Study On Atmospheric Pressure Prepartion Of Silicone Aerogels And Their Reinforcement

An aerogel is a solid material obtained by replacing the liquid solvent in a wet gel with air while keeping the network structure of the gel as unchanged as possible.Aerogels have many excellent properties,including extremely low density,high porosity,low thermal conductivity and high specific surface area,making them applicable in thermal,electrical,optical and acoustic applications.In this thesis,methyltrimethoxysilane(MTMS)with hydrophobic methyl group was used as the precursor to prepare silicone aerogels.The monolithic silicone aerogel materials were prepared by solid substrate powder decomposition and this method is simple and easy to use,and it is suitable for large-scale preparation of highly porous aerogel materials,and the hydrophobicity is also studied.Solvents were pre-embedded in the sol of MTMS to prepare silicone aerogels,and the factors affecting the aerogel properties were investigated.A silicone aerogel material was prepared by using a solid matrix decomposition method using methyltrimethoxysilane(MTMS)as the precursor.Micron-sized ammonium carbonate particles were compacted in a Buchner funnel and then wetted with polymethylsilsesquioxane(PMSQ)solution by filtration.After solidification of PMSQ at ambient temperature,the ammonium carbonate decomposed at atmospheric pressure by heating,remaining PMSQ skeleton to achieve an aerogel-like porous material.The effects of the concentration of PMSQ solution,the particle size of ammonium carbonate particles and the surface treatment method of ammonium carbonate on the performance of the aerogels were studied.The applicability of this method to silicone rubber was also studied.It was found that the density of aerogel materials increases with the concentration of PMSQ.When the concentration of PMSQ solution is 20 wt%,the particle size of ammonium carbonate particles is 50?m,and the solution of ammonium carbonate particles is treated by 1wt%stearic acid,the surface modified aerogel has good performance,with the density 0.093g/cm~3,the porosity 95%,the volume shrinkage 12.6%.The water droplets can roll on the surface of the sample without leaving traces,and the water contact angle reached 153°.Its oil collection capacity for oil layer on the water surface reached up to 10g vacuum oil per1g aerogel sample..The silicone aerogel was also prepared by a two-step acid-base catalyzed process using methyltrimethoxysilane(MTMS)as the precursor.To the aqueous system of the acid-catalyzed methyltrimethoxysilane hydrolyzate,a hydrophobic organic solvent cyclohexane insoluble in the aqueous phase was added,and the MTMS hydrolyzate wass adsorbed on the surface of the cyclohexane doplets to make cyclohexane exist in the form of the microcapsules and pre-embedded in the gel.The condensed MTMS hydrolyzate forms a gel skeleton,resulting in a monolithic aerogel consisting of hollow microspheres.The effect of cyclohexane content and alcohol-water ratio on the aerogel properties was studied.When the cyclohexane content was 15 ml and the alcohol:water=1:1,the aerogel performance was the best,leading to the aerogel with density of 0.088 g/cm~3,the porosity 95.4%,and the volume shrinkage 22.3%.The effect of the surfactant cetyltrimethylammonium bromide(CTAB)on the aerogel properties was investigated.The results show that the surfactant can effectively enhance the stability of the emulsion,reduce the interfacial tension between cyclohexane and water,and effectively help the aerogel to form.When the surfactant CTAB content is 0.26 wt%,the cyclohexane is 5 mL,an aerogel having good morphology and integrity can be obtained.The density,volume shrinkage,and porosity of the obtained aerogel are 0.104 g/cm~3,23.2%,and 94.5%,respectively.The aerogel has a good appearance and is smooth and crack-free.The effects of adding aminopropyltrimethoxysilane(APS)and attapulgite nanofibers on the mechanical properties of silicone aerogels were investigated.The results show that aminopropyltrimethoxysilane can effectively enhance the compactness of the aerogel network backbone and enhance the compressive capacity of the aerogel.The compressive capacity of the aerogel increased from 15N to80-85N with the addition of APS.The effect of the content of the attapulgite nanofibers in the aerogel on the elastic strain of the silicone aerogel shows a trend of increasing first and then decreasing,and when the content of the attapulgite fibers is too much,the attapulgite fibers cannot be dispersed in the aerogel network,resulting in the inability to form a complete intact aerogel.Attapulgite nanofiber-reinforced aerogel was prepared by the sol-gel method.When the content of the attapulgite fiber was 1 wt%,the silicone,the compressive properties of aerogels can reach 40-45N,and the mechanical properties of aerogels are significantly enhanced.