Preparation And Properties Of Polymer Flexible Strain Sensors

The rapid development of wearable smart devices,electronic skin and other flexible electronics has contributed to the flexibility demand for smart strain sensors.However,traditional strain sensors made of rigid materials such as silicon and metal exhibit poor flexibility,stretchability,and sensitivity,and thus restricting their application in the field of flexible electronics to some extent.In order to develop the strain sensors with merits of flexibility,stretchability,and wearability,the flexible strain sensors based on polymers have emerged and become one of the emerging research hotspots in the field of polymer composites.Although many advances have been made in the research of polymer-based flexible strain sensors,there are still some bottlenecks for the strain sensors to be resolved,such as cumbersome preparation processes,poor transparency,and contradiction between high strain sensitivity and wide strain response range,which hinder their practical application in the fields of electronic skin,human health monitoring,wearable smart devices and so on.In this dissertation,the methods of adjusting the conductive network and designing the structure of the conductive layer are utilized to improve the strain sensitivity and repeatability,enhance the light transmission of the material,and then continuously improve the comprehensive performance of the polymer-based flexible strain sensors.Details of the research contents and the results are summarized as follows:1.Preparation of a filled-type carbon black/carbon nanotubes/isoprene rubber strain sensor and its properties:zero dimensional(0D)carbon black(CB),one-dimensional(1D)carbon nanotubes(CNTs)and hybrid conductive particles CNTs/CB are filled into isoprene rubber(IR)to generate the flexible strain sensors by a two-roll mill.The dependence of the electromechanical properties of the strain sensor on filler dimensionality and structure of conductive networks is systematically investigated.It is found that CB/IR composites display ultrahigh strain sensitivity and good repeatability since CB-networks are easily broken under stretching and fast rebuilt under releasing.However,the drawback of CB/IR composites is the high electrical percolation threshold(8.01 phr),leading to the complex processing,poor mechanical properties,and high cost.In contrast,CNTs/IR composites possess low percolation threshold(1.44 phr)but also low sensitivity and poor repeatability because CNT-networks are more stable under strain.Interestingly,it is observed that combining 0D CB and 1D CNTs to construct the hybrid CNT-CB networks is an effective route to overcome the drawbacks of CB-networks and CNT-networks,which endows the flexible CNTs/CB/IR composites with low percolation threshold,high strain sensitivity and good repeatability.Moreover,the demonstration experiments show that the flexible CNTs/CB/IR composite could be used to detect human motions and emotional expressions,which can be used as the flexible strain sensor in human motion monitoring and other fields.2.Preparation of a transparent strain sensor based on the sandwich-like composite containing an ultrathin conductive CNT layer and its properties:a simple spray deposition and transfer method is reported to fabricate a polydimethylsiloxane(PDMS)-based transparent strain sensor with an ultra-thin conductive layer(tens of nanometers).The fabricated strain sensors exhibit superb stretchability,good optical transparency,and excellent sensing performances,which can detect both the subtle and large strains with outstanding stability and repeatability.It is found that with the increase of CNTs content,the electrical property and strain response range of PDMS/CNTs/PDMS composites increase,but the light transmission performance decreases.The strain sensor based on the PDMS/CNTs/PDMS composite containing 0.16 mg/cm2 CNTs on the conductive layer presents a good optical transmittance of 53.1%at 550 nm,broad sensing range of over 130%.Furthermore,the composite possesses the ability to monitor both the subtle motions of facial expressions and the large motions of human joints,which has great potential applications in human motion detection,wearable electronics,and electronic skin.3.Preparation of a sandwich-like strain sensor with a dual conductive layer structure and its properties:we fabricate a sandwich-like polymer based flexible strain sensor with high strain sensitivity and wide response range by designing a dual conductive layer structure containing both flexible conductive layer of CNT-PDMS and brittle conductive layer of CNT-silane coupling agent(KH550).The dependence of the electromechanical properties of the strain sensor on the component proportion and the thickness of CNT-KH550 conductive layer is systematically investigated.It is found that the introduction of an ultra-sensitive conductive layer of CNTs/KH550(1/5)can significantly enhance the strain sensitivity of the strain sensor while maintaining the advantage of a wide strain response range.Furthermore,the sensitivity and repeatability of the polymer-based flexible strain sensor with the dual conductive layer structure are improved as the thickness of CNT-KH550 conductive layer increases.In addition,this type of polymer-based flexible strain sensor exhibits good durability and the ability to monitor human pulse,throat and joint motion,which endows the strain sensor with broad application prospects in human health monitoring,human motion monitoring and other fields.