Improved mechanical dispersion or use of coupling agents? Advantages and disadvantages for the properties of fluoropolymer/ceramic composites

The aim of this work is to investigate the influence of interfacial chemistry on the properties of fluoropolymer composites, independent of effects derived from changes in morphology, in particular particle dispersion state. A comparative study of solvent cast composites of poly (vinylidene fluoride – trifluoroethylene) with barium titanate particles, at concentrations up to 60 vol%, was carried out using pristine hydrophilic particles, and particles hydrophobized with three organosilanes, bearing different functional groups (eCH3, eCH2NH2 and eCF3). For each filler concentration, composites with good particle dispersion and comparable amount of porosity with all types of particles were prepared and characterized. While pristine particles provided higher permittivity, all silanes decreased the dielectric losses due to Maxwell-Wagner-Sillars dispersion, although to different extents. Moreover, only the aminosilane provided better thermomechanical stability to the highly filled composites. These results provide useful insights into the advantages and disadvantages of the use of different approaches to improve the dispersion of hydrophilic particles in poly (vinylidene fluoride) copolymer based composites.