Design,Assembly And Sensing Application Of PVA Hydrogel And Eutectic Gel Based Flexible Strain Sensors

Flexible strain sensor is a kind of sensor that can convert mechanical signals into electrical signals.Because of its high flexibility,good flexibility and small size,it has attracted much attention.It has broad application prospects in electronic skin,biomimetic materials,soft robots and health monitoring.The original performance of the hydrogel-based flexible strain sensor has been greatly improved by the addition of two-dimensional nano fillers and a variety of different properties have been obtained.The research and application of hydrogel flexible strain sensor is still in its infancy and there are still many key scientific problems waiting to be solved.For example,the stability of some two-dimensional nano-filler is poor,which reduces the service life of the material;Hydrogels lack the ability to self-heal,which limits their application,and the material lacks the ability to adhere to the skin.In this paper,the green and environmentally friendly PVA material is first used as the polymer framework,MXene is introduced to improve the mechanical properties and electrical conductivity of the material,and the surface of MXene is wrapped with polyanionic salt CMC to achieve the effect of oxidation resistance.The dynamic boron-ester bond between boron ion and hydroxyl group is introduced into the system,so that the material can obtain the ability of self-healing.Moreover,the material shows excellent adhesion ability with various materials.The sensing performance and sensing application of hydrogel-based flexible strain sensor are studied.Subsequently,in order to solve the problems of hydrogel material,such as easy to lose water and easy to crystallize at low temperature,which greatly limited its use conditions.In the following work,we used eutectic solvent to replace the water in the hydrogel,which not only obtained multi-environmental stability,but also extended the service life of the material because the passivation ability of the eutectic solvent protected MXene from oxidation.In addition,natural substance silk fibroin（SF）was introduced as the strengthening material to improve the mechanical properties.At the same time,dynamic boron ester bond was introduced to make the material acquire self-healing ability.The main research contents and results of this paper are summarized as follows:1.Self-healing,adhesive,and antioxidant MXene-reinforced conductive hydrogels for stain sensorWe developed a dynamic self-healing hydrogel system based on boron-ester bond and realized the antioxidant protection of MXene against sodium carboxymethyl cellulose（CMC）polyanion salts.The main chain of polyvinyl alcohol（PVA,P）and polyacrylic acid（PAA,P）was crosslinked,and MXene（MCB）modified by CMC and borate was used as nano filler.The hydrogel of PPMCB could heal automatically within 6h.As CMC edges MXene,it avoids the disadvantage of easy oxidation of MXene.This excellent antioxidant property ensures that the hydrogel retains more than 90%mechanical properties and sensing capability after 45 days of oxidation treatment.In addition,hydrogels have strong adhesion to different materials.Based on these unique features of the PPMCB,flexible sensors with self-healing and long-term durability can be assembled.This study provides a new strategy for preparing self-healing conductive MXene hydrogels that can be used in flexible wearable devices.2.MXene multifunctional conductive eutectic gel with self-healing,cold resistance,drought resistance and oxidation resistanceAccording to the previous study,the problem of freezing water at low temperature and volatilizing water at high temperature exists in the hydrogel-based flexible strain sensor.Therefore,water was replaced by eutectic solvent（DES）with excellent environmental stability,and e-Ti₃C₂T_x was prepared by MXene intercalation DES method using PVA as polymer network,enhanced by silk fibroin（SF）and MXene.The problem of easy oxidation of Ti₃C₂T_x was solved by introducing dynamic covalent bonds.A superelastic self-healing eutectic gel was designed and prepared.The non-covalent crosslinking effect of SF and 2D nanosheets makes the prepared eutectic gels have super elasticity and strength.The tensile strength of the prepared eutectic copolymer is 7.63 MPa and the elongation at break is 1115.2%,which is higher than most polymers（<1000%）.In addition,the eutectic gel assembled sensor has a high ionic conductivity of 0.61 S/m and a high strain sensitivity of 5.17k Pa-1.In addition,eutectic also showed excellent self-healing ability,with rapid self-healing within 10 minutes.Tensile strength is restored to 84.7%,elongation at break is restored to 97.4%,and stable electrical signals can be transmitted after 200 cycles at 30%strain.