Preparation Of Aramid/BN Reinforcedself-healable Nanocomposites And Their Performance

Flexible electronics that can be bent, stretched and conformed to intricate surfaces are emerging as disruptive technology in numerous applications such as wearable electronics, implantable sensors and alternative energy devices. Polymers are preferred dielectric materials owing to their ease of processing, tunable dielectric constants, low cost and good film forming ability. The functional materials used in flexible dielectric devices, however, are susceptible to mechanical deformationinduced damage, resulting in loss of functionality that seriously limits device reliability and lifetime. Herein, we describe a supramolecular approach to self-healable dielectric polymer nanocomposites that are mechanically robust and capable of restoring simultaneously structural, electrical, dielectric and thermal transport properties after multiple fractures.Boron nitride nanosheets(BNNSs) with hexaganol symmetric structure were prepared via chemical solvent ultrasonic exfoliation method. The effects of ultrasonic time, centrifugal time and rate during the preparation process on the BNNSs size and thickness were studied. Oxidizer di-tert-butylperoxide(TBP), "piranha solution" H2O2/H2SO4 and silane coupling agent 1-[3-(trimethoxysilyl)propy]urea(TMSPU) were used to modify the surface of BNNSs by covalent chemical method, respectively. The tert-butoxy-functionalized BNNSs-TB, hydroxyl-functionalized BNNSs-OH and amide-functionalized BNNSs-CONH2 were obtained. Then the microstructure of these nanosheets were compared and the graft density of amide groups on BNNSs-CONH2 was calculated. Fuctionalization processes make BNNSs surface more active, which contribute to the further polymerization reaction and better dispersion in composite.Based on the Leibler’s self-healing polymer system, we designed and synthesized a novel self-healable dielectirc nanocomposite by introducing BNNSsCONH2 into polyer matrix instead of urea compoent via in situ m ethod. With the incorporation of surface-functionalized boron nitride nanosheets, the polymer nanocomposites exhibit many desirable features as dielectric materials such as higher breakdown strength, larger electrical resistivity, improved thermal conducti vity, greater mechanical strength, and more stabilized dielectric properties when compared to the pristine polymer. It was found that the recovery condition remained as the same during sequential cycles of cutting and healing, therefore suggesting no aging of the polymer nanocomposites with mechanical breakdown. Moreover, moisture has a minimal effect on the healing and dielectric properties of the polymer nanocomposites, which is in stark contrast to what is typically observed in the hydrogen-bonded supramolecular structures.In order to further improve the dielectric properties and mechanical strength of boron nitride reinforced self-healing nanocomposites, indigenous aramid modified by high energy mutual irradiation grafting was introduced into the above nanocomposite. The effects of irradiation medium and irradiation dose on three different indigenous aramid fiber(IAF3, IAF3 A and IAF12) surface performance were investigated. After comparing their surface morphology, surface element component, contact an gles with deionized water and diiodomethane and surface free energy, we chose the aramid IAF3 irradiated at 200 k Gy as an organic reinforcement and further cut and fuctionalized it with dopamine to nake it compatible for self-healing nanocomposites system. The mechanical strength and dielectric properties of aramid/BNNSs self-healable nanocomposite were studied and the results showed th at organic aramid particles have a little influence on the dielectric constant and dielectric loss of composite, while the electric breakdown strength and the tensile Young’s modulus were improved obviously. Based on the electromechanical model theory, the relations between Young’s modulus, dielectric constant and the theoretical breakdown strength of composites were established. Analysis within the framework of the electromechanical model highlights the significance of the excellent mechanical strength of BNNSs for improving the breakdown strength of dielectric polymers and composites.This work extends the application scope of self-healable supramolecular materials from conductive units to insulations and expands the material landscape available to flexible electronics and energy devices. We envision the integration of self-healing capability can significantly enhance functional materials longevity when they serve under harsh conditions such as frequent high voltage arcing, repeated mechanical distortions, and abrupt temperature changes.