Formation of Functional Nanofibers and Their Applications for Wearable Electronics

Abstract

The electrospinning is facile method to fabricate nanofibers with high-throughput performance. However, this process is limited the use of materials such as polymer or polymer-mixed materials with low contents. To come close toward wearable, skin attachable, or injectable electronics, inorganic nanofibers are necessary for realization future electronics as main components, such as electrodes, semiconducting materials, or energy harvesting materials with high performances and mechanical properties. For this reason, we suggested the coaxial electrospinning process with inorganic nanoparticle inks as a core solution. The polymeric shell solution can be dragged out and guided core solution during the coaxial electrospinning process. After sintering process, polymeric parts can be removed various approaches and inorganic nanofibers can be obtained. First, we fabricated metal nanofibers such as silver nanofibers (AgNFs), copper nanofibers (CuNFs), and nickel nanofibers (NiNFs) using coaxial electrospinning. Combining with twodimensional graphene and random networks of electrospun silver nanofibers (AgNFs) has low sheet resistance (~4 Ω/sq), high total transmittance (93% in visible-ray), and superb mechanical properties. We are convinced that this hybrid nanostructures can be ubstituted ITO and occupied an important position in flexible electronics. For possibility for future electronics, we demonstrate wireless attachable sensor consisted AgNF-graphene on various surfaces. In addition, we demonstrated AgNF embedded structures. Specific applications, which are required relatively low surface roughness (below 10 nm), are limited due to metal NFs’ roughness. To overcome these issues, we demonstrate metal nanofiber embedded structures and organic light emitting device (OLED) is successfully demonstrated. Second, four different types of nanostructured carbon nanofibers (CNFs), plain, hollow, multichannel (MC), and hollowed MC, were fabricated using coaxial lectrospinning and thermal treatment for supercapacitor electrodes. The influence of the porosity on the specific surface area (SSA), pore volumes, and electrochemical propoerties of nanostructured CNFs were investigated. Also, their hybrid structures with multi-walled carbon nanotubes (MWCNTs) was analyzed in therms of their porosity, SSA, and electrochemical properties for supercapacitors (specific capacitance and long-term cycling). These hybrid structures can improve overall porosity and lectrochemical propoerties due to the extra mesoporous structures formed by entangling MWCNTs. In conclusion, these anostructured CNFs have a promising potential for various fields which need high porosity and SSA, and can be used as the platforms for catalysis, sensors, or energy devices. We demonstrate the nanofiber-based energy device and wearable devices, such as skinattachable gas sensor, flexible and transparent heater. Nanofiber is one of promising materials for future electronics and substantial progress towards producing wearable electronics.