ABSTRACT
Many workers in the field of nanodielectrics, or more generally nanocomposites, have suggested that the key to understanding these systems lies at the interface between nanoparticle and matrix. The argument is that local interactions will define both the structure and molecular dynamics in consequent interphase regions. Along with the processing methodology, this will then determine the distribution of the nanoparticles throughout the bulk. Generic terms like “polyethylene” or “epoxy resin” cover a vast array of different molecular forms and microstructures, resulting in different material properties, depending on various factors like, for example, the processing temperature. As an example, there are more than 50 compounds that fit the definition of epoxy resin, which can be combined with several hundred types of hardener [1, 2]. Polyethylene is also not limited to varying degrees of cross-linking, but can exhibit various crystalline structures spanning the size range of nanometers to micrometers [3]. When surface modified, nanometric particles of varying aspect ratios are added to the mix, the terminology “nanodielectric” gets
even fuzzier. However, in the literature it is often assumed that nanocomposites must contain inorganic filler particles in order to be classified as such. The definition of “nanoparticle” is equally vague. It is generally accepted, that engineered materials with at least one dimension smaller than 100 nm are considered nanofillers. This includes such diverse structures as spherical nanosilica, graphene sheets, nanoscale rods or urchin-like structures that are created by RAFT methods. A series of questions needs to be answered, in order clearly to define such a composite material built from a combination of such diverse components. Questions like: what is the size distribution of the particles? How well dispersed are the particles in the polymer matrix? What is the inter-particle distance, i.e., the average distance between neighboring particles? How large are the agglomerates and how many are there? A good particle dispersion does not guarantee a good particle distribution (see Fig. 5.1). What is the surface chemistry of the particles and how does it affect the polymer? Are there by-products left in the polymer from the manufacturing process? All these and many other factors affect the dielectric performance of nanostructured materials, albeit it is not always clear to what extent [4]. A wide range of different techniques are therefore relevant to characterize these systems.
