Fabrication And Performance Study Of Highly Sensitive Flexible Piezoresistive Sensors Based On Controllable Interface Structures

Owing to the excellent sensing performance,stable repeatability and facile manufacture,flexible piezoresistive sensors have numerous practical applications in smart wear,electronic devices,healthcare and etc.,herein,attracting increased attention of researchers in recent years.With the continuous development of flexible piezoresistive sensors,the piezoresistive sensing composites prepared by one kind of fillers and traditional sandwich structure gradually tend to be saturated,which are difficult to meet the further needs of improving sensors’performance.Therefore,it’s particularly important to explore the role of multiple conductive fillers and interface structure design in enhancing piezoresistive sensor’s performance.This work aimed at constructing piezoresistive sensors with excellent comprehensive sensing performance and convenient fabrication process.Thus,a series of piezoresistive composites were prepared by applying thermoplastic polyurethane（TPU）as the flexible matrix,and using poly（3,4-ethylene-dioxythiophene）:poly（styrene-sulfonate）（PEDOT:PSS）and carbon nanotubes（CNTs）as two kinds of conductive fillers.At the same time,different regular interface structures were introduced to improve the sensing performance.In addition,the properties like electrical properties,compressive mechanical properties,piezoresistive sensing properties and practical applications of as-prepared sensors were systematically studied.The main research contents and results of this work are as follows:（1）Fabrication and conductive/sensing performance of composite films with double conductive filles:Flexible composite films were fabricated through solution blending with TPU as matrix,PEDOT:PSS and CNTs as conductive components.The results showed that composite films with double fillers displayed better electrical performance than that with single filler.And when the ratio of PEDOT:PSS to CNTs was 1:3,the composite film exhibited relatively better comprehensive sensing performance,including high sensitivity(-0.093 k Pa^-1,0～2.5 k Pa),broad sensing range（0～50 k Pa）,fast response（0.18 s）,and stable repeatability（in800 cyclic compression times）.（2）Fabrication and performance of composite films with fabric texture interface:Superficially structured fabric-like films were fabricated through using stainless steel fabric as template and polydimethylsiloxane（PDMS）as inverse template.Testing results indicated that superficially structured film had higher piezoresistive sensitivity than plain film,and double layered film sensor had higher sensitivity than sensor with single layer.Among them,the double layered twill-like sensor showed high sensitivity(-0.068 k Pa^-1),wide sensing range（0～70 k Pa）,fast response time（0.27 s）,and excellent repeatability（in 1000 cyclic compression times）.Moreover,although better dispersion of fillers made electrical properties more stable,the sensitivity was reduced due to the more difficultly broken conductive network.（3）Fabrication and performance of composite films with corrugated interface structure:Double layered film sensors with corrugated structure were constructed via using corrugated acrylic plate served as template and polydimethylsiloxane（PDMS）as inverse template,and assembling two structured layers at different angles.As a result,the five kinds of double-layer film sensors exhibited positive piezoresistive effect under the initial pressure,and then changed to negative piezoresistive effect with pressure increased.Furthermore,different assembling angles made great influence on sensors’performance.Such as bump-bump assembled sensor showed excellent negative piezoresistive performance(-0.121 k Pa^-1)while 30°crossed sensor had outstanding positive piezoresistive sensing ability(0.164 k Pa^-1),and both of which displayed stable repeatability（in 1000 cyclic compression times）.（4）Applications of superficially structured composite film sensor:The superficially structured piezoresistive sensors were respectively applied in speech recognition,physiological signal monitoring,human behavior detection and etc.The results showed that there were regular correspondences between the resistance change and detected signals/behaviors,verifying their promising application potentials in many fields.In summary,based on double conductive fillers of PEDOT:PSS and CNTs,and combined with different interface structure design,this work fabricated a kind of highly sensitive composite materials.The improved electrical properties were attributed to the cooperation of the two kinds of fillers;and the increased sensitivity was related to the introduction of regular interface structure;in addition,the different assembling angles also accounted for the enhanced sensing properties;and at last,structured piezoresistive sensors were proved to have a promising application prospect.Therefore,the work of this paper could provide a feasible idea for the research and development of novel piezoresistive sensors with higher sensitivity,and also provide a reference for the practical applications of piezoresistive sensors.