Preparation Tand Properties Of Flexible Sensor Based On Polythiophene And Its Derivatives

Wearable sensor is an important tool for communication between people and the environment in the Internet of Things era.Sensors can convert changes in human physiological characteristics and the environment into electrical signals,which have wide applications in healthcare and artificial intelligence.With the development of intelligent electronic devices,higher requirements are placed on the sensitivity and stability of flexible sensors,and the substrates of flexible sensors are also required to be biocompatible.Polymer materials are widely used in flexible sensors.The chemical and physical properties of polymers are highly tunable,and their molecular configurations can be changed by controlling synthesis conditions,doping,etc.Currently,the research direction of flexible sensors is to improve the performance of sensors by designing functionalized polymer composites and constructing micro-nano structures of sensitive materials.In this work,functionalized composite materials are designed based on polythiophene(PT)and its derivatives poly(3,2-ethylenedioxythiophene): poly(styrene sulfonate)(PEDOT: PSS),and the micro-nano structure of the composite materials is constructed by controlling the preparation process to improve the sensing performance of sensitive materials.The flexible pressure and temperature sensors with high sensitivity,fast response,and high stability were constructed.The application potential of wearable sensors in real-time monitoring of human motion and medical-health fields is explored.To improve the reliability of sensor in the deformation process,a stretchable and easily-to-process polyurethane fiber was selected as the substrate,and the stretchable conductive polyurethane fiber was prepared by the electrodeposition of copper-catalyzed by an organic conductive polymer.Conductive polyurethane fiber was used as the electrode of the flexible sensor,and the mechanical stability and electrical integrity were studied.The main research contents and results of this dissertation are as follows:(1)Research on flexible piezoelectric pressure sensor based on polyvinylidene fluoride(PVDF)/PT composite.Using fibrous PT to induce the configuration transformation of PVDF from α phase to β phase improves the piezoelectric properties of the composites.A high-sensitivity piezoelectric pressure sensor with PVDF/PT as the sensitive material was constructed.The porous structure of the sensitive layer is beneficial to improve the sensitivity of the pressure sensor.The sensitivity of the sensor under a force of less than 0.3 N is 4.961 V/N,which shows that the sensor has obvious advantages in the detection of small pressure.Under the action of the electric field,the interface between PT and PVDF can accumulate charges and cause interface polarization,which increases the dielectric constant of the composite material and improves the polarization performance of the composite material.The reliability test shows that after 5000 external forces are continuously applied to the pressure sensor,the voltage output of the pressure sensor only drops by 2.6%,indicating that the sensor has long-term working stability.The wearable pressure sensor based on PVDF/PT can be used for real-time monitoring of human joint movement and breathing frequency,which proves that the sensor has great application potential in the field of real-time monitoring of human medical health.(2)Research on flexible temperature sensor based on PEDOT: PSS/CuPc conductive composite.The PEDOT: PSS/CuPc conductive composite was prepared as the sensitive material for a biocompatible negative temperature resistivity temperature(NTC)sensor with high resolution and fast response by spin coating.After adding CuPc with high carrier mobility to the conducting polymer PEDOT: PSS,the electrostatic interaction between PEDOT: PSS and CuPc lowers the potential barrier of electronic transitions in the composites and improves the thermoelectric properties of the composites.The packaged temperature sensor has high sensitivity,high resolution,and high stability in the range of 20～80 °C.When the temperature suddenly changes from25 °C to 50 °C,the response and recovery time of the temperature sensor are about 1 s,indicating that the sensor can be used to monitorthe temperaturreal-time time.Comparing the measurement results of the temperature sensor and the commercial infrared thermal imager on the human body represents that the test results of the sensor are accurate and reliable.The flexible temperature sensor based on PEDOT: PSS/CuPc is used to monitor the temperature and frequency of human respiration,which indicates the feasibility of the temperature sensor in continuous monitoring of human body temperature and respiration state.(3)Conductive polymer PEDOT: PSS/CuPc catalyzed copper electrodeposition to prepare stretchable conductive fabrics suitable for flexible sensors.Conductive composites were synthesized on highly elastic polyurethane fibers by in situ redox polymerization.In the process of electrodeposition,PEDOT: PSS acts as a conductive network and CuPc acts as an active site to catalyze the electrodeposition of copper,forming a structure in which the copper layer wraps the polyurethane fibers.The electrostatic interaction between PEDOT: PSS and CuPc was investigated.The mechanical and electrical properties of stretchable conductive fibers in bending and stretching were explored.The experimental results show that the electrical conductivity of the conductive fibers can reach 80% of that of bulk copper,and the dense copper crystals make the conductive fibers not easy to be oxidized.Repeated bending test and cleaning test did not change the conductivity of the conductive fiber,and the conductivity of the conductive fiber decreased by 16.8% after being stretched 1000 times at a stretch length of 6%.Therefore,conductive fibers as electrodes for wearable sensors are both biocompatible and can ensure electrical integrity under various deformations.According to the research on flexible temperature and pressure sensors and stretchable conductive fibers,a flexible pressure-temperature sensor using stretchable conductive fibers with high conductivity as electrodes was constructed.The flexible pressure-temperature sensor is attached to the inside of the mask to monitor the body temperature and the frequency and intensity of breathing at the same time,and the feasibility of applying it to real-time monitoring of portable medical health is explored.