3405 © 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com Enhanced Dielectric Performance in Polymer Composite Films with Carbon Nanotube-Reduced Graphene Oxide Hybrid Filler Jin-Young Kim, TaeYoung Kim, Ji Won Suk, Harry Chou, Ji-Hoon Jang, Jong Ho Lee, Iskandar N. Kholmanov, Deji Akinwande, and Rodney S. Ruoff* 1. Introduction Polymer-based dielectric films have been considered for use in electroluminescent devices, gate dielectrics, electrical energy storage, and touch panel devices due to their high DOI: 10.1002/smll.201400363 The electrical conductivity and the specific surface area of conductive fillers in conductor-insulator composite films can drastically improve the dielectric performance of those films through changing their polarization density by interfacial polarization. We have made a polymer composite film with a hybrid conductive filler material made of carbon nanotubes grown onto reduced graphene oxide platelets (rG-O/CNT). We report the effect of the rG-O/CNT hybrid filler on the dielectric performance of the composite film. The composite film had a dielectric constant of 32 with a dielectric loss of 0.051 at 0.062 wt% rG-O/CNT filler and 100 Hz, while the neat polymer film gave a dielectric constant of 15 with a dielectric loss of 0.036. This is attributed to the increased electrical conductivity and specific surface area of the rG-O/CNT hybrid filler, which results in an increase in interfacial polarization density between the hybrid filler and the polymer. Carbon Nanotubes Dr. J.-Y. Kim, H. Chou, Dr. J.-H. Jang, Dr. I. N. Kholmanov, Prof. R. S. Ruoff Department of Mechanical Engineering and The Materials Science and Engineering Program The University of Texas at Austin Austin, TX 78712, USA E-mail: r.ruoff@mail.utexas.edu Prof. T. Y. Kim Department of Bionanotechnology Gachon University Seongnam 461–701, Republic of Korea Prof. J. W. Suk School of Mechanical Engineering Sungkyunkwan University Suwon 440–746, Republic of Korea J. H. Lee, Prof. D. Akinwande Department of Electrical and Computer Engineering Microelectronics Research Center The University of Texas at Austin Austin, TX 78758, USA flexibility, low temperature processing conditions, and simple fabrication process. [1–3] However, these polymer films gen- erally have low dielectric constants, and thus yield low per- formance in electronic devices. One strategy to increase the dielectric constant of polymer dielectric films is to use ferro- electric ceramic (e.g., barium titanate or strontium titanate) and/or electrically conductive fillers (e.g., metal nano-parti- cles or carbon-based nanostructures). Incorporating these fillers in the polymer matrix can increase the capacitance due to the induced interfacial or space charge polarization between the filler and the polymer. [1,4] Carbon-based nanostructures, e.g., carbon nanotubes (CNTs) and graphene, have attracted much attention for electrical device applications, such as transparent conductive films, field-effect transistors, field emitters, electrolumines- cent devices, and supercapacitors, owing to their electrical and mechanical properties. [2,5–9] Recently, these nanostruc- tures have been considered for high-k dielectric composite film applications. Polymer composite films containing CNTs or graphene as conductive fillers have been studied to try and achieve high dielectric performance. [10–15] As was men- tioned above, incorporating a conductive filler (e.g., CNT or reduced graphene oxide (rG-O)) in a polymer composite can, in the presence of an applied electric field, also induce an interfacial or space charge polarization in the composite film when below its percolation threshold concentration, small 2014, 10, No. 16, 3405–3411