Structural Design Of Aramid Nanofiber Aerogel And Its Proton Donor Regulation Mechanis

Aramid nanofiber aerogel has the characteristics of light weight,high porosity,large specific surface area,excellent thermal stability and low thermal conductivity,and can be used as a high-efficiency thermal insulation material for personal protection in high-temperature environments,chemical,construction and other fields.However,the application of aramid nanofiber aerogels is severly limited due to theirlow mechanical properties.To address the above problems,we proposed a proton donor-regulating reprotonation strategy to fabricate asymmetric structured aerogel membranes and skin-core structured aerogel fibers,which contain dense and porous layers,by changing the effective concentration of proton donors;Benefitting from the synergistic effect of the composite structure,the membranes and fibers demonstrate a simultaneous improvement of mechanical properties and thermal insulation performance,providing a new method for high-performance aramid nanofiber aerogel.The main research contents and results are as follows:（1）Proton donors can control the reduction process of polyanion in aramid nanofibers,and further affect the binding form between fibers;when proton acid is used as proton donor,polyanions can be quickly reduced to form a dense structure with tightly packed fibers.However,the water as a proton donor,aramid nanofibers tend to form a porous nanofiber network structure.（2）Through the scraping membrane forming process and the proton donor regulation mechanism,under the action of the continuous coagulation bath of proton acid and water,an asymmetric structure ANFs aerogel membrane（ASAAMs）containing a dense skin layer and a porous body part is prepared.The structure can be adjusted by the concentration of the nanofiber dispersion,the type and concentration of proton acid;benefit from the advantages of the composite structure of the skin layer and body part,ASAAMs show light weight(volume density is as low as 19.2mg·cm^-3),high breaking strength（11.8 MPa,an increase of 13.5 times）,higher thermal resistance（decomposition temperature 541.5℃）,flame retardant,and efficient heat insulation(the thermal conductivity is as low as 29 m W·m^-1·K^-1)and other advantages.Furthermore,a scraping-based process is further proposed to fabric the aerogel membrane in a continuous and scalable manner,making it promising practical application in many civil and military fields.（3）By means of wet spinning and proton donor regulation mechanism,asymmetric structure ANFs aerogel fibers（ASAAFs）with a dense skin layer and a porous core layer were prepared,and the influence conditions of the skin-core structure were systematically studied.The formation of a dense skin layer improves the orientation of nanofiber molecular chains to increase the binding force between molecules,and improves the toughness of the skin layer（35.2%）and the mechanical properties of the fiber（57.2 MPa）.At the same time,its specific surface area reaches206 m²·g^-1,the thermal conductivity is as low as 42 m W·m^-1·K^-1;ASAAFs has good textile processability,and its fabrics have good application prospects in the field of thermal protection.