Charge Behavior at Interfaces Involving Nanocomposites J.C. Pandey and Nandini Gupta Department of Electrical Engineering Indian Institute of Technology Kanpur, Kanpur, India ABSTRACT A major disadvantage of polymeric insulation is space charge accumulation at high dc electric fields. Space charge is associated with degradation and premature failure of polymeric insulation through distortion of electric fields. Polymer nanocomposites or nanodielectrics have emerged as a class of novel dielectric materials with improved material properties. We are therefore, looking at an increased use of nanocomposites in the near future. Additionally, we expect nanocomposites to be used in conjunction with conventional insulating materials, thus giving rise to interfaces. Interfaces are important because they often cause accumulation of interfacial charge or space charge with its attendant issues. The present work studies space charge behavior in nanocomposites and its interfaces with other materials. The space charge distribution is mapped using a Pulsed Electro-Acoustic (PEA) system. Polarization-depolarization current measurements are also performed. Measurements are performed under different experimental conditions (electric field, aging etc.). Experimental data indicate that nanoparticles affect charge injection as well as charge transport through change in interfacial and bulk properties. Further, thermal aging causes significant increase in charge injection and charge transport through the material. Experiments with as-received and surface-treated nanoparticles indicate that surface treatment affects the interphase significantly. Index Terms — Interface, epoxy resin, nanocomposites. 1 INTRODUCTION NANOCOMPOSITES formed by the incorporation of a small fraction of nanometric sized fillers in a base polymer have often shown marked improvement in mechanical, thermal and electrical properties with respect to the base polymer [1-5]. Improvement in various properties like breakdown strength, tree retardation, and partial discharge resistance has been widely reported [6-9]. However, the understanding of charge transport and trapping phenomena in nanocomposites is inadequate, and the available literature lacks consensus [10- 11]. Traditionally, thin dielectric systems employ multilayer formulations to obtain high dielectric strength [12]. Multilayer thin film insulation is used in high voltage capacitors, electrical machines, transformers etc. However, inhomogeneous electric fields at conductor-dielectric interfaces are often found to degrade the material due to partial discharge (PD). Owing to multifunctional features (e.g. flame resistance, mechanical strength, resistance to erosion due to electrical discharge, and thermal stability) exhibited by nanocomposites, multi-dielectric systems involving nanocomposites appear attractive [13]. However, formation of interfaces is unavoidable in multi-dielectric systems. Interfaces often cause accumulation of interfacial charge which aggravates material deterioration through electric field distortion. Investigation of space charge behavior in novel materials like polymer nanocomposites is crucial for the assessment of their suitability in homogenous and multi- dielectric systems. To ensure reliable operation and service life of an insulation system, its aging behaviour needs to be studied. Space charge constitutes an important cause of material degradation [14], and can also serve as an aging marker [15]. In this work, we study the behaviour of charge at interfaces in epoxy-based multi-dielectric systems involving nanocomposites. The space charge studies include analysis of charge behavior in homogenous and multi-dielectric systems before and after thermal aging. Nanocomposites are synthesized using as-received and surface-treated nanoparticles. Surface treatment of nanoparticles is carried out using 3-glycidoxypropyl-trimethoxysilane (GPS) obtained from Sigma Aldritch, USA. Nanoparticle dispersion in epoxy is examined using Field Emission Scanning Electron Microscopy (FESEM). The Pulse Electro Acoustic (PEA) technique is used to map space charge along the thickness of the material. Conduction current measurements are also performed to understand the role of nanoparticles in charge trapping and conduction phenomena. Homogenous and multi- layered dielectrics are thermally aged for different times to study the effect of aging on space charge and conduction 0DQXVFULSW UHFHLYHG RQ  0DUFK  LQ ILQDO IRUP  6HSWHPEHU  DFFHSWHG  2FWREHU  &RUUHVSRQGLQJDXWKRU 1 *XSWD IEEE Transactions on Dielectrics and Electrical Insulation Vol. 25, No. 1; February 2018 73 DOI: 10.1109/TDEI.2018.006710