Human Flexible Strain Sensor Based On PDMS/MWCNTs Layer-by-layer Self-assembly

With the rapid development of artificial intelligence(AI),Internet of Things(IOT)and other fields of science and technology,electronic skin(E-skin)is receiving widespread attention,since it is an important tool for connecting the world's entities and virtual networks.As a member of the E-skin system,flexible sensors are of great significance to the realization of human-machine interaction,because they have many functions such as data collection and information feedback.In the field of smart medical system,the important demand for real-time data collection makes flexible strain sensors gradually develop into a hotspot of scientific research today.Although traditional silicon-based metal sensors have excellent detection performance,their inherent rigidity limits their application in flexible E-skin system.Integrating the characteristics of biocompatibility,high sensitivity,high repeatability,fast response,simple manufacturing process,low cost,large range,etc.has always been an urgent problem in the development of flexible strain sensor.This paper aims at the demand for a large range of flexible strain sensors in the acquisition of all-round human movements.Based on the traditional and mature layer-by-layer self-assembly method,the flexible material polydimethylsiloxane(PDMS)and carbon-based conductive material multi-walled carbon nanotubes(MWCNTs)are integrated.By optimizing the manufacturing process and device's performance,a new kind of resistive PDMS/MWCNTs/PDMS flexible strain sensor was designed and prepared for the purpose of real-time monitoring of human motivation.The main research contents of this paper are as follows:(1)The electrostatically driven monomolecular layer self-assembly method is used to prepare a strain-sensitive composite film.By optimizing the ratio of PDMS main agent and curing agent,MWCNTs concentration,and self-assembly process parameters,the uneven dispersion of carbon nanotubes on the surface of the flexible substrate is solved.Besides,by doing these improvements,the sensor can also meet the mechanical and electrical performance,which are required by the strain sensing application in the skin flexible surface environment.Plus,these improvements ensure that the sensor can work effectively in a large range,too.In addition,the developed self-assembly process has the advantages of low cost and high efficiency and large area manufacturing.(2)A tensile and pressure strain automatic test system suitable for wide-range and high-precision testing was built.Detailed data on the sensor's tensile limit,tensile and strain response and other sensitive properties was obtained.In addition,some important evaluation information like sensor's sensitivity,response time and other application requirements was obtained,too.The PDMS/MWCNTs/PDMS described in this paper has a tensile strain response range of 0.1%-75%,and the resistance changes linearly during 0.1%-50%stretching with a gauge factor(GF)of?107.1.Plus,the response time is?0.28s.At the same time,the sensor response law and its mechanism under different pressures are discussed.(3)For the application of E-skin in the field of smart medical treatment,based on the concept of medical innovative service experience,a comprehensive human motion acquisition system and some preliminary application examples was designed.Under different test environments,the prepared PDMS/MWCNTs/PDMS strain sensors can effectively sense micro-scale movements such as human micro-expressions,speaking,etc.,as well as large movements such as limb and joint movements.These behaviors could reflect advantages of this type of sensor to capture different motion states and signals.These examples provide a technical idea for real-time and reliable monitoring of human vital signs.The research in this paper shows that the layer-by-layer self-assembly method can effectively prepare PDMS/MWCNTs/PDMS flexible strain sensor structures.The obtained device has an ultra-wide strain response range,which can adapt to complex limb deformation and sense movement changes,and has the potential for application in smart medical assisted diagnosis.