Stretchable, Transparent, Ionic Conductors

Abstract

Existing stretchable, transparent conductors are mostly electronic conductors. They limit the performance of interconnects, sensors, and actuators as components of stretchable electronics and soft machines. We describe a class of devices enabled by ionic conductors that are highly stretchable, fully transparent to light of all colors, and capable of operation at frequencies beyond 10 kilohertz and voltages above 10 kilovolts. We demonstrate a transparent actuator that can generate large strains and a transparent loudspeaker that produces sound over the entire audible range. The electromechanical transduction is achieved without electrochemical reaction. The ionic conductors have higher resistivity than many electronic conductors; however, when large stretchability and high transmittance are required, the ionic conductors have lower sheet resistance than all existing electronic conductors.

Ionic skin

“…These ionic interconnects mimic the function of axons, and can be as long as meters, if required by an application. [18] Both the dielectric and the ionic conductors are stretchable and transparent, whereas the electronic conductors can be made of stiff and opaque metals. This design allows a large-area sheet of distributed sensors to be highly stretchable and transparent.…”

“…[18][19][20] These gels are polymeric networks swollen with water or ionic liquids. They behave like elastic solids and eliminate the need for containers as required in the case of liquid metal conductors.…”

“…Although most hydrogels dry out in open air, hydrogels containing humectants retain water in environment of low humidity, and ionogels are nonvolatile in vacuum. [18][19][20] We have recently used ionic conductors-together with stretchable and transparent dielectrics-to make actuators, which deform in response to high voltages, on the order of kilovolts. [18] By contrast, the sensors described here deform in response to applied forces, giving signals that can be measured using voltages below 1 volt.…”

Toward Perceptive Soft Robots: Progress and Challenges

“…Unfortunately, most good conductors (metals and metal alloys) have a very poor stretchability (only 3–5%). Currently, there are two approaches to develop stretchable conductors ( Figure 7 ): material approach (e.g., nanocomposite,110 liquid conductor,111 conductive polymer/hydrogel,57, 112 etc.) and structural approach (e.g., bulking/wrinkling structure,113 kirigami patterning,114 textile,86 etc.).…”

“…c) Transparent loudspeaker using conductive ionic hydrogel. Reproduced with permission 112. Copyright 2013, AAAS.…”