Interfaceless Strain and Pressure‐Sensitive Stretchable Capacitor Based on Self‐Bonding and Surface Morphology Control of a Reversibly Crosslinkable Silicone Elastomer

Abstract

the changes in electrical parameters (such as conductivity and impedance) or the geometry of a specific material produced by small mechanical deformations. [22] Here, general requirements for an excellent mechanical sensor usually refer to a high gauge factor (the ratio of the relative changes in the measured property to the mechanical strain), but in the case of a stretchable strain and pressure sensor, some other conditions must also be satisfied. The implementation of stretchable sensors means that the sensor must be elastic enough to be stretched or shrunk beyond a certain level, the performance of the sensor should not be degraded even when it is stretched, and the sensor should be able to withstand repeated stretch-and-release.Capacitive sensors, which transduce a physical contact with a conductive object (such as human finger) into a change in capacitance, have been used in commercial touch sensors as they have a short response time, a simple read-out mechanism, and high sensitivity even under extremely weak interactions with an external conductive object. [23] The capacitive sensory mechanism has also been employed to obtain pressure sensors by using a layer of soft dielectric polymer sandwiched between two flexible transparent electrode layers, where the capacitance is formed. [22,24] When pressure is applied to the sensor, the thickness of the inserted dielectric layer between the two electrodes is reduced, resulting in an increase in capacitance, which can be used as a sensing parameter. In order for the pressure sensor to have stretchability, all elements constituting the sensor, that is, the upper and lower substrate, the centering dielectric layer, and the electrodes, should have large elasticity or sufficient conductivity even in the stretched state. Furthermore, the interface between each layer in the pressure sensor should be chemically robust so that delamination or severe plastic deformation at the interface can be prevented after repeated stretch-and-release.In this respect, the most ideal sensor structure is that all components except the electrodes are formed of the same material, or at least share equivalent physical/mechanical properties. Unfortunately, most stretchable pressure sensors reported so far have been fabricated by bonding two elastic polymer substrates with an adhesive [25][26][27] or by coating a liquid oligomer on a pre-cured polymer film to form a multilayer [28] ; thus, it is A typical capacitive mechanical sensor implemented using a layer of soft dielectric polymer sandwiched between two flexible electrodes, where the capacitance is formed, suffers from unintended buckling instability upon repeated stretch-and-release owing to different mechanical characteristics of constituent materials and unstable interfaces. Here, a stretchable, healable, and transparent strain/pressure-sensitive capacitor is successfully fabricated by hybridizing Ag nanowires (AgNWs) with a polydimethylsiloxane containing maleimide-derived Diels-Alder (DA) adducts as reversible crosslinkers. AgNWs for...

Convolution Neural Networks for Motion Detection with Electrospun Reversibly-Cross-linkable Polymers and Encapsulated Ag Nanowires

“…Changes in the material properties could also arise from contact with external materials. Third, since electrodes are formed on a single surface of the polymer, a considerable disparity in mechanical properties between the conductors such as Ag nanowires (AgNWs) and the elastomer leads to asymmetry in film properties. , This induces a complex stress environment in the presence of curvature-forming stress, obfuscating the origin of resistance changes. Thus, the optimal resistive motion sensor structure would entail the formation of electrodes between two identical films with the contact area between the films chemically integrated.…”