Fabrication of a Highly Stretchable, Wrinkle‐Free Electrode with Switchable Transparency Using a Free‐Standing Silver Nanofiber Network and Shape Memory Polymer Substrate

Abstract

Transparent and stretchable electrodes (TSEs) are a key technology for the next generation of stretchable electronics and optoelectronics. Metallic nanofibers are widely used because of their good optoelectrical properties, but they demonstrate low stretchability. To enhance stretchability, fabricating in‐plane buckled nanofibers with the aid of a prestrained substrate has become crucial in this research field. Here, a composite comprising shape memory polymer–TSE (SMP–TSE) using crosslinked polycyclooctene as a substrate, which shows wrinkle‐free deformation and switchable optical transparency, is fabricated. Because of its considerable elongation without residual strain and the shape memory behavior of polycyclooctene, in‐plane buckled nanofibers are formed effectively. For fabrication of SMP–TSE, continuous and thin metallic nanofiber that can maintain its structural integrity is required; therefore, electrospinning and an ultraviolet reduction process to create a free‐standing, conductive, nanofiber network are used. Because of its in‐plane buckled nanofibers, the electrode maintained its resistance during 3000 cycles of a bending test and 900 cycles of a tensile test. Furthermore, SMP–TSE is able to electrically control its temperature, optical transparency, elastic modulus, and shape memory behavior. Finally, the use of SMP–TSE in a smart display that can control its optical and mechanical properties is demonstrated.

Shape-Memory Materials via Electrospinning: A Review

“…Yoon et al [225] fabricated an SMP-TSE (transparent and stretchable electrode) composite constituted by a continuous silver nanofiber (AgNF) network with optical and electrical properties, where electrical conductivity can be increased with flexibility, and crosslinked polycyclooctene (PCO) as a stretchable substrate with shape-memory behavior, showing R f values above 96% and R r values above 97%, which revealed switchable optical transparency and potential applications as skin-like electronic devices.…”

Electrothermally Actuated Semitransparent Shape Memory Polymer Composite with Application as a Wearable Touch Sensor

“…In targeting wearable electronics, semitransparent conductors are a useful building block that can be integrated into a variety of devices and applications, such as artificial skins, , photovoltaics, and touch screens. , While a majority of SMP materials used in electronics are opaque or hazy, − visibly semitransparent SMP conductive composites have been demonstrated. − One such example is a transmittance tunable SMP:Ag nanofiber electrode based on the crosslinked SMP polycyclooctene and electrospun Ag nanofibers (with greater length and diameter compared with NWs). The SMP microstructure changes when crossing a transition temperature, increasing its transmittance as a result of melting of the crystalline phase . Another semitransparent SMP composite consisted of a commercial UV-resin (NOA 68) with embedded silver nanowires (AgNWs) to realize flexible semitransparent electrodes for organic photovoltaic devices .…”

Soft and Stretchable Liquid Metal Composites with Shape Memory and Healable Conductivity

“…In general, shape memory materials are promising due to their ability to store and relax back their elastic energy when triggered by several external stimuli such as heat, light, electricity, and magnetic fields. − The ability to change shape is useful for designing structures to fulfill various demands such as functionality, durability, and shape conformability. − Among various materials, soft and stretchable shape memory composites with electrical conductivity are potentially useful for unconventional electronics such as stretchable displays, , soft robotics, − and wearable sensors. − …”

“…1−7 The ability to change shape is useful for designing structures to fulfill various demands such as functionality, durability, and shape conformability. 8−16 Among various materials, soft and stretchable shape memory composites with electrical conductivity are potentially useful for unconventional electronics such as stretchable displays, 17,18 soft robotics, 19−22 and wearable sensors. 23−30 Several methods have been developed for fabricating soft and stretchable shape memory composites with electrical conductivity.…”