Highly Stretchable and Wearable Thermotherapy Pad with Micropatterned Thermochromic Display Based on Ag Nanowire–Single‐Walled Carbon Nanotube Composite

• Published in: Advanced functional materials 2019-06, Vol.29 (24), p.n/a
• Main Authors: Kim, Hyunmin, Seo, Minjeong, Kim, Jong‐Woo, Kwon, Do‐Kyun, Choi, Song‐Ee, Kim, Jin Woong, Myoung, Jae‐Min
• Format: Article
• Language: English
• Subjects: Ag NW–SWCNT composite; Electrical resistivity; Materials science; Medical electronics; Microfluidics; Microparticles; micropatterned thermochromic display; Micropatterning; Nanowires; Polydimethylsiloxane; Rubbing; Silicone resins; Silver; Single wall carbon nanotubes; Stretchability; stretchable film heater; Substrates; Tensile strain; thermotherapy pad; wearable devices; Wearable technology
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201901061

Due to the increasing interest in wearable devices, flexible and stretchable film heaters have been widely studied, as alternatives to heaters with conventional rigid shapes. Herein, a highly stretchable film heater (SFH) based on the silver nanowire (Ag NW)–single‐walled carbon nanotube composite with a thermochromic display on a polydimethylsiloxane (PDMS) substrate is successfully fabricated. The SFH shows excellent electrical conductivity, high mechanical stretchability, and outstanding reliability, with no significant degradation after 10 000 stretching cycles under tensile strain. The SFH can be heated to the target temperature (≈60 °C) within 30 s at a low applied voltage. In addition, a thermochromic display is fabricated to help prevent the risk of low‐temperature burns. Red (R), green (G), and blue (B) thermochromic microparticles (TMPs) are synthesized using drop‐based microfluidic technology. The TMPs show RGB colors at room temperature but change to a white color above a certain temperature. The TMPs are arrayed into a PDMS stencil on the basis of their particle sizes using the rubbing technique. The micropatterned thermochromic display, which functions as a visual alarm, combined with the SFH can pave the way for the development of thermotherapy pads for next‐generation wearable devices in the medical field. A highly stretchable and wearable thermotherapy pad with a micropatterned thermochromic display based on a Ag nanowire–single‐walled carbon nanotube composite is demonstrated. It has a low resistance, high stretchability, and excellent reliability. Moreover, the thermochromic display has a built‐in visual alarm mechanism to prevent low‐temperature burns. This promising articular thermotherapy pad has potential applications in the medical field.