Preparation Of Polyvinyl Alcohol-based Conductive Hydrogel And Its Application In Flexible Strain Sensors

Polyvinyl alcohol(PVA)-based conductive hydrogels are widely used in flexible wearable sensors due to their excellent flexibility,elasticity and biocompatibility.However,the low conductivity and poor functionality of traditional PVA-based conductive hydrogels limit their applications.Therefore,how to improve the conductivity and functionality(such as freezing resistance,water retention)of PVA-based hydrogels has attracted great attention.In this thesis,PVA hydrogel substrate was first prepared by freeze-thaw cycle method.The water retention and freezing resistance of PVA hydrogel were improved by adding antifreeze agent into the substrate.Then two in-situ deposition methods were utilized to enhance the conductivity of PVA hydrogel.The water retention and freezing resistance,mechanical properties,electrical conductivity and strain-sensing application of the obtained samples were studied.(1)PVA/EG/PPy conductive hydrogels were prepared by introducing ethylene glycol(EG)as the antifreeze agent into PVA substrate and the subsequent in-situ deposition of polypyrrole(PPy).The influence of EG content on water retention was investigated,and composite hydrogels with good freezing resistance and water retention were obtained.The mechanical properties and electrical conductivity of the hydrogel were studied by adjusting the PVA concentration and Py content.The PVA/EG/PPy hydrogel with good fatigue resistance,tensile properties and high conductivity(2.48 S/m)was obtained,which was further attached to the human body to study its sensing performance and application.The as-prepared flexible strain sensor has fast strain response(125 ms),wide strain detection range(0%-150%)and high sensitivity(GF = 1.45).(2)In order to further improve the conductivity and the strain sensing performance of PVA/EG-based conductive hydrogels,PVA/EG/Ag conductive hydrogels were prepared by in-situ deposition of silver nanoparticles(Ag NPs)onto PVA/EG hydrogel.The effects of the concentration of silver trifluoroacetate solution and soaking time on the mechanical properties and electrical conductivity of the hydrogel were investigated.The obtained conductive hydrogel sensor has good mechanical properties,high conductivity(2778 S/m),high sensitivity(GF = 20.73)and low strain detection limit(0.1 %).The applications of PVA/EG/Ag conductive hydrogel in human joint activity,facial expression,throat vocalization and pulse monitoring were further explored.