Iono-Elastomer-Based Wearable Strain Sensor with Real-Time Thermomechanical Dual Response

Abstract

An ultrastretchable iono-elastomer with resistance sensitive to both elongation strain and temperature has been developed by hierarchical self-assembly of an end functionalized triblock copolymer in a protic ionic liquid (ethylammonium nitrate) followed by cross-linking. Small-angle X-ray scattering experiments in situ with uniaxial elongation reveal a nanoscale microstructural transition of the hierarchically self-assembled cross-linked micelles that is responsible for the material's remarkable mechanical and ionic conductivity responses. The results show that the intermicelle distance extends along the deformation direction while the micelles organize into a long-range ordered face-centered-cubic structure during the uniaxial elongation. Besides good cyclability and resistance to selected physical damage, the iono-elastomer simultaneously achieves an unprecedented combination of high stretchability (340%), highly linear resistance vs elongation strain ( R = 0.998), and large temperature gauge factor (Δ R/ R = 3.24%/°C@30 °C). Human subject testing demonstrates that the iono-elastomer-based wearable thermomechanical sensor is able to effectively and accurately register both body motion and skin temperature simultaneously.

Underwater Communication and Optical Camouflage Ionogels

“…With the increase of tensile strain, the gauge factor (GF) of the sensor increased from 1.66 to 4.67, which was higher than that of other ionogel strain sensors. [ 54,55 ] Due to the strong self‐adhesion and stretchable properties of ionogels, the sensor can dynamically accommodate to the changes of human skin during movement, which makes it possible to monitor human motion in real‐time. For demonstration, the sensor was attached to a prosthetic finger to detect the bending–releasing motions of the prosthetic fingers.…”

A Mechanically Robust and Versatile Liquid‐Free Ionic Conductive Elastomer

“…Soft machines have made the transition from conventional electronics to ionotronics, exemplified by the emergence of a variety of ionotronic devices, such as stretchable touchpads, [ 1 ] skin‐like sensors, [ 2–4 ] ionic cables, [ 5,6 ] nanogenerators, [ 7 ] soft diodes, [ 8 ] and flexible displays. [ 9 ] Unlike electronic‐based devices, which rely mostly on electrons to conduct electricity, ionotronic devices function predominantly by the motion of ions, just as what living organisms do.…”

Advances in Materials for Soft Stretchable Conductors and Their Behavior under Mechanical Deformation

“…To decouple the two signals, a proposed solution is to calibrate a stretchable thermistor by adding a temperature-insensitive strain sensor for purely strain detection or vice versa where a strain sensor is paired with a strain-insensitive temperature sensor. Xie et al apply this technique to their temperature iono-elastomer, namely crosslinked self-assembled triblock copolymer micelles in ionic liquids, in a demonstration of the response tracking during high-intensity anaerobic exercise in Figure 15 [ 242 ] where the iono-elastomer temperature sensing portion was immobilized from strain. Other stretchable ionic temperature sensors also exhibit high linearity, high transparency, self-healing ability (as demonstrated in Figure 16 ) and can maintain stable conductivity under large deformations [ 133 , 243 ].…”

“…( c ) Human subject undergoing high-intensity anaerobic exercise with real-time strain and temperature responses captured by the sensor depicted in ( a ). Reprinted with permission from [ 242 ]. Copyright American Chemical Society 2018.…”