Preparation Of Conductive Polymer Hydrogels And Their Application Research In Wearable Sensors

In recent years,with the continuous advancement and development of intelligent technology,a variety of smart wearable sensing devices that can track the wearer's body movement,temperature,blood sugar,heart rate and other daily activities and physiological health are emerging.Hydrogel is a soft material with a structure similar to natural biological tissue.It is soft,stretchable and has good biocompatibility.Therefore,hydrogels have received extensive attention as carriers for next-generation flexible wearable devices.However,traditional chemically cross-linked hydrogels usually have poor mechanical properties and lack comprehensive properties such as adhesion and self-healing,which will not meet the needs of wearable devices.Based on the above problems,this thesis developes a variety of high-strength,anti-fatigue,self-healing,self-adhesive,conductive and multi-functional hydrogels,and conducts a detailed study on their application as flexible sensors.The specific research is divided into following parts:First,in this part of the work,a core-shell hybrid latex particles?HLPs?physically cross-linked hydrogel was prepared,in which acrylamide?AAm?and dodecyl methacrylate?LMA?were used as monomers,and silica-polybutyl acrylate?SiO₂-g-PBA?HLPs were hydrophobic association centers.Under external force,the HLPs physically cross-linked network could dissipate a lot of energy through destruction and reorganization,thereby giving the hydrogel excellent mechanical properties,such as low modulus,high stretchability,and rapid self-recovery.In addition,the addition of LiCl made the hydrogel have excellent conductivity,and the conductivity could change rapidly with the change of deformation.The sensor based on this hydrogel showed high sensitivity?5.44?,fast response time?151 ms?and recovery time?73 ms?in a wide strain range of 0.25-2000%.Based on its excellent mechanical properties and sensing performance,the hydrogel sensor could accurately monitor various human movements,including speaking,breathing,joint bending,walking and jumping,showing its potential prospects in the fields of human activity and physiological health monitoring.Second,on the basis of the work in the previous part,Ca²⁺cross-linked alginate was added as the second network to produce a tough,fatigue-resistant and strain-sensitive conductive double physically cross-linked double network?DN?hydrogel.The mechanism of high mechanical strength of hydrogels was studied through cyclic tensile tests,and it was proved that the double network structure played an important role in the reinforcement of hydrogels.When the hydrogel was stretched,the double physical cross-linked structure could dissipate energy more effectively.The obtained hydrogel had significantly enhanced mechanical properties.The fracture stress was 935 kPa,the fracture strain was 2422%,and the toughness was 10075 kJ/m³,which were more conducive to the long-term application of hydrogel.More importantly,on the one hand,the introduction of Ca²⁺could enhance the mechanical properties of the hydrogel,while at the same time,it provided excellent conductivity for the hydrogel.Hydrogel-based sensors could be used to monitor human activities in real time and repeatedly,including the movement of wrists,elbows,necks and knees,and subtle human activities such as speaking and breathing.Third,most hydrogels lack self-adhesiveness and require additional tape to bond the hydrogel to the solid surface,which inevitably causes friction and affects the actual application effect.In this part of the work,a flexible,self-adhesive,self-healing and conductive hydrogel was designed and prepared.First,the hydrophobic monomer lauryl methacrylate?LMA?was introduced to form a hydrophobically associated cross-linked network?HPAAm?with the acrylamide monomer through micellar radical polymerization.At the same time,chitosan?CS?and carboxyl-functionalized multi-wall carbon nanotubes?c-MWCNT?were introduced to form HPAAm/CS-c-MWCNT hybrid cross-linked hydrogel through electrostatic interaction and hydrogen bonding.The hybrid cross-linked network had excellent self-healing ability,and the hydrogel also showed rapid self-healing efficiency,which would effectively extend the service life of the hydrogel and give it reusability.In addition,hydrogels could interact with the surface of solid materials through?-?stacking,cation-?,and hydrophobic interactions,making the hydrogel perform repeatable self-adhesive properties to various materials?including plastic,glass,rubber,metal,and pigskin?.When the hydrogel was used as a wearable strain sensor,it could closely adhere to the skin and other interfaces to achieve fast and accurate monitoring of human movement and important physiological signals.Fourth,although conductive hydrogels have been proven to be widely used in wearable sensing devices,traditional hydrogel sensors can only be used within a limited temperature range due to freeze or evaporation of under extreme conditions,that seriously affects their practical application.In this part of the work,using acrylic acid?AA?,chitosan?CS?,graphene oxide?GO?as the main body,FeCl₃ as the ionic cross-linking point,and water-glycerin mixed solvent instead of pure water solvent,the hydrogel based ionic cross-linking and hydrogen bonding was prepared.The strong hydrogen bonding between water and glycerin keept the water molecules firmly fixed in the hydrogel network,prevented the water in the hydrogel from freezing and volatilization,and effectively improved the long-term stability of the hydrogel.Even after being placed at-20?C for 24 h,the hydrogel could still maintain good flexibility and conductivity.After being left at room temperature for 7 days,the hydrogel also maintained good stretchability and electrical conductivity,which significantly improved the durability of the hydrogel.In addition,the physical cross-linking network had rapid recoverability,while improving the mechanical properties,it also made the hydrogel have rapid self-healing,which could effectively extend the service life of the hydrogel sensor in practical applications.In this paper,from the perspective of network structure design,a series of hydrogel-based strain sensors with comprehensive properties such as flexibility,stretchability,viscosity,fast response,and cyclic stability were prepared.These hydrogel sensors showed good application prospects in human activity and physiological health monitoring.This thesis will further promote the research progress of hydrogel materials in the fields of artificial intelligence,soft robots,electronic skin,etc.,and have important reference significance for the design of wearable smart materials in the future.