Electrothermally Actuated Semitransparent Shape Memory Polymer Composite with Application as a Wearable Touch Sensor

A semitransparent shape memory polymer (SMP):silver nanowire (AgNW) composite is demonstrated to be capable of low-temperature actuation, thus making it attractive for wearable electronics applications that require intimate contact with the human body. We demonstrate that the SMP:AgNW composite has tunable electrical and optical transparency through variation of the AgNW loading and that the AgNW loading did not significantly change the mechanical behavior of the SMP. The SMP composite is also capable of electrical actuation through Joule heating, where applying a 4 V bias across the AgNWs resulted in full shape recovery. The SMP was found to have high strain sensitivity at both small (<1%) and large (over 10%) applied strain. The SMP could sense strains as low as 0.6% with a gauge factor of 8.2. The SMP composite was then utilized as a touch sensor, able to sense and differentiate tapping and pressing. Finally, the composite was applied as a wearable ring that was thermally actuated to conformably fit onto a finger as a touch sensor. The ring sensor was able to sense finger tapping, pressing, and bending with high signal-to-noise ratios. These results demonstrate that SMP:AgNW composites are a promising design approach for application in wearable electronics.