Preparation And Properties Of Flexible Silica Aerogel Based On Silica Sol Nucleating Agent

Silica aerogels have become one of the most widely studied aerogels due to their excellent properties such as ultra-high transparency,high specific surface area,high porosity,and ultra-low density.Due to the rigid connection of Si-O-Si inside the silica aerogels,the silica aerogels exhibit greater brittleness.This brittle structure makes the preparation process of silica aerogels complicated,the preparation cost is high and the application is difficult.Using organ silanes containing hydrophobic groups as precursors can prepare aerogels with certain flexibility.The aerogels prepared in this way have large-sized secondary particles and a thick pearl chain skeleton structure,and there is a"neck"at the junction of the secondary particles.When subjected to external force,due to the concentration of force at the"neck",it is easy to break here.Therefore,how to prepare flexible silica aerogels with more stable structures is still a problem to be solved.In this paper,several organic precursors are prepared by adding silica sol with nano-sized Si O₂ particles.The nano-particles can be used as the nucleating center of aerogel and can be polycondensation with the hydrolysate of the precursor,generating small size secondary particles of wet gel.The obtained wet gel is aged,cleaned and dried under atmospheric pressure,and the flexible silica aerogel with excellent performance is prepared.The micromorphology of aerogel was characterized by FESEM,the chemical composition of aerogel was characterized by EDS and FTIR,and the hydrophobic,mechanical and thermodynamic properties of aerogel were characterized by contact Angle measuring instrument,universal material testing machine,synchronization analyzer and thermal conductivity meter.The research results are as follows:（1）Preparation and performance research of flexible silica aerogels with dual silicon source system:using methyltriethoxysilane（MTES）and dimethyldiethoxysilan（DEDMS）as precursors,and silica sol as the form.As a nucleating agent,flexible silica aerogels were prepared by sol-gel and atmospheric pressure drying.Among them,nano-Si O₂ particles in silica sol provide a large number of nucleation sites.These nucleation sites play a role in refining the grains,avoiding the formation of"neck"weak connections between the secondary particles,improving the degree of crosslinking of the aerogel,and obtaining a flexible silica aerogel with excellent properties.The test results show that the addition of silica sol makes the secondary particles change from smooth spherical to irregular particles,and the size is also greatly reduced.The average particle size is reduced from 3.80μm to 0.36μm.The thermal stability of the aerogels has been greatly increased,and the maximum degradation rate temperature has increased from 417.2°C to 501.2°C.At the same time,compared with the dual-precursor aerogel without silica sol,the aerogel with silica sol showed better cyclic compressibility and compression recovery ability due to the increased degree of crosslinking of secondary particles.Exhibits excellent hydrophobicity and adsorption capacity for organic pollutants.（2）Preparation and performance research of flexible silica aerogels with tri silicon source system:MTES,DEDMS and phenyltriethoxysilane（PTES）,were used as precursors.After the three precursors were hydrolyzed in acidic environment,silica sol and alkaline catalyst were added,and then the wet gel was aged,cleaned and dried under atmospheric pressure to obtain flexible silica aerogel.The results show that the silica nanoparticles in the silica sol play the role of nucleating particles when an appropriate amount of silica sol is added to the three precursors.The secondary particle size of the prepared trisilicon source flexible silica aerogels is reduced from7.5μm to 0.46μm,and the aerogels skeleton structure becomes denser,which also makes the aerogels obtain excellent mechanical properties.Moreover,the trisilicon source flexible silica aerogel has excellent hydrophobic properties,and its contact angle is 153°,which is a superhydrophobic material.This aerogel can adsorb a variety of organic pollutants and has good adsorption properties.The addition of silica sol does not prevent the hydrolysate of PTES from coating on the surface of secondary particles,and the prepared aerogel has good flame-retardant properties.（3）Preparation and performance research of flexible silica aerogels composites:Flexible silica aerogels glass fiber mat/cloth composites were prepared by impregnating glass fiber mat/cloth with flexible silica sol.Due to the good mechanical properties and hydrophobic and lipophilic properties of the flexible silica aerogels,the prepared composite material can be applied in the fields of thermal insulation and oil-water separation.In addition to this impregnation method,aerogel composites were prepared through sticking,coating,and cladding.These composite methods are simple and feasible,provide a reference for the practical application of flexible aerogels.In this paper,by adding silica sol to the preparation of flexible silica aerogel with organ silane as the precursor,the original microstructure of the aerogel was changed and the aerogel with better mechanical properties was obtained.In addition,several applications of flexible silica aerogels are explored,which provides a reference for the industrialization of flexible silica aerogels.