Electron. Mater. Lett., Vol. 11, No. 2 (2015), pp. 225-231 Dielectric Spectroscopy of High Aspect Ratio Graphene-Polyurethane Nanocomposites Rahim Jan, * Amir Habib, Hina Abbassi, and Shahid Amir School of Chemical & Materials Engineering (SCME), National University of Sciences & Technology (NUST), H-12 Campus, Islamabad, 44000, Pakistan (received date: 30 August 2014 / accepted date: 30 October 2014 / published date: 10 March 2015) 1. INTRODUCTION In recent times, polymeric nanocomposites (PNCs), based on the conductive inclusions, are drawing considerable interest for their potential use in electronic engineering. [1] Graphene, owing to its extraordinary electrical properties, is one such conducting filler, which has been extensively studied for tuning the electrical properties of polymers. [2,3] Apart from many other applications, [4,5] graphene has been imparted to the polymers for the investigation of dielectric characteristics of nanocomposites. [6-9] Owing to the zero band gap of graphene, it is a suitable candidate for radio frequency device applications. [10] Another critical application of graphene/PNCs is energy storage for advanced tech- nologies. The electrical energy density, (U e = , directly depends on relative permittivity ε r and electric field. [11] For PNCs, the dielectric constant can be increased by adding ceramic fillers to it. [12] However, a high ceramic filler loading (beyond 50% vol) is required to considerably increase the dielectric constant. [13] Also, with the increase of filler loading, the mechanical characteristics of the nanocomposites suffer a decline. The last few years have seen a revival in the study of polymers reinforced by two- dimensional fillers, especially graphene due to its exceptionally high modulus (Y ≈ 1 TPa) and strength (σ B ≈ 130 GPa). [14] It has been notably shown that graphene is employed to provide reinforcement at close to the theoretical maximum. [15] Graphene, with its zero band gap structure, possesses high carrier mobility at room temperature (≈10 000 cm 2 V -1 s -1 ) and a large theoretical specific surface area (2630 m 2 g -1 ). These mechanical and electrical characteristics of graphene make it an ideal choice for enhancement of such properties in PNCs. [16] Graphene has been added to various polymers and reported for a low percolation threshold in most of these polymers. [17] Recently, we have studied a very low percolation threshold (0.55%vol GNS) for graphene nanosheets (GNS) dispersed in thermoplastic polyurethane (TPU) nanocom- posites to be published elsewhere. The formation of conducting network in nanocomposites at such low volume fractions is attributed to various reasons like: (1) large surface-to-volume ratio, (2) morphology, (3) dimensions, and (4) dispersion of High aspect ratio graphene nanosheets (GNS), prepared via liquid exfoliation, are homogeneously dispersed in thermoplastic polyurethane (TPU). Dielectric spectroscopy results are reported for these nanocomposites (up to 0.55 vol. % GNS) in the frequency range of 100 Hz to 5 MHz. The as-prepared GNS increased the AC conductivity 10 - 1000 times across the given frequency range. The dielectric constant is increased 5 - 6 times at 100 Hz for the maximum loading of GNS when compared with the pristine TPU, with subsequently high dielectric loss making them a suitable candidate for high energy dissipation applications such as EMI shielding. The temperature effects on the dielectric characteristics of 0.55 vol. % GNS/ TPU nanocomposites beyond 400 K are more pronounced due to the interfacial and orientation polarization. Mechanical characteristics evaluation of GNS/TPU composites shows a marked increase in the ultimate tensile strength without compromising their ductility and stiffness. Keywords: dielectric spectroscopy, polarization, liquid exfoliation, mechanical charateristics ½ε 0 ε r E 2 ) DOI: 10.1007/s13391-014-4265-5 *Corresponding author: rahimjan@scme.nust.edu.pk ©KIM and Springer