Biphasic Polymer Blends Containing Carbon Nanotubes: Heterogeneous Nanotube Distribution and its Influence on the Dielectric Properties
Résumé
Electrically percolative composites with high dielectric permittivity are currently finding increasing interest in academic and industrial research. They are essential for designing new energy-storage capacitors and electromagnetic interference shielding devices. Herein, we report a percolative multiwalled carbon nanotube (MWNT) filled low density polyethylene (LDPE)/poly(vinylidene fluoride) (PVDF) composite. As compared to the MWNT-filled single LDPE composites, this biphasic polymer composite displays a significantly reduced percolation threshold (9.6 f 5.7 vol %) but still maintains a high permittivity level to reach (∼500). This can be attributed to a double percolated structure observed on the basis of morphological evidence. MWNTs are selectively localized in LDPE phase during melt-mixing. This is contrary to the wetting coefficient evaluation yet still possible when the colossal difference in viscosity of two polymers is taken into account. The effect of double percolation on the dielectric properties was well illustrated by revealing the mechanismfor the improved permittivity. A model based on the Lichtenecker rule and percolation theory was established and demonstrated to be effective to predict the dielectric permittivity in biphasic polymer composites.