Transparent and conformal 'piezoionic' touch sensor

Abstract

A polyurethane hydrogel based touch sensor with high transparency and conformability is demonstrated. Polyurethane hydrogels swollen with various electrolytes were compressed at a pressure of 30 kPa, simulating a fingertap on a conventional touch screen device. Unlike ionic polymer metal composite and conducting polymer trilayer sensors, where electrodes render the sensors opaque and relatively rigid, the electrodes used in this work are metal wires or strips, separated from each other by regions of transparent film, enabling transparency and compliance. The voltages and currents observed when the perturbation is above one electrode are on the order of 10(-2) V and 10(-7) A, relative to a second electrode that is approximately 1 cm away. The sign of voltage and current signals detected from perturbations made between electrodes is determined by relative proximity to each electrode, and the magnitude appears to decrease with increasing distance from the electrodes. These observations suggest that it may be possible to discriminate the location of touch based on signals transmitted to the edges of an ionically conductive film. A model to describe the inhomogeneous ionic distribution and predict the resultant voltage and current is presented to qualitatively explain the sensing, based on the Donnan potential. ABSTRACTA polyurethane hydrogel based touch sensor with high transparency and conformability is demonstrated. Polyurethane hydrogels swollen with various electrolytes were compressed at a pressure of 30 kPa, simulating a fingertap on a conventional touch screen device. Unlike ionic polymer metal composite and conducting polymer trilayer sensors, where electrodes render the sensors opaque and relatively rigid, the electrodes used in this work are metal wires or strips, separated from each other by regions of transparent film, enabling transparency and compliance. The voltages and currents observed when the perturbation is above one electrode are on the order of 10 -2 V and 10 -7 A, relative to a second electrode that is approximately 1 cm away. The sign of voltage and current signals detected from perturbations made between electrodes is determined by relative proximity to each electrode, and the magnitude appears to decrease with increasing distance from the electrodes. These observations suggest that it may be possible to discriminate the location of touch based on signals transmitted to the edges of an ionically conductive film. A model to describe the inhomogeneous ionic distribution and predict the resultant voltage and current is presented to qualitatively explain the sensing, based on the Donnan potential.

Poly(3,4‐ethylenedioxythiophene):Poly(styrene sulfonate)/Polyethylene Oxide Electrodes with Improved Electrical and Electrochemical Properties for Soft Microactuators and Microsensors

“…Shoa et al proposed a model, indicating that external application of stress alters the internal stress of ions, helping to insert or remove charge and as a consequence, to change the voltage . More recently, the “piezoionic effect” has been introduced to explain the voltage generation through inhomogeneous ionic distribution, based on the Donnan potential . All these ECP sensors were only described at macroscale, with variation of open circuit voltages (OCV) usually in the range of mV or lower.…”

“…Indeed, in the reported cases, an electrical signal relaxation is observed when maintaining constant strain, ultimately going back to initial value . This typical relaxation phenomenon can be explained by the piezoionic effect introduced by Sarwar et al When applying mechanical stimulation, the mechanically induced cation flux from the compressed electrode is creating disequilibrium of ions and generating the OCV variation. However, since both, cations and anions are mobile in classical electrolytes or ionic liquids, the less mobile anions are also diffusing over time, to progressively compensate this concentration difference.…”

PEDOT:PSS-based micromuscles and microsensors fully integrated in flexible chips

“…Based on the piezoionic mechanism, involving stress induced motion of the ions and their relative mobility, the expulsion of the more mobile EMI + cations from the mechanically compressed working electrode leads to the generation of negative open circuit potential. [25,35,36] Figure 3(c) demonstrates the increase in OCV response as a function of applied strain (step displacement of 200, 400 and 600 µm, corresponding to -0.11, -0.22 and -0.31 % strain difference). The maximum value of -0.17 mV is measured with an applied strain of -0.31 %.…”

Flexible Piezoionic Strain Sensors toward Artificial Intelligence Applications

“…As shown in Figure 2a , Madden et al have put forward piezoionic effect based on polyurethane hydrogel sensor. 10 The nonuniform deformation caused by mechanical perturbation can induce ion redistribution in polymer electrolyte, which will produce chemical potential change to compensate pressure from external deformation. And the chemical potential can be detected through connecting electrodes onto the hydrogel.…”