Visco‐Poroelastic Electrochemiluminescence Skin with Piezo‐Ionic Effect

Abstract

Following early research efforts devoted to achieving excellent sensitivity of electronic skins, recent design schemes for these devices have focused on strategies for transduction of spatially resolved sensing data into straightforward user‐adaptive visual signals. Here, a material platform capable of transducing mechanical stimuli into visual readout is presented. The material layer comprises a mixture of an ionic transition metal complex luminophore and an ionic liquid (capable of producing electrochemiluminescence (ECL)) within a thermoplastic polyurethane matrix. The proposed material platform shows visco‐poroelastic response to mechanical stress, which induces a change in the distribution of the ionic luminophore in the film, which is referred to as the piezo‐ionic effect. This piezo‐ionic effect is exploited to develop a simple device containing the composite layer sandwiched between two electrodes, which is termed “ECL skin”. Emission from the ECL skin is examined, which increases with the applied normal/tensile stress. Additionally, locally applied stress to the ECL skin is spatially resolved and visualized without the use of spatially distributed arrays of pressure sensors. The simple fabrication and unique operation of the demonstrated ECL skin are expected to provide new insights into the design of materials for human–machine interactive electronic skins.

Flexible Biosensors Based on Colorimetry, Fluorescence, and Electrochemistry for Point-of-Care Testing

“…Electronic skin is a network of electronic sensors with mechanical deformation capabilities that are able to sense a variety of external stimuli like chemical, mechanical and thermal stimuli (Heikenfeld et al, 2018;Xu et al, 2019;Yang and Gao, 2019). Lee's group presented an electronic skin capable of converting mechanical stimuli into visual readouts (Lee et al, 2021). The material layer of the electronic skin is made of a physically cross-linked polymer matrix with a mixture of ionic transition metal complexes (ITMC) and ionic liquids (IL) encapsulated in it.…”

Porous Ion Gel: A Versatile Ionotronic Sensory Platform for High-Performance, Wearable Ionoskins with Electrical and Optical Dual Output

“…This feature is advantageous over the previous simple on/off touch system 45 and flat film-based optical sensor limited to ∼60 kPa. 46 The pressure-dependent optical readout could be observed even by the naked eye (see inset in Figure 5e), indicating a high potential for functional pressure sensory systems that directly display the magnitude of the applied pressure via luminance. As a proof-of-concept demonstration, we attached the ECL ionoskin to finger (Figure 5f).…”

Emerging Iontronic Sensing: Materials, Mechanisms, and Applications

“…The piezoelectric effect under deformation is originated from (i) the instantaneous stress distribution along the direction normal to the applied force established in the piezoelectric polymers and (ii) the different migration capabilities of the ionic constituents upon the built-in stress distribution in the polymer. The components with strong mobility will escape away from the interface where the force is applied, whereas components with weak mobility prefer to remain at the interface [ 127 ].…”

“…Through attaching sensor arrays on hand joints, different sign languages can be distinguished via analysis of the detected output electrical signals. Lee et al devised a piezoluminescent iontronic device that exhibited a visco-poroelastic response to mechanical pressure due to the change of inside-ion distribution [ 127 ]. When the sensor is subjected to pressure, positive and negative charge spaces will be built, which is indicated by the open-circuit voltage values upon varied pressures.…”