High-dielectric paper composite consisting of cellulose nanofiber and silver nanowire

High-dielectric materials have played essential roles in various electronic applications such as capacitor, transistor, antenna and pressure sensor. In recent years, paper has attracted much attention as a potential substrate for low-cost flexible electronics. However, the dielectric constant (k) of conventional paper is low due to the high porosity of paper and the low k value of air (k≈1). Here we demonstrate the fabrication of high-dielectric and flexible paper nanocomposites. Cellulose pulp fibers with micrometer-scale width were mechanically downsized to nanofibers, and the nanofibers were fabricated into paper, denoted nanopaper in this study. While the conventional paper made from the original pulp fibers had low density (0.72 g cm^-3) and low k value (2.9) at 1.1 GHz, the nanopaper demonstrated high density (1.30 g cm^-3) derived from a densely-packed nanostructure, leading to increase in the k value up to 5.3. In addition, the small amount of conductive silver nanowires (2.54 vol%) were mixed with the nanopaper while avoiding the formation of the percolation network. The resulting silver nanowire/nanopaper composite with paper-specific flexibility achieved extremely high k value (726.5 at 1.1 GHz), and thus is expected as a promising substrate for future flexible electronics.