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

摘要： 为了提高复合导电水凝胶电极的力学稳定性、响应灵敏度及与人体皮肤的粘合牢度，将盐酸多巴胺（DA）原位聚合在炭黑颗粒（CB）表面，使炭黑与聚丙烯酸/丙烯酰胺（PAA/PAM）水凝胶基底具有良好相容性，从而制备出炭黑/水凝胶复合电极（CHS）。采用透射电子显微镜、电化学工作站、高铁检测仪等分析CB浓度及DA浓度对导电水凝胶的电学、力学及粘附性能的影响。结果表明：CB在水凝胶基底中形成连续的导电网络，当CB与DA的用量均为4 mg/mL时，CHS的断裂伸长率达到175%，电导率为0.056 S/m，响应灵敏度为2.191，在30%~90%的应变范围内表现出线性响应；在50%形变下，循环拉伸1500次后仍能保持良好的响应稳定性。此外，CHS水凝胶复合电极展现出良好的黏附性，能够直接黏附于人体皮肤，并实时监测手指、手腕弯曲及咽喉吞咽动作。

关键词: 水凝胶, 复合电极, 炭黑, 应变传感性能, 人体运动监测