Silver Nanoparticle-Decorated Multiwalled Carbon Nanotube Ink for Advanced Wearable Devices

Silver nanoparticles of average size 12-13 nm were successfully decorated on the surface of multiwalled carbon nanotubes (MWCNTs) through a scalable wet chemical method without altering the structure of the MWCNTs. Employing this Ag@MWCNT, a multifunctional room-temperature curable conductive ink was developed, with PEDOT:PSS as the conductive binder. Screen printing of the ink could yield conductive planar traces with a 9.5 μm thickness and a conductivity of 28.99 S/cm, minimal surface roughness, and good adhesion on Mylar and Kapton. The versatility of the ink for developing functional elements for printed electronics was demonstrated by fabricating prototypes of a wearable strain sensor, a smart glove, a wearable heater, and a wearable breath sensor. The printed strain sensor exhibited a massive sensing range for wearable applications, including an impressive 1332% normalized resistance change under a maximum stretchability of 23% with superior cyclic stability up to 10 000 cycles. The sensor also exhibited an impeccable gauge factor of 142 for a 5% strain (59 for 23%). Furthermore, the sensor was integrated into a smart glove that could flawlessly replicate a human finger's gestures with a minimal response time of 225-370 ms. Piezoresistive vibration sensors were also fabricated by printing the ink on Mylar, which was employed to fabricate a smart mask and a smart wearable patch to monitor variations in human respiratory and pulmonary cycles. Finally, an energy-efficient flexible heater was fabricated using the developed ink. The heater could generate a uniform temperature distribution of 130 °C at the expense of only 393 mW/cm² and require a minimum response time of 20 s. Thus, the unique formulation of Ag@MWCNT ink proved suitable for versatile devices for future wearable applications.