Research On Preparation And Sensing Properties Of Polyvinyl Alcohol Conductive Hydrogel

With the rapid development of artificial intelligence and sensor technology,people’s demand for flexible consumer electronics has also increased.Flexible sensor is an important part of flexible electronics.The materials commonly used in flexible sensors are elastomer,foam,hydrogel,etc.Among them,hydrogel has a good fit,flexibility and high flexibility,which has attracted extensive attention in the field of wearable health monitoring,software robots,information encryption and other fields.Polyvinyl alcohol(PVA)is a widely used water-soluble material,which can form three-dimensional network hydrogel through simple freezing thawing.However,the threedimensional network inside the traditional hydrogel is unstable and has a single structure.Under the effect of external loads,it produces irreversible deformation,and can not withstand large external forces,which can not meet the standards of practical application.The basic requirement of hydrogel as a flexible sensor is that it can first closely fit the human body,and at the same time,it also needs to have certain mechanical properties,such as toughness and resilience,excellent frost resistance,moisture retention and stable conductivity.These properties have brought new requirements to the structural control of the internal three-dimensional network of hydrogel.Therefore,it is urgent to prepare a hydrogel that can meet the above requirements in order to greatly expand its application field.The aim of this paper is to improve the mechanical properties and frost resistance of hydrogel at the same time.The conductive hydrogel with freezing resistance,long-term storage and resilience was prepared by using the mixed solution of ethylene glycol and water instead of single aqueous solution.On this basis,the reinforcing agent cellulose and liquid metal were added to obtain the hydrogel with high toughness and high strength.The morphology,structure,mechanics,electricity and sensing properties of the hydrogel were tested,and its application in health monitoring,Morse code and wireless sensing were explored.The specific research contents are as follows:(1)Polyvinyl alcohol/ethylene glycol(PVA/EG)conductive hydrogel were prepared by a simple one-pot method using magnesium chloride hydrate as conductive filler and ethylene glycol/water as solvent.Choosing the content of PVA as variable,the mechanical properties,electrical properties,freezing resistance and long-term storage properties of the hydrogel were systematically studied,and a hydrogel with good resilience and flexibility was selected.A resistivity flexible pressure sensor is constructed,and NI ELVIS II+ acquisition system is used to collect the corresponding data.On the computer Lab VIEW program page,the corresponding change signals under different human motion states are displayed in real time.Even at-20℃,it also shows stable sensing performance,which lays the foundation for the subsequent conductive hydrogel with frost resistance and high sensing stability.(2)In order to make up for the lack of stability and conductivity of the polyvinyl alcohol conductive hydrogel prepared above,the polyvinyl alcohol/nano cellulose/liquid metal(PVA/CNF/LM)conductive hydrogel with good conductivity,excellent resilience and mechanical properties was improved and prepared.By adding CNF(Cellulose nano fiber)and LM(liquid metal)with hierarchical structure,the conductive hydrogel has excellent mechanical and electrical stability and excellent sensing performance.Compared with PVA/EG hydrogel,it has excellent mechanical properties(its fracture stress is 3.86 MPa,the maximum strain is 918%),high sensing stability(strain 30%,cycling 100 times),and can detect some small strains,With a wide range of strain monitoring,it can achieve real-time monitoring of external strain signals such as human movement and water droplet falling.The hydrogel also has good wave absorption performance,its electromagnetic performance reaches 34.8d B at 12 GHz,and its electromagnetic performance exceeds 20 d B at 10-18 GHz.This provides a new method for constructing flexible electronic devices with high toughness and high sensing stability.(3)The prepared polyvinyl alcohol composite conductive hydrogel is used in the field of wireless sensing.Using STM32F103 MCU as the central controller,combined with A/D module and transmission module,the signal conversion and wireless transmission of data can be carried out,the strain signal transmitted from the hydrogel end can be collected and converted into voltage signal,and the voltage signal change curve corresponding to the strain can be displayed in real time at the We Chat Mini Programs end through Bluetooth transmission,which realizes the monitoring of human motion,external strain and other signals,and has excellent stability.