Fundamentals for the compounding of nanocomposites to enhance electrical insulation performance

Although it is undeniable that the promise of enhanced dielectric properties through the use of nanotechnology has generated worldwide interest in nanodielectrics in the last decade, study of the experimental literature indicates that there are numerous inconsistencies in the results obtained. In many instances, it is likely that this is due to a lack of quality control during the formulation of this new class of material. By examining several nanocomposite examples, this contribution seeks to shed some light on the likely causes for these inconsistencies. Through the paramount property of dielectric strength, it is confirmed that poor dispersion and/or agglomeration is often the cause of poor material performance. Examples are provided to show how this can be rectified through the use of particle functionalization and compatibilizers, the use of shear in compounding, and the careful control of moisture. However, good dispersion alone is not sufficient since some of the techniques used may also lead to microcavity formation and other undesirable phenomena. The optimization of nanocomposite compounding is intimately connected with the need to quantify the resulting structure. Consequently, the paper includes a brief discussion of the part played by thermogravimetric and thermal analyses as well as the use of the focused ion beam method to supplement scanning electron microscopy as a viable alternative to (the more difficult) transmission electron microscopy for the evaluation of dispersion and percolation.