High Dielectric Performances of Flexible and Transparent Cellulose Hybrid Films Controlled by Multidimensional Metal Nanostructures

• Published in: Advanced materials (Weinheim) Vol. 29; no. 24
• Main Authors: Ji, Sangyoon, Jang, Jiuk, Cho, Eunjin, Kim, Si‐Hoon, Kang, Eun‐Seok, Kim, Jihoon, Kim, Han‐Ki, Kong, Hoyoul, Kim, Sun‐Kyung, Kim, Ju‐Young, Park, Jang‐Ung
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.06.2017
• Subjects: Cellulose; Dielectric properties; Electronic devices; Fillers; high dielectric constants; Materials science; metal nanofibers; Modulus of elasticity; Nanofibers; Optical properties; Panels; Permittivity; Polymers; Portable equipment; Sensitivity; Smartphones; Stretching; Tensile strength; Thermal expansion; Thermal stability; Touch; touchscreen panels; Transmittance; transparent films; Wearable technology; metal nanofibers; transparent films; high dielectric constants; cellulose; touchscreen panels
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.201700538

Various wearable electronic devices have been developed for extensive outdoor activities. The key metrics for these wearable devices are high touch sensitivity and good mechanical and thermal stability of the flexible touchscreen panels (TSPs). Their dielectric constants (k) are important for high touch sensitivities. Thus, studies on flexible and transparent cover layers that have high k with outstanding mechanical and thermal reliabilities are essential. Herein, an unconventional approach for forming flexible and transparent cellulose nanofiber (CNF) films is reported. These films are used to embed ultralong metal nanofibers that serve as nanofillers to increase k significantly (above 9.2 with high transmittance of 90%). Also, by controlling the dimensions and aspect ratios of these fillers, the effects of their nanostructures and contents on the optical and dielectric properties of the films have been studied. The length of the nanofibers can be controlled using a stretching method to break the highly aligned, ultralong nanofibers. These nanofiber‐embedded, high‐k films are mechanically and thermally stable, and they have better Young's modulus and tensile strength with lower thermal expansion than commercial transparent plastics. The demonstration of highly sensitive TSPs using high‐k CNF film for smartphones suggests that this film has significant potential for next‐generation, portable electronic devices. Transparent and flexible cellulose films with a high dielectric performance using ultralong metal nanofibers are key attributes for flexible touchscreen panels (TSPs). High‐dielectric‐constant (k) CNF films using ultralong silver nanofibers have outstanding optical transmittance (≈90%) with high‐k values (k = 9.2 at 120 kHz). A TSP that is protected with a high‐k CNF film shows high touch sensitivity.