Design,Preparation And Application Of Multifunctional Conductive Hydrogel In Flexible Strain Sensor

As a new type of soft material,conductive hydrogels(CHs)combine the superior characteristics of conductive materials and hydrogel three-dimensional networks,and have broad application prospects in the fields of electronic skin,soft robots,flexible sensors,and wearable electronic devices.The current problems are mainly concentrated in two aspects: 1.In the process of preparing hydrogels,chemical cross-linking or physical cross-linking is usually used,which leads to uneven internal network structure of the material,which affects the stability and service life of the sensor;2.As nanofillers tend to aggregate and randomly distributed in the polymer matrix,it is necessary to functionalize its surface or use a large amount of fillers to form a continuous conductive network,but it will weaken the mechanical properties of CHs.In addition,the introduction of adhesion,self-healing,and anti-swelling properties into the conductive hydrogel is expected to further expand the application fields of sensor devices.Based on this,this paper focuses on the network structure design,performance characterization and sensor application of high-performance CHs-based composites.The main research content and research are summarized as follows:(1)In view of the instability of the CHs network structure,using Poly(N-isopropylacrylamide)(PNIPAM)as the base material,poly(3,4-ethylenedioxythiophene):polystyrene sulfonic acid(PEDOT:PSS)as the conductive filler,graphene oxide as the physical crosslinking agent,and a very small amount of N,N'-methylenebis(acrylamide)(BIS)as the chemical crosslinking agent,an interpenetrating network structure is formed through PNIPAM and PSS to prepare a series of GO/PEDOT:PSS/PNIPAM hydrogel(GPP-h).The effect of the content of PEDOT:PSS on the mechanical properties and electrical conductivity of the hydrogel was studied,and its sensing properties and chemical stability were discussed.Studies have shown that the mechanical properties and electrical conductivity of GPP-h show an increasing trend with the increase of the concentration of PEDOT:PSS.At the same time,GPP-h also exhibits excellent fatigue resistance and fast response time.The rate of change of its resistance is closely related to the strain received,which initially realizes real-time monitoring of human motion signals.In addition,due to the sparse chemical cross-linking of small molecules and the introduction of GO,the hydrogel also has excellent chemical stability.Specifically,it has been immersed in strong acids and polar solvents for more than 400 days,and it can still maintain the stability of the structure.And the hydrogel sensor can stably detect mechanical strain signals in corrosive solvents.GPP-h also has excellent adhesion and can be adhered to the surface of many objects(shape,material),which is very important for human body applications.This work provides great potential for the application of flexible sensors in different solvent environments,and is expected to expand the application range of hydrogel-based flexible electronic materials.(2)On the basis of the previous chapter,this chapter uses the new two-dimensional MXene material as the conductive and reinforcing filler of the hydrogel,which can further reduce the types of components in the material system to save costs.In addition,due to the lack of adhesion of most hydrogels,additional tape is required to bond the hydrogel to the solid surface,which may cause slippage or delamination,thereby detecting a malfunction signal.Inspired by "bricks" and "mud",the MXene/PDA composite was successfully synthesized by in-situ polymerization of dopamine(DA)on MXene nanosheets through a one-step process.By incorporating PDA/MXene nanosheets into the hydrogel network to prepare MXene nanocomposite conductive hydrogel(MNCH),the prepared MNCH has excellent self-adhesion,high tensile fracture rate and excellent flexibility.It is further assembled into an MNCH-based flexible strain sensor to detect human physiological activities,with fast response time,wide strain sensing range,high sensitivity and excellent fatigue resistance.This work paves the way for the manufacture of wearable,highly sensitive,and wide-sensing flexible strain sensors.The sensor can have broad application prospects in many applications such as the next generation of artificial electronic skin,personal medical care monitoring and human-computer interaction.