Interfacial Effects on Dielectric Propertiesof Polymethylmethacrylate-TitaniaMicrocomposites and Nanocomposites

Abstract

It is discussed that dielectric properties of polymethylmethacrylate (PMMA) composites are influenced by the particle size of titania as a result of changes in the structure and dynamics of polymer chains in the interphase regions around the particles. It is hypothesized that a loosely packed interphase layer, resulted from high stiffness and high cohesion energy of PMMA chains, provides enough free volume for segmental chain movements and dipole orientation along the applied electric field and causes an increase in dielectric properties of nanocomposites at low filler contents. It is shown that the attraction of PMMA toward micro-titania and nano-titania is similar by measuring the surface energy of fillers. Dynamics of polymer chains around fillers is investigated by dynamic-mechanical-thermal analysis and broadband-dielectric spectroscopy, and presence of a loosely packed layer is confirmed by measuring thermal and mechanical glass transition temperature of composites. It is concluded that the anomalous enhancement in dielectric properties of 2 vol% nanocomposite, compared to the corresponding microcomposite, can be attributed to the higher volume fraction of loosely packed interphase layers in the nanocomposite. POLYM. COMPOS., 38:1158–1166, 2017. © 2015 Society of Plastics Engineers