Preparation Of Self-healing Hydrogels And Their Application In The Field Of Flexible Strain Sensor

Flexible electronic devices have attracted the attention of scientists because they could be widely employed in the field of health monitoring equipment,flexible energy storage equipment,flexible circuit boards and flexible displays.Until now,flexible electronic devices are mainly divided into two categories:flexible electronic devices based on elastomer and flexible electronic device based on hydrogels.These two types of electronic devices with different substrates have obvious advantages and disadvantages.Electronic devices based on elastomers possess high modulus,high elasticity and good resistance to mechanical fatigue,but elastomers cannot withstand large deformations,which greatly limits their further development.After years of research and exploration on hydrogel materials,researchers endow hydrogel materials with high mechanical properties and adhesion properties.These two points provide a good basis for the application of hydrogels in electronic devices.Good mechanical properties ensure that the hydrogel material remains intact under external force,while the adhesive properties could make it adhere to the skin,closely.In addition,the hydrogel can also be endued with self-healing properties to prolong the service life of electronic devices and reduce their maintenance costs.The problem that the hydrogel cannot cope with the extreme cold environment in the application is also effectively solved by introducing a multi-solvent or a high-concentration inorganic salt.In the existence of above properties,the hydrogel electronic devices have a wider range of applications.Therefore,we integrate the above properties and prepare self-healing conductive hydrogels with adhesion and tough behavior for application in the field of flexible electronic devices.In the first work,a stretchable,self-healing and conductive hydrogel is prepared via physical crosslinking including hydrogen bonding,hydrophobic association and complexation effect,endowing the hydrogels with stretchability of 1150%,tensile strength of 112 kPa,flexibility and puncture resistance.Besides,the hydrogels possess extraordinary conductive property with a conductivity of 0.0720 S cm^-1 and exhibit stable changes of resistance signals with a gauge factor of 2.506.Meanwhile,the hydrogels also exhibit adhesive performance due to the presence of catechol groups,and the maximum peeling adhesive strength could reach 23 N m^-1.It is envisioned that the highly stretchable,self-healable,adhesive and conductive hydrogels would widen the application as the flexible strain sensors for soft robots,artificial limb,movement-monitoring equipment.In the second part,a self-healing hydrogel with,mechanical,adhesive and conductive properties have been designed and prepared by introducing polydopamine nanoparticles and water-soluble ionic liquids into hydrophobic association polyacrylamide.The resultant hydrogel samples could be employed as electrolyte and wearable strain sensor,simultaneously.As hydrogel electrolytes,the resultant supercapacitor possesses capacitance of 0.37 F g^-1 and capacitance retention of 75.42%after 8000 cyclic charge-discharge tests.Furthermore,the supercapacitor exhibits capacitance of 0.365 F g^-1 after self-healing,which is 98.65%comparing to the original data.As flexible strain sensors,the hydrogels could detect tiny and large scale human movements in accordance with resistive signals with gauge factor of 0.841.It could be anticipated that the self-healing hydrogels could be prospective flexible materials for new generation of flexible sensors and supercapacitors.In the third part of the work,Li₂SO₄ was used to prepare anti-freezing hydrogels.The preparation process of the hydrogel is simple.And the obtained hydrogel possesses high stretchability,ductility,adhesion,conductivity,and self-healing properties.Thus,this hydrogel was applied into a wearable strain sensor.As a sensor,the gauge factor is up to21.12.In addition,this hydrogel-based sensor could response to the movement speed and angle of human joints rapidly.It can even collect signals of small scale movements such as speaking,smile,frown and etc.Therefore,it could be predicted that this kind of simple preparation,anti-freezing,adhesive,self-healing and conductive hydrogel could provide new design ideas for wearable electronic devices and expand its application range.In this paper,a series of flexible electronic devices,including wearable flexible sensors and supercapacitors,are prepared with hydrogel materials as the main body.These two electronic devices have certain application prospects and advantages in the field of health monitoring and energy storage.It is envisioned that this paper promotes the development of flexible electronic devices.