Research On Cellulose-based Composite Electrolyte Humidity Sensors

The electronic humidity sensor has received widely attention by the advantages of the small size and easy integration.Whether for the detection and control of environmental humidity,or the monitoring of human breathing state and skin humidity,the sensitivity,stability and biocompatibility of humidity sensors were required higher demands.As a kind of environmental friendly materials,cellulose has been widely used in the preparation of humidity sensors due to its large specific surface area and hydrophilic properties.However,the structure modification of the cellulose itself is difficult,resulting in the undesirable sensitivity of native cellulose-based humidity sensor.To solve this problem,this paper has carried out research work on the design and preparation of moisture-sensitive materials,fabrication of the sensor,the testing of device sensitivity performance,the analysis of moisture-sensing mechanism and the applications of device.The main research contents include:1.To solve the problem of the unsatisfactory sensitivity of native cellulose-based humidity sensors,moisture-sensitive membranes were prepared by compounding a hydrophilic ionic liquid(1-butyl-3-methylimidazolium chloride([BMIM]Cl))with cellulose nanofibers(CNFs).The device showed a high response(27.95 p F/% RH)in a wide humidity range(11%–95% relative humidity(RH)),which is more than four times of native cellulose-based humidity sensor.And the response and recovery time were 43 s and 1 s,respectively.The moisture-sensitive mechanism in different humidity environments of the sensor was investigated using equivalent circuit analysis and quartz crystal microbalance device.Finally,the applications of the sensor in the fields such as human breathing and fingertip moisture monitoring were explored.2.In order to avoid the limitations of rigid materials in application,filter paper,as a kind of flexible cellulose materials,was selected.For the problem of the flexible sensors that the sensitive materials and electrodes tend to separate from the substrate during the bending process,deep eutectic solvent(DES)was selected as the sensitive material,then dispersed it inside the cellulose paper and polymerized it by UV irradiation.Self-supporting sensitive film obtained can be tested directly.The self-supporting sensor has a significantly higher sensitivity to humidity compared to native cellulose paper,the response at 95% RH increased from 25.9 to 5513.2.Subsequently,the moisture sensing mechanism of the sensor was analyzed using complex impedance spectrograms and equivalent circuits analytical methods.Poly-DES(PDES)formed conductive pathways inside the cellulose paper,enhancing the conductivity of the material after water absorption.Meanwhile,the effect of different bending degrees on the device was investigated.The self-supporting sensor was stable at curvature radius of 8 mm,5 mm,3 mm,with almost no shift in response values.For the problem of unsatisfactory sensitivity of native cellulose-based humidity sensor,a composite sensitive system of cellulose compound electrolyte was constructed and the humidity sensors with high sensitivities were prepared,and for different application scenarios,a self-supporting flexible humidity sensor was designed.The above researches provide a new idea for high performance cellulose-based humidity sensors.