensates the part of the wet gel pore by solvent evaporation generated by the capillary force,this process does not require complex solvent replacement and surface modification measures,etc.In the process of atmospheric drying,the capillary shrinkage was reduced and the preparation period was shortened.The organic silica aerogel with high porosity,low density and uniform pore distribution was prepared.1.Microencapsulation behavior of hydrophobic solvent.The hydrophobic solvent was dispersed into small oil droplets under the action of high-speed stirring,and the long chain alkyl trimethoxysilane and MTMS were used as co-precursors to hydrolyze and condense at the oil-water interface to form organosilica-coated hydrophobic solvent microcapsules.The effects of different reaction conditions,alkyl chain length of long chain alkyl trimethoxysilane,amount of hydrophobic solvent and different sample addition methods on the morphology and particle size of silicone hydrophobic solvent microcapsules were explored.The results showed that:(1)The microcapsules treated by ultrasound at 25 ℃ had a more uniform particle size.(2)The particle size of the microcapsules prepared by alkyl silane precursor with different chain lengths was analyzed.The longer the alkyl chain,the larger the particle size of the microcapsules.(3)The wall thickness of the microcapsules prepared with long-chain alkyl trimethoxysilane as the precursor is too thin to coat the hydrophobic solvent well,so it needs to cocondensation with MTMS to form a complete shell.(4)The addition of co-stabilizer hexadecane(HD)was conducive to the preparation of organosilicon hydrophobic solvent microcapsules with uniform dispersion and uniform particle size.2.The microencapsulated hydrophobic solvent was introduced into the MTMS hydrolysate and the aerogel was prepared by atmospheric drying.Hydrophobic solvent microcapsules with different particle sizes were introduced into MTMS gels prepared under different conditions.It was found that the introduction of hydrophobic solvent microcapsules could effectively reduce the capillary force contraction and prepare a complete bulk aerogel.However,when the particle size of the introduced microcapsules was much larger than the gel pores,the effect of reducing capillary force could not be effectively played.The degree of fracture of the material is high.3.Organosilica aerogel composed of hollow organosilicon particles was prepared by hydrophobic solvent microcapsules using MTMS as precursor.The effects of different stirring methods,reaction temperature,hydrophobic solvent types and silane types on the physical properties,microstructure,hydrophobicity and mechanical properties of silica aerogels were studied.Depending on the preparation conditions,the density of the aerogel after atmospheric drying was 0.0659-0.1571 g·cm-3,and all of them were hydrophobic.The contact Angle was in the range of 129 °-158 °.4.Mechanical properties of organic silica aerogel.The results showed that the mechanical strength of the prepared organosilica aerogel could be improved by the introduction of hydrophobic solvent microcapsules,but the effect was weakened when the particle size of the introduced microcapsules was large.