The lightweight graphene assembly film with excellent electrical conductivity and stable chemical properties is used as the sensing functional material of the flexible sensor,which can not only meet the application requirements of flexible sensors,but also effectively solve the problems of high stiffness,easy corrosion and large quality in traditional metal sensors.However,the existing conventional preparation methods of graphene assembled films generally have problems such as low efficiency and inability to large-scale preparation.The prepared graphene assemble films are poor in terms of conductivity and compactness,and are difficult to be used as ideal materials in the field of flexible sensing.In view of the above problems,this paper studies the ultra-fast and large-area preparation process of macroscopic graphene assembly films,and synthesizes high-conductivity flexible graphene assembly films with negative Poisson’s ratio.The mechanical properties and microscopic mechanism of graphene assemble films under different processes,and their application in flexible sensors are explored.The main results are as follows:(1)Ultrafast assembly of GO/NMOF-Co films is achieved by implanting superhydrophilic cobalt-based metal-organic framework nanosheets(NMOF-Co)as an additional water channel into the interlayer of graphene oxide(GO).The vacuum filtration assembly time of GO/NMOF-Co film is only 18 seconds at the fastest,which is more than 30,000 times faster than the assembly time(154 hours)of pure GO film under the same conditions.It breaks through the limitation of the thickness of the GO film prepared by vacuum filtration,and realizes the ultra-wide adjustment of the thickness of the GO/NMOF-Co film from nanometers to centimeters.In view of the problem that the preparation area of GO film is limited by the suction filtration container,the coating method is used to realize the large-area preparation of graphene assembled film,and the area can reach 170 mm×150 mm.(2)By introducing NMOF-Co nanosheets,increasing the hydrogen bond concentration inside the graphene assembled film and enhancing theπ-πconjugation,the tensile strength and strain energy density of the GO/NMOF-Co film can reach over three times that of the pure GO film.By adjusting the precursor size and heat treatment temperature,the key factors affecting the tensile mechanical properties of the large-area GO assembly films prepared by the coating method were studied.The experimental results show that under the same other conditions,when the GO sheet diameter is 3.82μm,the prepared GO assembled film without heat treatment has the highest tensile strength and strain energy density.(3)A non-contact full-field 3D strain measurement system was used to test and analyze the negative Poisson’s ratio properties of graphene-assembled films,and a reconstruction model based on X-ray tomography images to characterize the stretching of macroscopic graphene-assembled films was successfully constructed.The relationship between the negative Poisson’s ratio and the internal micropore size was studied by finite element numerical simulation,and the precursor size and heat treatment temperature were designed based on this model.A wide range of Poisson’s ratio adjustment for graphene-assembled films is achieved,and the lowest Poisson’s ratio is close to the lower limit of-1.(4)Focus on the performance of piezoelectric sensors based on graphene assembled films with negative Poisson’s ratio.The piezoelectric sensor with negative Poisson’s ratio will expand in both horizontal and vertical directions at the same time when stretched,improving the response sensitivity.The GF value of the prepared piezoelectric sensor is as high as 1512.6 in the linear range.Since the electrical conductivity of the assembled film is as high as 105S m-1,it is used as a sensing material for flexible sensors with a power as low as~4.7μW and exhibits good thermal stability.Graphene assembled films can be applied to ultra-low-power sensors that detect airflow and sound vibrations.In addition,the performance of resistive sensors based on ultrafast assembled RGO/NMOF-Co aerogels and graphene assembled films was also initially explored.The sensitivity of the RGO/NMOF-Co load sensor in the load range of 6.3~10 k Pa is-10.4 k Pa-1,which is higher than the sensitivity of the same type sensors reported in the literature in this load range.This work provides a new idea for fabricating flexible sensors with ultra-low power consumption and high performance. |