Preparation And Sensing Performance Of Flexible Graphene Nanocomposites With Configurated Porous Structure

Flexible nanocomposites have received continuous attention in the field of piezoresistive strain sensors due to their excellent sensing properties and good ductility.The main applications include smart wearable electronics,structural health monitoring,human-computer interaction,and other fields.However,flexible sensors currently face crucial problems which include low sensitivity,low effective linear range and poor stability.By exploiting strategies of material selection,structure configuration and sensing performance optimization,the design of a tunable conductive network becomes the current development direction for the research and application of flexible strain sensors.In this work,three aspects are mainly conducted,including material selection optimization,porous structure design,and sensing performance improvement,to investigate the effect of configurated porous structure on the sensing performance of flexible graphene nanocomposites.Firstly,a conductive network with segregated structure is designed to explore the influence of filler concentration and porous structure design on the flexible nanocomposites sensing performance.A sacrificial template method is used to prepare porous structured graphene nanosheet/polydimethylsiloxane(GNP/PDMS)composites,where a green templating agent is taken with GNP conductive filler to form the segregated microstructure to achieve the improved sensitivity,linear range and failure stress.The results show that for the enhancement of sensitivity and linear range,the graphene nanoplate/polydimethylsiloxane(GNP/PDMS)composite with a mass fraction of 4wt% GNP exhibits the best sensing performance.Furthermore,the porous structured GNP/PDMS composites indicate a permeation threshold of 2wt%,while the solid structured GNP/PDMS composites demonstrate a permeation threshold larger than4wt%,showing the significantly reduced permeation threshold of the conductive filler GNP in porous structured composites.This is due to the stacking sequence of GNP with ordered microstructure by forming a stable segregated conductive network under the stimulus of an applied strain.The porous PDA@HNT/r GO/PDMS sensor composite was prepared by using ice crystal as template by introducing one-dimensional halloysite nanotubes(HNT)to further resolve the problems of poor stability and low tensile strength of the strain sensor.The sensitivity of the sensor is regulated by controlling the concentration of r GO.The porous graphene aerogel(GA)sensor shows the characteristics of light weight,low density,and high porosity.With the decrease of GO concentration,the sensitivity of the sensor increases.However,its mechanical properties and stability decreases due to the increase of internally formed pores.On this basis,by setting varied HNT: r GO concentration ratios(0:1,1:8,1:6,1:4,1:2,1:1),we determine the optional GA performance,and effectively improve the stability of the sensor as well as increase the effective linear range.This is because the introduction of HNT can construct the internal structure of crosslinking.In addition,by coating the HNT surface with polydopamine(PDA),the binding strength between HNT and matrix can be further enhanced,thus the performance of the sensor is relatively stable.Finally,to further improve the ductility of the strain sensor,a threedimensional(3D)dual conductive network structure is constructed by carbonization and impregnation of organic precursor,and the effects of carbonization temperature of the organic precursor and GNP solution concentration on the sensing performance of porous structured composites are investigated.With melamine foam being carbonized under 400℃,500℃ and 600℃,respectively,the 3D structure of porous carbon foam with skeleton is dipped into different concentrations of GNP solution(1wt%～3wt%),to build the dual conductive network structure with both conductive fillers,to eventually achieve GNP/C/PDMS composites with desirable sensing performance.