The Preparation And Property Characterization Of Flexible Aerogel And Aerogel Composites On SiO₂ Substrate

SiO2 aerogel is a novel material composed of fine particles and has extremely low density,ultra-high porosity and specific surface area.Therefore,aerogel has broad research prospects in the fields of heat,acoustics,optics and energy.Due to its specific nanopore size and network structure,aerogels exhibit small size effects and interfacial effects which is the unique properties of nanomaterials.However in engineering applications,conventional rigid aerogel materials are difficult to be used on profiled structures and flexible members because of its fragility.At the same time,the hygroscopicity of conventional aerogel makes it easy to fail in some adverse environments,and it is difficult for the aerogel to serve universally and for a long time.In this paper,a resilience-resistant hydrophobic SiO2 aerogel was prepared by using a silicone source,and nanofiber prepared by electrospinning was used as a reinforcing phase to develop the novel flexible aerogel composite.In this paper the silica flexible aerogel was prepared by sol-gel method,then the gel was placed in an ethanol solution for replacement,aged for a sufficient period of time.Finally the gel was placed in a supercritical kettle to remove the solvent to obtain a complete SiO2 flexible aerogel.Since the process parameters such as solid content and amount of alkali catalyst have a significant influence on the growth and aggregation of particles during the gel process.The microstructure,mechanical properties,thermal properties and hydrophobic properties of the samples with different process parameters were characterized.The changes rules of various aspects were analyzed and explained.The final aerogel present low density(?0.092g/cm3),low thermal conductivity[?0.0338W/(m·K)],excellent hydrophobicity(the contact angle is about 145.6°),certain strength(the Young's modulus is about 75KPa)and outstanding compression elastic rebound characteristic(can be compressed as 50%as its original length and recovered back completely).Meanwhile the failure temperature was about 350? which was measured by thermal gravity analysis experiment.In order to the overall performance of aerogel material further,to prepare fiber composite aerogel material is a simple and effective way.The type of reinforcing phase doped with aerogel has a great influence on the performance of the final composite.Due to the traditional ceramic fiber's brittleness property,the fiber will destroy the aerogel excellent flexibility as a reinforcing phase.Therefore,using nanofibers with better flexibility as the reinforcing phase can improve the mechanical properties of the aerogel while avoiding the damage of the fiber to the aerogel skeleton.The polyvinylbutyra(PVB)which was used as organic template was mixed with SiO2/SnO2 sol solution,then the nanofiber was fabricated by stretching the mixed solution in the high voltage electrostatic field.The fiber diameter was adjusted by organic matter concentration,electric field intensity,feed speed and molar ratio of Si to Sn,and the change law of fiber morphology we re analyzed and explained.Then the nanofiber with diameter of 320nm and uniform morphology was prepared and the size distribution of nanofiber was determined by statistics.To study the influence of nanofibers on the composites further,the effect of nanofibers doped with different mass fractions on the structure and properties was investigated.The mechanics property decreased first and then increased with the increase of fiber content,meanwhile the pore size distribution of aerogel was optimized and the thermal conductivity decreased obviously because of the addition of nanofiber.When the fiber content was 5wt%,the mechanic property of the aerogel increase obviously and the compression-resilience property was not impaired.The SiO2 aerogels and composites prepared in this paper have high flexibility,hydrophobicity,and extremely low thermal conductivity.Therefore,it is expected to be applied in the heat insulation and heat preservation of deformed structure under complicated environment,such as the coated insulating material of heat transfer pipe or the interlayer of mountaineering thermal insulation suit.