Preparation Of Flexible Stress-Strain Sensors Based On Ion-Conductive Hydrogels And Their Application

In recent years,the applications of flexible sensor devices in the fields of humancomputer interaction,health monitoring and smart wearable devices have started to develop rapidly.In terms of being the active material for flexible sensors,the good flexibility and biocompatibility of hydrogel materials make hydrogels very outstanding in the preparation of flexible sensors.Hydrogels can be divided into ionic conductive hydrogels and electronic conductive hydrogels according to their different conductive fillers.Among them,electronically conductive hydrogels are mainly filled with carbon materials,conductive polymers and conductive nanomaterials,but their applications are greatly limited due to the opacity,biocompatibility and low sensitivity of these fillers at higher strains.Conductive hydrogels with ions as conductive fillers can easily be made transparent.Compared to electron-based hydrogels,ionic hydrogels will have better biocompatibility.Moreover,changing the components in the hydrogel can make the hydrogel with specific functions such as antifreeze,self-healing and self-adhesion.In this paper,two different functional hydrogels were prepared and their performance as flexible sensors was investigated.The main research and conclusions are as follows:(1)Preparation and performance analysis of freeze-resistant and highly sensitive ionconductive hydrogelsIn this chapter,Hydroxyethyl Cellulose(HEC)and polyvinyl alcohol(PVA)were used as raw materials to construct PVA hydrogel networks by co-blending and freezethawing,and ion-conductive hydrogels with different HEC contents were prepared.The results showed that when the HEC content was 1.5 wt %,the mechanical properties of the hydrogel were significantly improved,with a tensile strain at break of 340% and a maximum stress of 239 k Pa.when the hydrogel was stretched,the resistance of the hydrogel would change accordingly.In addition the ion-conductive hydrogel can be directly adhered to human skin,presenting different resistances depending on the bending angle of the knuckle,and showing stable sensing performance with repeatable real-time monitoring of strain and deformation.The hydrogel can also be formed into a selfpowered device by simple manipulation,and the self-powered device can reach a voltage of 0.839 V.The prepared hydrogel also has good freezing resistance,water retention,and mechanical properties due to the addition of dimethyl sulfoxide(DMSO).The results indicate the potential utilization of this hydrogel for flexible sensors.(2)Preparation and performance analysis of highly tensile self-adhesive conductive hydrogelsIn this chapter,with reference to the adhesion properties of mussel,a functional hydrogel with adhesion function was prepared by a two-step process using PVA,sodium alginate(SA),tannic acid(TA)and acrylic acid(AA)as raw materials.Based on the multiple weak bonds and synergistic effects among the three components in the hydrogel,the functional hydrogel has high stretchability(strain >980%),biocompatibility and adhesion properties.The functional hydrogel has a large strain detection range(10-900%)and a high sensitivity(maximum GF=16.75).At small strains(<200%)GF≈6,a value of sensitivity closer to the theoretical value of ionic hydrogels.The strain sensor can provide real-time monitoring of human finger flexion and wrist flexion and other movements,and has great potential for applications in human health monitoring,smart wearable devices and soft robots.