ABSTRACT
Dispersion, distribution, and surface properties of different nanomaterials are among the most important factors that affect properties and functionalities of polymer nanocomposites. Therefore, a great amount of effort has been made to realize high-level uniform dispersion and precisely controlled distribution and surface properties of nanomaterials, in order to obtain desired dielectric properties, as discussed in the previous chapters.In addition to these efforts on a traditional composites, there are many new nanocomposite structures providing much potential for enhanced dielectric performances, thanks to the fast development of materials chemistry and physics, nanotechnology, and polymer processing techniques [2, 3, 5-10, 12, 14-17, 20, 22, 24-32, 34-40, 42-48, 51-69]. The most popular and successful new structures
are polymer nanocomposites with hybrid nanomaterial systems. Hybrid polymer nanocomposites not only have improved dielectric permittivity and energy storage capability for the polymer matrices, but have also shown incredible effectiveness in preventing large increase in energy loss. These unconventional nanocomposites have more complex structures and compositions. In addition, this complexity also provides more controllable structural and material parameters for the customization of dielectric properties. 8.1 Hybrid Systems with Isolated Nanomaterials Hybrid nanomaterials systems consist of more than one type of nanomaterials or nanostructures. A certain synergy between different nanomaterials in the same system is typically expected, in order to achieve properties better than those of the traditional nanocomposites [23]. By directly mixing a polymer matrix with different types of nanomaterials, a hybrid polymer nanocomposite structure can be simply fabricated. A common synergistic effect is the improvement of dispersion quality of nanomaterials, leading to enhancement in the properties and functionalities. However, the understanding of this effect is very limited today.Figure 8.1 is an example of polymer nanocomposites made by directly mixing BaTiO3 nanoparticles (NBTs) and multiwalled carbon nanotubes (MWCNTs) with PVDF [6]. It is clear that the phase structures of this ternary polymer nanocomposite were related to the compositions. The resulting dielectric properties showed a visible dependence on the concentrations of both NBTs and MWCNTs. In particular, at a volume fraction of 0.02 MWCNT, a high dielectric constant was achieved, regardless of the concentration of NBTs. At the same time, it was found that the dielectric loss was mostly from conduction loss. This composition-dependent dielectric constant could be understood by the evolution of the network structures of MWCNTs and NBTs in PVDF matrix with the variation of the compositions. According to the TEM images in Fig. 8.1, the dispersion of MWCNTs was improved with the addition of NBTs. In particular, the high volume fraction of NBTs seemed to benefit the dispersion of MWCNTs by individualizing bundled MWCNTs and
favor the formation of the MWCNT network. The uniform dispersion leads to a large number of microcapacitor structures shown in the dashed circles in Fig. 8.1. Similar isolating effects of NBTs were also found in the PVDF/graphene/NBT nanocomposites [41].
