| Hydrogels with 3D network structure show flexibility,adhesion,conductivity and biocompatibility,which was a promising substrate for flexible sensors.The excellent mechanical property was the guarantee that the hydrogel sensor would not be damaged in the application process,and the adhesion performance could ensure the accuracy of the detection signal.However,the freezing behavior of traditional hydrogels in a low temperature environment,drying behavior at high temperatures,and swelling behavior in wet environments would damage the ionic conductivity and mechanical flexibility of hydrogels,thus limiting the application of hydrogel sensors in extreme environments.Therefore,it was necessary to develop gels that can resist harsh environments(low temperature,high temperature,underwater environment)to improve the application range of gel-based sensors.In the first part of this work,K-carrageenan macromolecules were dissolved with sulfuric acid solution,and then,acrylic acid and proline were introduced.After that,a kind of viscous,stretchable and transparent low-temperature resistant hydrogel was prepared under ultraviolet irradiation.Due to the excellent adhesion properties of hydrogel,it has adhesion effect on different substrate materials(rubber,glass,wood,copper sheet).At the same time,the hydrogel also has good transparency(at room temperature,the light transmittance reaches more than 95%).Secondly,benefit from the excellent low temperature resistance,the prepared hydrogel could maintain the original mechanical properties,transparency and adhesion after being placed in an extreme environment of-35 ℃ for 24 h.Finally,after assembling the hydrogel into a sensor,the real-time monitoring of the bending movement of human fingers,wrists,knees and other joints has been successfully realized.In addition,due to the low temperature stability of the hydrogel(mechanical,adhesive,transparent),it shows potential as a strain sensor to monitor human movement in low temperature environments.In the second part of this work,acrylic acid(AA),methyl acrylamide(MAm),2-phenoxyethyl acrylate(PEA)were added to the mixed system of DMSO and ionic liquid and then,a gel with swelling resistance and high temperature resistance was obtained.The gel has good ductility,adhesion(adhesion to glass,stainless steel,plastic,rubber,paper,tomato,shell,and ceramic substrate surfaces)and excellent repeated adhesion(up to 5 repeated adhesion behaviors to metal copper sheets).The gel-based sensor has good strain sensitivity(GF=0.83),a wide sensing strain range,and reliable sensing stability(at least 600 cycles at200% strain).It could realize real-time monitoring of different joints of the human body(fingers,elbows,knees),and monitored the two opposite directions of the wrist and shoulder joints(such as the upward and downward bending of the wrist).Owing to the long-term swelling resistance and high temperature resistance(its mass remains more than 90% of the original mass after 3 days in a high temperature of 50 °C)of gel.The sensors composed of gels maintained excellent strain sensing sensitivity and stability in different solvent and high temperature environments.It could monitor the motions under 50 ℃ high temperature environment and underwater environment.The prepared gels with flexibility,adhesion,swelling resistance and high temperature resistance have a prospect in applications of sensor.In this study,a series of temperature-stabilized flexible sensors based on gel materials were prepared.These two electronic devices have certain application prospects and advantages in health monitoring and human movement.The work content of this study may provide a reference for the development of flexible sensors. |
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