Studies on Wrinkled Elastomeric Polymer-Based Multifunctional Electronic Skin

Abstract

Various artificial electronic skins (E-skin) with multi-functionality, high sensitivity, and stretchability that mimic the sensory abilities and deformability of human skin have been reported. More recently, research on E-skin has developed additional fascinating features, such as self-healing and self-powered operation. Despite these advances, the imperfect stimulus discriminability, restrictive directional stretchability, and hardness in recognition of output signal have not been overcome, i.e. previously-reported E-skins provided inaccurate and distorted information to users when several stimuli with a range of dynamic intensities are mixed, as in daily life. In addition, most reported multi-functional E-skins exhibit only uni/bidirectional stretchability, so their high stretchability cannot be sustained over every direction of the tensile strain. Thirdly, to acquire the electric signal from e-skin, additional bulky instruments are applied for detection. In chapter 2, an omnidirectionally and highly stretchable electrode is demonstrated. The stretchability under various angle of tensile strain is obtained by introducing a hybrid of in- / out of-plane zigzag structure with silver nanowire arrays. To fabricate the stretchable electrode, wrinkled PDMS template for transferring silver nanowire is utilized. The as-prepared silver nanowire (AgNW) arrays on elastic substrate exhibit high stretchability up to 210% under a uniaxial strain and 125% under a biaxial one, without any severe degradation in its electrical conductance. Furthermore, the AgNW array film also shows “omnidirectionality”, which implied the high stretchability under randomly chosen stress direction. A stretchable sensor for electronic skin is also demonstrated to confirm the application of our approach to soft electronics. In chapter 3, user-interactive electronic skin (e-skin) with a human-recognizable output is fabricated, based on incorporating a thermochromic composite in a stretchable strain sensor comprising strain-responsive silver nanowire networks and physiochemical patterned silicone elastomer. Both its color and heat are easily controlled through electrical resistance variation induced by applied mechanical strain. The resulting monolithic device exhibits not only significant changes in optical reflectance and temperature but also additional functions such as a durable rapid response, high stretchability, and linear sensitivity. This approach allows a low-expertise route to fabricating dynamic interactive thermotherapeutic e-skins that can be applied to effectively rehabilitate injured connective tissues as well as prevent skin burns by simultaneously providing heat, stretch, and color change. In chapter 4, Human skin plays an important role to communicate with an environment by diverse types of activity such as touch, dragging, or deforming object. In this manner, many researcher have developed various kinds of electronic skin (e-skin) device which mimics a functional or geometrical ability of the human skin. However, advances in shear force detectable e-skin remain lack. This approach to achieving a stretchable multimodal device for shear force detection is based on hybrid electrical properties of piezoelectric, triboelectric, and piezoresistive. The as-prepared e-skin is composed of patterned silicon elastomer, hybrid nanomaterials of silver nanowire and zinc oxide nanowire / nanoparticle, and thin dielectric covered on the patterned. This versatile devise can recognize and distinguish the mechanical stress not only from single, pressure, tensile strain, and dynamic touch to multiple including combination of static pressure / dynamic touch, dynamic strain / dynamic touch, and static pressure / static strain. The shear force is characterized by sensing the multiple stimuli of pressure, tensile strain, and dynamic touch. This approach allows texture recognitions for biomimetic prosthesis by applying the multifunctional e-skin on robotic hands.