Preparation And Properties Of New Polyacrylamide Hydrogel Flexible Strain Sensor

Recently years,advanced electronic devices continue to develop in the direction of flexibility and wearability,and flexible strain sensing devices have attracted wide attention because of their cutting-edge applications in human motion/health monitoring,electronic skin and robotics.Traditional strain sensor devices are mostly based on rigid materials,their stretchability and sensing performance in large strain range are poor,and they are not suitable for detecting human activities.There is an urgent need to find reliable flexible substrate materials to achieve emerging needs such as complex human motion monitoring through wearable devices integrated with flexible strain sensors.Hydrogels with hydrophilic three-dimensional cross-linked network,with a wide strain range and cyclic stability under repeated strain loading,have become ideal candidates for manufacturing flexible sensors.But traditional hydrogels have the disadvantage of limited structural adjustability.Due to the lack of effective energy dissipation mechanism,their mechanical properties are poor,which hinders their development in the field of flexible wearable.In this paper,through physical/chemical double crosslinking network and the enhanced effect of micellar crosslinking on the double network is used to realize the controllable preparation of high-performance conductive hydrogel.Hydrogel sensor with new network structure has excellent sensing performance,mechanical performance and cycle stability.In this paper,a double network structure hydrogel was successfully prepared by combining the chemical cross-linked network formed by polyacrylamide(PAM)and the physical cross-linked network formed by polyvinyl alcohol(PVA).The chemical cross-linking network of PAM is used as the basic framework to maintain the structure of the hydrogel.The synergistic effect of the chemical cross-linking network of PVA and the dual network provides a good energy dissipation mechanism for the hydrogel.And on this basis,we introduced sodium casein(SC)into the double network hydrogel system for the first time to prepare ionic conductive hydrogels with excellent performance.It is worth noting that the introduction of SC in PAM/PVA double network system produces excellent synergy effect.First,a mixed solution is prepared by 1 one-pot method as a precursor,then heat treatment is carried out at 50°C to form a hydrogel,and finally the wire is connected to the hydrogel to prepare a sensor.In this paper,two hydrogels,PAM/PVA and PAM/PVA/SC were prepared,and the effects of different compositions and ratios on the mechanical properties,sensing properties,electrical conductivity and cyclic stability of hydrogels were investigated.The results of the study are as follows: The formation of the dual network structure provided by PAM and PVA improves the strength of hydrogel hydrogen bonds,and the hydrogel has the best mechanical properties when the doping amount of PVA is 0.36 g.The interaction of the dual network provides an effective energy dissipation mechanism,so the PAM/PVA hydrogel sensor has good sensing and cycle stability.After adding SC,the micelles produced by hydrolysis can produce excellent synergistic effect with the double network structure.When the doping amount of SC is 1.0 g,PAM/PVA/SC hydrogel shows the best comprehensive mechanical properties(maximum strain is 719%,maximum stress is 444.3 k Pa),rapid self-recovery after stretching,and stability after 150 continuous cycles of stretching,this is mainly attributed to the breaking and reconstruction of dynamic hydrogen bonds in the physical cross-linked network and the sufficient energy dissipation mechanism generated by the relative motion of the dual network structure.Since SC can drive a large amount of free sodium ions,PAM/PVA/SC hydrogels can maintain high stability and good conductivity without adding additional fillers,and have good sensitivity in a relatively large range(Gauge Factor,GF = 2.17 under 400% strain).The conductive hydrogel can also accurately and stably convert physiological signals emitted from various parts of the human body into electrical signals for human movement monitoring.The combination of these excellent characteristics makes PAM/PVA/SC hydrogel have good development prospects in flexible wearable electronic devices.