关键词: 水凝胶, 复合电极, 炭黑, 应变传感性能, 人体运动监测

Abstract: "Hydrogels, as soft materials featuring three-dimensional crosslinked networks with high water content, have been extensively utilized in wearable strain sensing applications. To expand the application of hydrogels in flexible strain sensors, composite conductive hydrogels are prepared by in-situ polymerization to have high adhesive properties, mechanical stability, and high response sensitivity. First, carbon black (CB) was added to DA/NaOH aqueous solution, and DA was oxidized and polymerized in situ on the surface of CB to form PDA-decorated CB (PDA-CB). Second, acrylamide (AM) monomers, acrylic acid (AA) monomers, ammonium persulfate (APS), and N,N'-methylenebisacrylamide (BIS) were added to the PDA-CB dispersion as chemical initiators and crosslinkers, to form the gel precursor suspension. Finally, glycerol was added to form a glycerol-water binary solvent system within the gel. After degassing the gel precursor suspension under vacuum at room temperature for 2 hours, the resulting suspension was used to produce a composite conductive hydrogel (CHS). The microscopic characterization of CHS precursor suspension revealed that carbon black particles were uniformly dispersed within the hydrogel matrix, exhibiting a chain-like and network distribution, conducive to enhancing the electrical properties. With the increase of carbon black dosage, the stress experienced by the CB hydrogel at the same elongation increased, confirming the enhancement of mechanical strength through CB incorporation. However, when the carbon black content in the suspension exceeded a certain threshold, the mechanical and electrical properties of the hydrogel declined. This was attributed to the fact that an excessive amount of carbon black particles tended to agglomerate, leading to stress concentration and subsequent fracture in the hydrogel. Furthermore, the agglomeration of carbon black within the hydrogel matrix hinderd electron transport in the gel system, thereby reducing the conductivity of the hydrogel. In addition, dopamine hydrochloride (DA) was introduced and could be coated on the surface of carbon black particles in an alkaline environment and polymerized in situ to form polydopamine (PDA), enhancing the recombination of carbon black particles and hydrogel matrix, and promoting the uniform dispersion of carbon black particles within the hydrogel matrix. The resulting CHS hydrogel exhibits high tensile elongation at break and adhesion/tear strength. The properties of the CHS hydrogel, prepared by incorporating DA into the CB hydrogel, demonstrate a significant enhancement. The composite conductive hydrogel CHS exhibits good adhesion to various substrates, and the strain coefficient can reach up to 2.191 during the tensile process, showing excellent response sensitivity. It demonstrates good response stability under different deformation levels and frequencies, and good stability after cyclic stretching for 1,500 cycles under 50% deformation."

Key words: hydrogels, composite electrode, carbon black, strain sensing performance, human motion monitoring