The Performance Research And Application Of Humidity Sensor Based On Poly(Ionic Liquid)s

The detection of environmental humidity is closely related to human life.As a measuring tool,humidity sensor is widely used in meteorological research,industry,agriculture and forestry,medical health and other fields.With the rapid development of social economy,people also pay more attention to their health and life comfort,meanwhile put forward higher requirements to the sensitivity and response speed of humidity sensor.Nowadays,although polymer,metal oxide and mixture humidity sensor are widely used as humidity materials,there are problems such as poor response,stability,durability,interchangeability,and even environmental pollution.Poly(ionic liquid)s,composed of cations and anions entirely,is a novel humidity material.In addition,it has both the properties of polymer and electrolyte.In our work,we used poly(ionic liquid)s as humidity materials to develop a kind of biocompatible humidity sensor which possesses those performance including high sensitivity,fast response,super long-term stability.We chose PIL-Br,PIL-BF4 and PIL-TFSI as humidity materials,then explore the effect of the film thickness and anion type of poly(ionic liquid)s on humidity performance.Further,the sensing mechanism of poly(ionic liquid)s was analyzed and studied,and further explained by the free volume theory greatly.Based on this,we designed the membrane structure of poly(ionic liquid)s to obtain the humidity sensor with the best comprehensive performance,and applied it in practical field.The details are as follows:At first,we investigated the effect of the film thickness and anion type of poly(ionic liquid)s on humidity performance,then studied the sensing mechanism and put forward methods to design the structure of poly(ionic liquid)s film for the optimal performance.PIL-Br was synthesized by radical homopolymerization,then PIL-BF4 and PIL-TFSI were synthesized by anion exchange method.Those were characterized by NMR and IR spectra.The humidity sensors with different film thicknesses were prepared by controlling the concentration and volume of poly(ionic liquid)s sol,the rotational speed and time of glue coater,finally the humidity performance was tested.The results showed that the sensitivity of humidity sensor increases with the increase of film thickness,It is found that PIL-Br has the best performance,followed by PIL-BF4 and PIL-TFSI by comparing the comprehensive performances.Furthermore,the free volume theory can be used to explain the sensing mechanism of the humidity sensors.In our work,the PIL-Br-10 humidity sensor has the best performance and more advantages in practical application.It possesses high sensitivity(1190),small hysteresis(3.2%),fast response/recovery(6s/10s)and excellent stability within 60 days.Furthermore,the PIL-Br-10 humidity sensor can be used for real-time monitoring of human respiration due to its high sensitivity and fast response.The results showed that the sensor can capture the change of humidity in human respiratory airflow.In addition,the PIL-Br-10 humidity sensor was combined with the DC test system to realize the portability of the sensor for detecting human skin humidity.The experimental results showed that the PIL-Br-10 humidity sensor can detect the change of humidity in different parts of human skin effectively,possessing excellent stability for two months.In the future,poly(ionic liquid)s are expected to have better application prospects in medical and health fields.