Preparation And Properties Of Flexible Sensors Based On Multifunctional Conductive Hydrogels

In recent years,wearable flexible sensors have attracted great interest with the development of electronic skin,human movement monitoring,clinical diagnosis and human-computer interaction.Conductive hydrogels sensors have become a hotspot in the field of flexible sensors because of their excellent flexibility,biocompatibility,tissue similarity and good sensing performance.However,conductive hydrogels sensors often face many problems including low strength,poor stability,poor adhesion,short service life and complex preparation process,which greatly limit their further application.Focusing on the above-mentioned problem,we designed a series of hydrogels with high strength,self-healing,anti-freezing,moisture retention and adhesion.The structure and properties of conductive hydrogels were investigated,and the human movement and physiological activities were examined in detail.The main work is summarized as follows:1.ANF-PVA/PANI hydrogels flexible sensors with high strengthTo provide flexible sensor hydrogels with excellent mechanical strength and high sensitivity simultaneously,the aramid nanofiber-polyvinyl alcohol（ANF-PVA）hydrogels were prepared by solvent exchange method.Conductive ANF-PVA/polyaniline（PANI）hydrogels were synthesized by in-situ polymerization of aniline with ANF-PVA hydrogels as template.The structure and properties of ANF-PVA/PANI hydrogels have been systematically studied.The stable ANF-PVA/PANI network is constructed by the hydrogen bond andπ-πconjugation between conductive PANI and ANF-PVA.The optimized ANF-PVA/PANI hydrogels sensors have excellent tensile strength（2.4 MPa）,elongation at break（140%）and high sensitivity（GF=39）.The hydrogels sensors can stably and repeatedly（1000 times）measure the strain change.It can accurately monitor human movements such as joints,pulse,mouth bulging,swallowing and speaking.The research results provide a new method for the design of flexible wearable sensors with high mechanical properties and sensitivity.2.OSA/PACA/Fe³⁺hydrogels flexible sensors with self-healing propertyIt is great challenge to construct hydrogels with excellent mechanical properties and good self-healing properties.In this paper,the sodium alginate oxide（OSA）/poly（acrylamide-co-acrylic acid）（PACA）/Fe Cl₃(OSA/PACA/Fe³⁺)ionic conductive hydrogels were synthesized by a simple one-pot method.Multiple dynamic bonds including hydrogen bonds（between OSA and PACA）,coordination interactions(among PACA、OSA and Fe³⁺),and imine bonds（between OSA and PACA）were constructed in OSA/PACA/Fe³⁺ionic conductive hydrogels.The relationship between structure and properties of OSA/PACA/Fe³⁺hydrogels was studied in detail.The optimized OSA/PACA/Fe³⁺hydrogels have excellent mechanical properties（elongation at break of 830%and tensile strength of 0.37 MPa,respectively）.After 12h healing time,the self-healing efficiency of OSA/PACA/Fe³⁺hydrogels can reach 90%.In addition,sensors based on OSA/PACA/Fe³⁺hydrogels show controllable conductivity（0.0145～0.0993 S/m）and high tensile sensitivity（GF=7.8）,which can accurately and stably detect human movements and physiological stimulus.The results provide a new way to design hydrogels with excellent self-healing properties and mechanical properties.3.OSA/PAm/PMXene/Gly hydrogels flexible sensors with anti-freezing and moisture retentionIt is important for hydrogels to maintain stable mechanical properties,adhesion ability and sensitivity at extreme condition（high or low temperatures）.In this paper,Ti₃C₂T_X（MXene）was modified by polydopamine（PDA）.Then acrylamide（Am）was polymmerizaed in the presence of PDA-MXene（PMXene）,sodium alginate oxide（OSA）,glycerin（Gly）and water.The OSA/PAm/PMXene/Gly conductive hydrogels were prepared by a simple one-pot method.The stability of mechanical properties and sensing properties of hydrogels at high and low temperatures（-20～60℃）were enhanced due to the strong hydrogen bonds interaction between Gly and water.The designed OSA/PAm/PMXene/Gly hydrogels sensors have excellent mechanical properties（elongation at break of 1037%,tensile strength of 0.17 MPa）,high sensitivity（GF=2.2）and adhesion behavior（adhesion strength with pig skin of 17.3 k Pa）.The OSA/PAm/PMXene/Gly sensors have high sensing stability in high and low temperature（from-20 to 60℃）,and they can stably detect different human motions in a wide temperature range.The research results provide a new solution for the use of flexible wearable sensors in extreme ambient temperatures.4.Rapid polymerization of BCW-TA/PAA/Fe³⁺/Gly hydrogels flexible sensors with multifunctionalityIn order to synthesize conductive hydrogels with multifunctional properties through a facile and fast method,bacterial cellulose nanowhisker-tannic acid/polyacrylic acid/Fe³⁺/glycerol(BCW-TA/PAA/Fe³⁺/Gly)hydrogels with high strength,self-healing and adhesion were rapidly polymerized by activation of amine persulfate（APS）at room temperature based on the catalytic system of TA-Fe³⁺and Gly.The unique conductive hydrogels network was constructed by hydrogen bonds and metal coordination among BCW-TA,PAA and Fe³⁺.The relationship between structure and properties of BCW-TA/PAA/Fe³⁺/Gly hydrogels was investigated systematically.The combination of TA and Fe³⁺can initiate the polymerization of AA quickly,because the redox pairs formed by TA and Fe³⁺can activate APS at room temperature to produce a large number of sulfate radicals,which leads to the rapid free radical polymerization of acrylic acid（AA）monomer.In addition,Gly can promote the automatic acceleration of AA,and further improve the polymerization rate of AA.The optimized BCW-TA/PAA/Fe³⁺/Gly hydrogels sensors have high mechanical properties（elongation at break is 1950%,tensile strength is 0.203 MPa）,excellent self-healing property（the self-healing efficiency can reach 91%after 6 h）,good sensitivity（GF can reach 5.2 in1200～1900%strain range）and wide working temperature range（-20～60℃）.The hydrogels sensors with good antibacterial property and biocompatibility,and can be directly adhered to the skin to monitor different ranges of muscle movements and physiological activities.The results provide a technical basis for the rapid preparation of multifunctional flexible hydrogels sensors.