Recently, a paper-based (PB) strain sensor has turned out to be an ideal substitute for the polymer-based one because of the merits of renewability, biodegradability, and low cost. However, the hygroexpansion and degradation of the paper after absorbing water are the great challenges for the practical applications of the PB strain sensor. Herein, the superhydrophobic electrically conductive paper was fabricated by simply dip-coating the printing paper into the carbon black (CB)/carbon nanotube (CNT)/methyl cellulose suspension and hydrophobic fumed silica (Hf-SiO2) suspension successively to settle the problem. Because of the existence of ultrasensitive microcrack structures in the electrically conductive CB/CNT layer, the sensor was capable of detecting an ultralow strain as low as 0.1%. During the tension strain range of 0-0.7%, the sensor exhibited a gauge factor of 7.5, almost 3 times higher than that of the conventional metallic-based sensors. In addition, the sensor displayed frequency-independent and excellent durability and reproductivity over 1000 tension cycles. Meanwhile, the superhydrophobic Hf-SiO2 layer with a micro-nano structure and low surface energy endowed the sensor with outstanding waterproof and self-cleaning properties, as well as great sustainability toward cyclic strain and harsh corrosive environment. Finally, the PB strain sensor could effectively monitor human bodily motions such as finger/elbow joint/throat movement and pulse in real time, especially for the wet or rainy conditions. All these pave way for the fabrication of a high-performance PB strain sensor.
Keywords: human bodily motion; paper; strain sensor; superhydrophobic; ultrasensitive.