Interdisciplinary Approaches towards Materials with Enhanced Properties for Electrical Engineering

The internationally growing demand for electrical energy is one of the most prominent triggers stimulating research these days. In this highly interdisciplinary research area, electrical engineers, material scientists and chemists collaborate for the design and fabrication of the next generation of high-voltage machinery and electro-technical devices. Nanocomposites with enhanced thermal conductivity and improved electric properties are in the center of these joint research activities. Hence, in this Special Issue of the open-access journal Polymers, the state-of-the-art research and technology of the area ‘microand nanocomposites for electrical engineering applications’ has been summarized in three review articles, while the current research trends and the development and characterization of novel materials have been described in eight original research articles. State-of-the-art of research and technology. The comprehensive review article by Plesa et al. addresses with dedication the structure-property relationships of composite materials with special respect to their electric properties and the resulting potential application fields [1]. Originating from the high demands regarding the reliability and lifetime expectance of high-voltage engineering machineries such as generators and transformers, the mechanical properties of insulating resins and the corresponding microand nanocomposites are of prime importance; this topic has been summarized in the review article by Moser and Feuchter [2], in which epoxy-based resins are discussed in detail. Mica/epoxy composites are the most commonly used insulation materials in high-voltage rotating machines, and their properties as well as the possibly occurring failure mechanisms of the composite material have been described in the review article by Andraschek and colleagues [3]. Novel composites based on epoxy resins or on low-density polyethylene. The preparation as well as the isotropic electrical properties (in the case of additionally present silver nanowires) of epoxy-based nanocomposites containing in-situ formed silver nanoparticles was reported by Kang, Lee, and Song [4]. Vaughan and Yeung described the effect of siloxane-mediated surface functionalization of silica nanoparticles [5]; the corresponding epoxy-based nanocomposites exhibited breakdown strengths that were increased by approx. 50% compared to the unfilled epoxy resin. Gubanski et al. reported the decrease of the direct current conductivity of low-density polyethylene composites containing inorganic fillers such as magnesium oxide and aluminum oxide [6]. In a subsequent study [7], a bipolar charge transport model was employed to investigate this reduction, from which the reduced charge injection at electrodes was identified as the most important parameter causing the observed effects. Materials based on polymers from renewable resources and composites based on (per-) fluorinated polymers. Smit, Wiesbrock et al. reported the synthesis of crosslinkable copoly(2-oxazoline)s from fatty acids such as castor oil and coconut oil [8]. The crosslinked copolymers exhibited electric properties similar to those of polyamides, which renders them medium insulators. The in-situ preparation of reduced graphene oxide/carboxymethyl chitosan composites was described by Luo, Chen, and colleagues [9].