Preparation Of Conductive Double Network Hydrogel And Its Application In Flexible Sensors

Recently,flexible sensors have attracted wide attentions due to the ability of converting external stimuli into electrical signals,which showed applications in the fields of artificial intelligence,soft robots,health monitoring and so on.However,the conventional flexible sensors cannot meet their applications in soft robots and flexible electronic devices due to their small detection ranges and low sensitivity.Double-network(DN)hydrogels are composed of two cross-linked networks with strong asymmetric structure.And the mechanical properties of the DN hydrogels can be improved by regulating the interaction and structure of the two networks.Therefore,alginate nanofibril/graphene oxide/polyacrylamide nanocomposite hydrogel and agar/sodium chloride/polyacrylamide hydrogel sensors were prepared,respectively.A series of research work has been carried out to improve the mechanical properties and electrical conductivity of the hydrogel flexible sensors.1.The conductive DN hydrogels were fabricated as wearable flexible sensors by adding graphene oxide into a DN hydrogel containing alginate nanofibril network and polyacrylamide network.The hydrogels exhibited outstanding mechanical properties,such as superior strechability(3370%),improved tensile strength(0.54 MPa),and high compressive strength(4.4 MPa).The hydrogel temperature sensor showed a high temperature sensitivity of 2.0%/°C in the temperature range of 25-65 °C and has a good stability.Additionally,the hydrogel strain sensor exhibited a high GF of 4.2 at a tensile strain of 2000%.And the strain sensor could be applied at a small strain of 0.02% at a low voltage of 0.5 V.The strain sensor also demonstrated a fast response time(? 0.25 s)and long-time stability.Therefore,the strain sensor can monitor both large limb movements and subtle muscle movements of the human body.2.Inspired from the human skin,the ionic conductive DN hydrogel was prepared using agar,sodium chloride and acrylamide as raw materials.The physically linked agar network acted as the first network,and the chemically linked polyacrylamide network served as the second network.The two networks had a strong entanglement and interpenetration with each other,contributing to the high mechanical properties of the hydrogels.The obtained hydrogels have a wide range of unique features,such as high transparency,superior tensile strength(400 kPa),high compression strength(2.7 MPa)and good stretchability(1920%).Moreover,thanks to the thermoreversible sol-gel properties of agar,the pregel can be for the hydrogels,resulting in a high strain sensitivity with GF of 2.1.The hydrogels also demonstrated excellent sensing stability.Furthermore,the hydrogel showed an extremely broad of strain sensitivity window(0.5%-1600%)and a low operating voltage of 0.08 V.Based on these outstanding properties,the hydrogel sensor could quickly and accurately monitor both tiny and large motions of human body.