Fabrication Of Carbon-Based Flexible Composites And Their Strain Sensing Performance

As a new type of strain sensor,wearable sensor has attracted increasing attention in recent years due to its possible applications in many fields,such as signal monitoring,robot intelligent equipment,portable motion detector.In order to meet the requirement for practical application,the key materials should meet the following requirements;(1)high sensitivity for high resolution detection under small deformation;(2)high stretchability for working in large strain deformation;(3)high stability for long-term and repeatable utilization.However,it is still challenging to produce high performance sensor with both good stretchability and high sensitivity using conventional stiff materials such as metals or semiconductors.The key to develop flexible strain wearable sensors is to create flexible conductive materials with high sensitive response.Advanced carbon materials possess the advantages of high conductivity,high physical and chemical stability,excellent mechanical properties and biocompatibility,etc.In addition,their surface is easy to be functionalized and combined with further a variety of materials.Therefore,carbon materials may be used for the preparation of flexible wearable strain sensors.In this work,several carbon materials including graphene nanosheets,graphene nanoribbons,fabric derived carbon were rationally integrated together for the construction of wearable strain sensors with high performance.(1)Construction of covalent bonded graphene foam with superb electromechanical properties as elastic conductor and pressure sensor.We reported a simple fabrication of covalently cross-linked graphene foam(CCGF)by C-N bonds with superb electromechanical properties.Benefiting from the formation of covalent bonds and removal of oxygen-containing groups,the as-obtained CCGFs exhibit an excellent compressibility and conductivity.More importantly,the CCGFs exhibit tunable conductivity at different compressed strains and ultrasensitive stress responsivity(0.046 kPa"1 in the regime of 3.5-5 kPa),featuring huge prospects for elastic conductive and ultrasensitive sensing applications.The proposed strategy may enlighten the fabrication of novel materials via cross-linking for other related applications.(2)Constrution of flexible and ultrasensitive fabric-based carbon composites sensor for detecting human motions.Linen fabric derived carbon(LDC)is integrated with 2D graphene and 1D silver nano wires(AgNWs)by surface modification strategy.Owing to the unique woven structures matrix of fabric and high conductivity of silver nanowires and r-GO,the AgNWs/graphene/linen derived carbon(Ag/GLDC)composite sensors simultaneously exhibit excellent stretchability(>60%),good cycle stability,as well as high sensitivity(gauge factor of 11.2,36.8 and 74.5 in strain of 0%-20%,20%-40%,40%-60%,respectively).The composite sensors with remarkable performance were successfully used to monitor the vigorous motion of human body joints(wrist,knee joint and elbow),suggesting potential applications in human motion detection.Our work provided a new pathway for the creation of flexible and wearable composite strain sensors with high performance.(3)Construction of graphene nanoribbons/polyimide flexible wearable pressure sensors based on layer-by-layer assembly strategy.Water-soluble polyimide was composed with graphene oxide nanoribbons to give rise to an ultrathin film by using rotary coating and layer by layer assembly method.AgNWs were supported on the surface of graphene nanoribbons/polyimide(GNRs/PI)film to form AgNWs/GNRs/Pl nanocomposites.We demonstrated that the combination of AgNWs and GNRs/PI could achieve a pressure sensor with high sensitivity and high flexibility.The sensors can still maintain good stability after 3000 compression cycles.The composite sensors with remarkable performance can be successfully applied to measure the fingers bend,human pulse,throat vibration during speaking,etc.It can detect the weak movements of the body quickly and sensitively.The graphene nanoribbon-based flexible stress sensors have broad application prospect in the wearable electronic devices,biomechanical systems and other related areas.