Structural Regulation And Performance Of Breathable And Flexible Ionogel-based Sensing Materials

Wearable strain and temperature sensors are desired for human-machine interfaces,health monitoring,and human motion monitoring.As the main component of wearable strain/temperature sensors,flexible sensing materials have become a research hotspot in the material field.At present,the most widely studied flexible sensing material is the flexible conductive polymer composite（FCPC）,which is composed of metal/carbon conductive filler and flexible polymer matrix.However,the poor compatibility between the metal/carbon conductive filler and the polymer matrix as well as the disordered conductive networks formed by the conductive filler in the polymer matrix lead to the poor stability and repeatability of the FCPC-based sensor under external stimuli.In addition,most of the FCPC-based sensing materials reported previously have poor air permeability,which will cause poor human comfort when they are used as wearable devices.Furthermore,the sweat produced by human skin can not be volatilized in time,which will also affect the stability of the device.In order to solve the above problems,the ionic liquid（IL）,1-ethyl-3-methylimidazolium bis（trifluoromethylsulfonyl）imide（[EMIM][NTf₂]）,is used as the sensing component,and the thermoplastic polyurethane（TPU）is used as the elastic matrix.Through electrospinning technology and wet spinning technology,the ionogel-based breathable and flexible strain/temperature sensing materials with uniform dispersion of conductive components,good stability and repeatability of stimulus response signals are obtained in this thesis.Specific research contents are as follows:（1）Preparation and performance of breathable and flexible strain/temperature sensor based on IL/TPU ionogel nanofiber membrane.The IL/TPU fibrous mat with aligned nanofibers is prepared by electrospinning technique.The fibrous mat is loaded with electrodes along the direction parallel to the orientation of the nanofibers to obtain a multifunctional breathable sensor based on an ion-conducting mechanism.As a strain sensor,the obtained sensor exhibits a wide strain working range（0～200%）,a short response and recovery time（119 ms）,a low detection limit（0.1%）,and good repeatability.In addition,owing to the negative temperature coefficient effect of the IL/TPU fibrous mat,the sensor also exhibits excellent temperature sensing performance,including monotonic temperature response,high sensitivity(2.75%℃^-1),high accuracy（0.1℃）,fast response（2.46 s）and excellent stability.This sensor can not only monitor tiny and intense human motions but also detect respiration and proximity,exhibiting enormous potential in wearable electronics.（2）Preparation and performance of strain sensor and strain-insensitive temperature sensor based on IL/TPU ionogel fiber.An intelligent ionogel fiber-based strain sensor composed of TPU and IL is prepared by wet spinning technology,which can serve as a wearable strain sensor with good linearity（a correlation coefficient of0.997）in an ultrawide sensing range（up to 700%）,ultralow detection limit（0.05%）,fast response（173 ms）and recovery（120 ms）,and excellent reproducibility.The as-prepared sensor can be used to monitor subtle physiological activities and intense joint movement of the human.More importantly,a wearable strain-insensitive temperature sensor can be obtained from the ionogel fiber if it is designed into an“S”shape,which can effectively eliminate the interference of strain on temperature sense.It is found that the inaccuracy of temperature sense is within 0.15℃ when the sensor is subjected to30%tensile strain simultaneously.Moreover,the strain-insensitive temperature sensor with an ultrahigh detecting accuracy of 0.1℃,can be used to monitor thermal radiation,proximity and respiration,exhibiting enormous potential in wearable electronic products,multifunctional electronic skin,and human health monitoring.