Free Volume Study on the Origin of Dielectric Constant in a Fluorine-Containing Polyimide Blend: Poly(vinylidene fluoride-co-hexafluoro propylene)/Poly(ether imide)

Abstract

The dielectric constant of fluorinated polymides, their blends, and composites is known to decrease with the increase in free volume due to a decrease in the number of polarizable groups per unit volume. Herein, we report an interesting finding on the origin of dielectric constant in a polymer blend prepared using a fluorine-containing polymer and a polyimide probed in terms of its available free volume, which is distinct from the generally observed behavior in fluorinated polyimides. For this study, a blend of poly(vinylidene fluoride-co-hexafluoro propylene) and poly(ether imide) was chosen and the interaction between them was studied using FTIR, XRD, TGA, and SEM. The blend was investigated by positron annihilation lifetime spectroscopy (PALS), Doppler broadening (DB), and dielectric analysis (DEA). With the increase in the free volume content in the blend, surprisingly, the dielectric constant also increases and is attributed to additional space available for the polarizable groups to orient themselves to the applied electric field. The results obtained would pave the way for more effective design of polymeric electrical charge storage devices.

Dielectric and conducting behavior of pyrene functionalized PANI/P(VDF‐co‐HFP) blend

“…Thus, this change is attributed to the dielectric relaxation of PVH on passing its T g . Our recent free volume study on PVH reveals that the dielectric constant in PVH arises mainly due to dipole orientation polarization . Below −40 °C, the PVH is in the glassy phase and hence the molecular motions are frozen in place due to which the dipoles cannot move to align themselves to the applied electric field.…”

“…The corresponding dielectric loss is also high [see Figure (E)]. The glass transition temperature ( T g ) of PVH is −33 °C . Thus, this change is attributed to the dielectric relaxation of PVH on passing its T g .…”

“…This is because, the PVDF‐based polymers have the highest dielectric constant amongst polymers . The incorporation of amorphous phase of hexafluoropropylene (HFP) into the main constituent vinylidene fluoride (VDF) blocks was reported to modify some of the properties of the homopolymer . Particularly, the degree of crystallinity in poly(vinylidene fluoride‐ co ‐hexafluoro propylene) [P(VDF‐ co ‐HFP)] is significantly reduced in comparison with PVDF, while the flexibility and solubility in organic solvents are enormously increased …”

Hyperbranched‐polysiloxane‐based hyperbranched polyimide films with low dielectric permittivity and high mechanical and thermal properties

“…In order to obtain low‐dielectric PI, two strategies are mainly used: (1) decreasing dipole strength or (2) reducing the number of dipoles . It has been reported that the introduction of fluorine atoms into the PI backbone could reduce D k and improve water resistance .…”

“…synthesized perfluorocyclobutyl biphenyl ether‐based PI, which showed low D k (2.43−2.50) upon moisture absorption for 24 h. However, this kind of PI suffers from poor adhesion with metal. Because the D k of air is approximately 1.0, introducing air voids into PI will decrease the dielectric permittivity of PI . These PIs, such as nanoporous PI and PI aerogels, have been extensively studied .…”