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

Abstract

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.

Flexible biodegradable transparent heaters based on fractal-like leaf skeletons

“…The most common types of thermotherapy pads are based on a heating component and a far-infrared paste or gel 11 . The conventional thermotherapy pads have many drawbacks that limit their usage in wearable devices 11,14,15 . The first drawback is the lack of transparency, which is necessary to see the treatment effect without the need for removing the pads.…”

Thermally Controlled, Active Imperceptible Artificial Skin in Visible‐to‐Infrared Range

“…It is highly significant that the device does cloak the human body actively with high wearability and switchability between the visible and IR spectrum bands as a complete working wearable device because most of the previously reported devices so far only suggested the fundamental concepts that merely examine prospective potential. [10,15,24,25]…”

“…Inspired by the active and autonomous cloaking system from nature, recent technological advances offered a number of physical mechanisms to reconstruct the cloaking functionalities of cephalopods. Much of previous literature concentrated on altering colors within the visible wavelength using various methods such as electrochromic, thermochromic, and mechanochromic phenomena, [4][5][6][7][8][9][10][11] while several researches also delved into the cloaking techniques in the IR regime utilizing the metamaterials, [12][13][14] electro-actuation for IR reflection [15] or simply by adjusting device temperature to match background temperature [16] since the temperature (or radiated heat) can be directly translated into the IR signals. However, most of them realized either visible or IR imperceptible systems only; not dual modes in a single device structure that can readily switch between the visible and IR mode depending on a desirable situation.…”

Flexible electronics based on one‐dimensional and two‐dimensional hybrid nanomaterials

“…The flexible heaters that were fabricated exhibited fast and accurate response at various voltages. Kim et al reported stretchable film heaters using a spray‐coated AgNW/SWCNT hybrid composites that exhibit electrical and thermal stability without deterioration after 10 000 stretching cycles. The stretchable heater can be heated up to the target temperature (60°C) accurately even during a stretching state with the tensile strain of 50% (Figure H).…”