Effect of the Mixing on the Dielectric Constant of Poly(vinylidene fluoride)/Isotactic Polypropylene Blends

In this work, the effect of a mixing process on the dielectric constant (epsilon) of a typical immiscible blend, poly(vinylidene fluoride) (PVDF)/isotactic polypropylene (iPP), is investigated. An iPP with a relatively low epsilon (ca. 3.4) is added to a PVDF matrix with a relatively high epsilon (ca. 9.5) to reduce the 8 of the system. The blend has a narrow window of cocontinuity (volume fraction of iPP (v(iPP)) of ca. 50-80 vol%). All of the measured epsilon values for the blends lie within the two limits defined by the parallel alignment and series alignment models, which are the upper and lower limits, respectively. It is found that for blends with v(iPP) of ca. 39.7 vol%, for which PVDF is the continuous matrix and iPP is the dispersed phase, prolonging mixing time and adding compatibilizer cause a monotonic decrease of epsilon for the system, which can be attributed to the increasing dispersion of the low-epsilon iPP filler in the high-epsilon PVDF matrix. Based on these results, a strategy to tune the epsilon of polymer blends and composites is discussed. It is suggested that architecture similar to a series alignment will favor the decrease of epsilon, while architecture similar to a parallel alignment will favor the increase of epsilon.