Research On Wearable Strain Sensor Based On Carbon Nanomaterial-polymer Hydrogel

The hydrogel strain sensor has aroused great interest in the field of artificial intelligence and human health monitoring due to its large stretchability and compressibility,high biocompatibility,self-healing and self-adhesive properties.Carbon nanomaterials（including carbon nanofibers and carbon nanotubes）have good electrical conductivity and excellent mechanical properties,and can be used as conductive fillers to combine with polymer hydrogels to prepare functional conductive hydrogels.CFP was prepared by chemical vapor deposition（CVD）,after treating with nitric acid solution for hydrophilic treatment,drying and further grounding for dispersing,the hydrophilic CFP was added to the dissolved PVA aqueous solution,and the CFP/PVA nanocomposite conductive hydrogel was obtained after 3 times freeze-thaw cycles.The hydrogel had a tensile strain of 366%,and would not break even under a compressive strain of 70%.Under tensile conditions,the hydrogel sensor exhibited a gauge factor（GF）of 0.183,and under compression,the GF was highly up to 6.321.Under 100%maximum tensile strain and 30%maximum compressive strain,after1000 loading-unloading cycles,the relative resistance change rate（ΔR/R₀）always respectively remained at 11.4%and-71%without significant fluctuations,showing good cycle stability.In addition,the hydrogel sensor could effectively monitor the finger bending,wrist bending,walking and other large-scale motion behaviors.Self-assembled multi-walled carbon nanotube sponge was dispersed by concentrated nitric acid to obtain hydrophilic MWCNTs,with the addition of2,2’-Azobis（2-methylpropionamidine）dihydrochloride（AIBI）initiator and N,N-Methylenebisacrylamide Bis-acrylamide（MBAA）cross-linking agent into the dispersion containing multi-walled carbon nanotubes（MWCNTs）,polyvinyl alcohol（PVA）and acrylamide（AAm）,the MWCNT/PVA/PAAm nanocomposite conductive hydrogel was obtained through in-situ polymerization at 60℃for 1 h.The hydrogel had a tensile strain of 535.5%and a tensile strength of up to 297.5 k Pa,and could withstand a compressive strain of 70%without damage.Under tensile conditions,the GF of the hydrogel sensor was highly up to 4.02.During 500 loading-unloading cycles（the maximum tensile strain is 100%）,theΔR/R₀ was maintained at 74%.Under compression conditions,the GF of the hydrogel sensor was 0.0068 k Pa^-1,and theΔR/R₀ was maintained at-26.44%during the 500 loading-unloading cycles（the maximum compressive strain is 30%）.At the same time,the hydrogen bonds in the hydrogel made the hydrogel sensor have a self-repairing efficiency of 40.56%after being destroyed.In addition,PVA carries a large number of hydroxyl groups,the hydrogel exhibited excellent adhesion to human skin and a variety of substrates（including quartz,plastic,copper,steel,NBR,and paper）.Thanks to its high sensitivity and adhesion,the hydrogel sensor could not only accurately monitor large-scale motion behaviors such as finger bending and wrist bending,but also effectively monitor the small motion behaviors such as smiling and swallowing.