Preparation And Properties Of Polypyrrole-based Conductive Hydrogels And Its Applications In Sensors

Conductive hydrogel which formed by the combination of hydrophilic matrix and conductive medium is a kind of soft material with good flexibility,water absorption and electrochemical performance.Conductive hydrogel has been widely concerned by researchers in electronic skin,supercapacitors,biomedical,flexible wearable electronic devices and other aspects.Among the common conductive polymers,polypyrrole is widely used in the preparation of conductive composites due to its excellent electrochemical performance,good stability and compatibility,and easy preparation.However,polypyrrole is rigid and hydrophobic,so it is difficult to disperse evenly in conductive hydrogel matrix,which reduces the comprehensive performance of conductive hydrogel and is difficult to meet the needs of many aspects.Therefore,how to make conductive polymers evenly distributed in the hydrogel network and build a good conductive pathway in the hydrogel network is still a major challenge.In this paper,polypyrrole(PPy)nanoparticle dispersion liquid was prepared with low molecular weight polypaspartic acid(LPASP)as dispersant.By mixing the PPy nanoparticle dispersion liquid with acrylic acid(AA)and acrylamide(AM)monomer,a conductive hydrogel with good comprehensive performance was prepared by free radical polymerization in aqueous solution.The conductive hydrogel was modified by adding β-cyclodextrin(β-CD)to compensate for the mechanical strength reduction caused by adding acrylic acid.The chemical structure,thermal stability and surface structure of the conductive hydrogel were characterized by infrared spectroscopy(FT-IR),TG-DSC synchronous analyzer and scanning electron microscope(SEM).The effects of different variables and component contents on the conductivity,swelling and mechanical properties of conductive hydrogels were investigated.The specific research contents are as follows:1.The dispersed and stable PPy nanoparticle dispersion liquid was prepared by using LPASP as dispersant and ammonium persulfate(APS)as initiator.Adding a certain amount of AM,N,N-methylene bisacrylamide(MBA)and initiator APS into PPy nanoparticle dispersion liquid,the LPASP/PAAm/PPy conductive hydrogel was prepared by radical polymerization.The chemical structure,thermal stability and surface structure of the conductive hydrogel were characterized by FT-IR,TG-DSC synchronous analyzer and SEM.The effects of different components and contents on the conductivity,water absorption and mechanical properties of hydrogels were investigated.The results showed that LPASP/PAAm/PPy conductive hydrogels not only had good electrochemical properties,but also had outstanding tensile properties.The conductivity up to 0.13 S/m and elongation at break of conductive hydrogels up to 1029%.The maximum tensile stress is 0.12 MPa.LPASP/PAAm/PPy conductive hydrogel is assembled into flexible strain sensor.When human body moves,obvious changes of electrical signals can be detected at different joints of human body,indicating that the sensor has good sensing ability.2.Under the addition of PPy nanoparticle dispersion solution,the LPASP/P(AA-AM)/β-CD/PPy composite conductive hydrogel was prepared by doping β-cyclodextrin(β-CD)with LPASP as dispersant,AA and AM as copolymers.LPASP can not only disperse PPy evenly in the hydrogel network,but also improve the biodegradability and biocompatibility of the conductive hydrogel.When LPASP and Py contents were 20 wt% and 2 wt%,respectively,the LPASP/P(AA-AM)/β-CD/PPy composite conductive hydrogel had high conductivity(1.11 S/m)and elongation at break was 1260%.At the same time,conductive hydrogel has good transparency.The flexible strain sensor assembled by LPASP/P(AA-AM)/β-CD/PPy composite conductive hydrogel can not only monitor the human body’s large movements such as elbow bending,wrist bending,finger bending and fist clenching,but also detect the slight vibration caused by swallowing while drinking water.