The Preparation And Properties Of TPU-based Flexible Sensing Materials

With the rapid development of electronic skins and wearable electronic devices,the flexible sensing materials as the vital components of these devices,become one of the emerging research hotspots for both academy and industry.Conductive polymer composites composed of conductive materials and polymers have great application value in the field of flexible sensors,owing to their numerous superiorities of stretchability,light weight,corrosion resistance and good processability.In order to meet the various application requirements of flexible sensors in the fields of electronic skins and wearable electronic devices,such as healthcare monitoring,intelligent robotics,and environmental monitoring,flexible sensing materials based on polymers have received tremendous attention.However,there are still some bottlenecks for flexible sensing materials based on conductive polymer composites to be resolved.For example,in terms of flexible temperature sensing materials,it is difficult to prepare the flexible temperature sensing materials with monotonic linear response to temperature;for the flexible pressure sensing materials,it is hard to fabricate the flexible pressure sensing materials with good air permeability,easy machining and mass production.To solve the above problems,flexible thermoplastic polyurethane（TPU）-based sensing materials with different macroscopic shapes are designed by the selection of functional fillers and structural design of the sensor in this thesis.The main research results and conclusions are discussed as follows:（1）Preparation and properties of highly flexible TPU/single-walled carbon nanotube（SWCNT）composite-based temperature sensing materials with linear negative temperature coefficient effect and photo-thermal effect.We prepare a flexible TPU/SWCNT complex film by a facile method of solution blending,ultrasound-assisted and the following thermal annealing.Thermal annealing is beneficial to improve the conductivity of TPU/SWCNT complex films.As the thermal annealing time is increased,the conductivity of the complex films increases at first and then remains almost unchanged.Therefore,the thermal annealing time of 2 h is sufficient to greatly increase its conductivity.The TPU/SWCNT complex films with different content of SWCNT exhibit a linear negative temperature coefficient effect.With the increase of SWCNT content,the temperature sensitivity of complex films is decreased.Besides,the complex films have obvious photo-thermal effect.As the content of SWCNT is increased,the photo-thermal effect of composite films is enhanced.What is more,the complex films can not only monitor the deep/normal respiration,but also have the capabilities in non-contact thermo-sensation,indicating great potential in electronic skins.（2）Preparation and properties of multifunctional iontronic sensor based on liquid metal-filled hollow ionogel fibers.Hollow and porous TPU@ionic liquid（IL）ionogel fibers are fabricated by successive coaxial wet-spinning,freeze drying and ultrasonic immersing in sequence.Liquid metal-filled hollow ionogel fibers are prepared by injecting the LM into the hollow TPU@IL ionogel fibers and sealing the end.The effects of different IL and LM content on the pressure sensing performance of LM-filled hollow ionogel fiber-based sensing materials are studied.With the increase of IL content,the pressure sensitivity of the fiber-based sensing materials is improved.With the increase of LM content,the pressure sensitivity of the fiber-based sensing materials is enhanced and then decreased.When the LM content is 75 vol%,the pressure sensitivity is highest.The optimized fiber-based sensing materials exhibit a high detection resolution（1.16 Pa）,a high sensitivity(13.30 k Pa^-1),a wide detection range（0-207 k Pa）,and fast response/relaxation time（9.9 ms/14.8 ms）.Besides,the fiber-based sensing materials also have a capacitive response to temperature stimulus.As a fiber-based temperature sensing material,it exhibits a high resolution（0.02°C）,high temperature sensitivity(25.99%°C^-1),good repeatability and reliability.Due to the excellent pressure/temperature sensing properties,the ionogel fiber-based iontronic sensor is able to not only detect weak psychological signals of human pulse,the extent of the wrist bend but also simulate Morse code for information transmission.The sensor can also work as a touchless sensor to sense the proximity of the palm,edged tools,ice,and fire.A simple fiber grid made of LM-filled coaxial TPU@IL ionogel fibers is designed to detect both the position and magnitude of applied force,as well as the shape of the loaded object,exhibiting great potential in wearable electronics and healthcare monitoring.