Flexible Wearable Strain Sensors Based On Buckled Structure

Flexible strain sensors are a kind of sensing device that when subjected to external force,the strain sensor as a whole undergoes deformation,resulting in a change in the output electrical signal.It has a wide range of application prospects in the fields of human health monitoring,medical surgery,intelligent industry,and aerospace equipment with flexible large deformation characteristics.At present,the prevailing problems of flexible strain sensors mainly include: 1)strain sensors can not simultaneously withstand low temperature(-40 ℃)and high temperature(100 ℃)environments.2)It is difficult to simultaneously achieve large deformation,high linearity,high sensitivity,and good cyclic stability.3)Strain sensors in the process of stretching release the influence of factors and scientific laws leading to the instability of the material interface has not yet been thoroughly elucidated.Aiming at the above problems,this thesis designs a flexible strain sensor based on buckled structure,proposes the synergistic effect of multiple conductive materials,and realizes the strain sensor’s large deformation,high linearity,wide temperature region,low hysteresis,and good interfacial stability by optimizing the flexible substrate material as well as regulating the material ratio,as follows:Firstly,two-dimensional lamellar Ti3C2 Tx MXene was synthesized by etching with HCl and Li F.Ti3C2 Tx MXene/graphene strain sensors based on PDMS 184 elastic substrate were designed and prepared.The buckled structure was obtained by prestretching plasma oxygen treatment.The buckled uniformity increased with increasing plasma-oxygen treatment time.The strain sensor operates in a wide temperature range(-40 °C—120 °C)with fast response(72.6 ms at-40 °C;62.7 ms at 0 °C;52.7 ms at120 °C),high sensitivity(GF=0.97 at-40 °C;GF=1.82 at 0 °C;GF=2.01 at 40 °C;GF=1.09 at 120 °C),wide detection range(1-120%)and good cycling stability.The strain sensors are capable of monitoring small deformation movements and large deformation movements of the human body in real time by fitting them on the human skin or sewing them on clothes.Next,Ti3C2 Tx MXene/carbon nanotubes(CNTs)/ fluoro-rubber flexible strain sensors based on 3M VHB elastic substrates were designed and prepared.The substrate pre-stretch-release process was used to obtain a uniformly distributed and tightly arranged buckled structure,which realized the high linearity and wide detection range(1%-150%)of the strain sensor,and the use of fluoro-rubber as an adhesive to connect the CNTs and the Ti3C2 Tx MXene solved the problems of easy disconnection of the Ti3C2 Tx MXene sheet layers during the stretching process,the poor recovery performance,and the poor elasticity.The problems of easy disconnection between the Ti3C2 Tx MXene layers during stretching,poor recovery performance,and poor elasticity were solved,enabling the strain sensor to maintain good cyclic stability,fast response time(21.2 ms),and high sensitivity(461).The Ti3C2 Tx MXene/CNTs strain sensors were applied to the monitoring of flexible deformations of the human body,and it was found that the strain sensors were able to monitor the small human body movements of the throat,as well as the larger deformational movements of the index finger,the wrist,the elbow,walking,lifting/lowering the head,and breathing in real time.Moreover,the Ti3C2 Tx MXene/CNTs/fluoro-rubber strain sensors were combined with a pneumatic soft-body robot to be able to monitor the crawling of the soft-body robot and the clamping of objects in real time.Finally,Ti3C2 Tx MXene/Ag NWs/LM self-healing strain sensors were designed and prepared.Uniformly distributed and tightly arranged buckled structures were obtained by a pre-stretch-release process on a flexible substrate,and the buckled structures increased the deformation(100%)and linearity of the strain sensor.The disulfide and hydrogen bonds in the self-healing PDMS were composited with the conductive materials Ti3C2 Tx MXene/Ag NWs and LM to produce strong interactions,which increased the stability of the interfaces and avoided positional changes between the conductive materials and the elastic substrate during the stretching process.During the stretching process,Ag NWs lapped between the Ti3C2 Tx MXene sheet layers,achieving high sensitivity(3.22).LM acted as a bridge between Ag NWs and Ti3C2 Tx MXene,reducing hysteresis(0.448%).In addition,the strain sensor had the advantages of high linearity(0.98157)and wide detection limit(1%-100%),fast response time(145ms),good cycling stability(1,000 cycles),and self-healing.The strain sensors before and after self-healing can be combined with the tail of the fish,and the strain sensors are able to monitor the swimming of the fish in the water in real time before and after self-healing.In addition,the strain sensor can be combined with an electrothermally driven soft robot,and the strain sensor is able to monitor the crawling of the soft robot before and after self-healing.In this paper,the electrical and sensing properties of the strain sensor are enhanced by controlling the morphology of the flexible strain sensor,the selection of the conductive material the interaction between the conductive material and the flexible substrate,and other strategies.A high-performance flexible strain sensor was realized,which provides a valuable reference for human health monitoring and soft robotics research.