Relaxations and Relaxor-Ferroelectric-Like Response of Nanotubularly Confined Poly(vinylidene fluoride)

TL;DR

This study reveals that PVDF nanotubes confined in AAO templates exhibit relaxor-ferroelectric-like behavior with temperature-independent relaxations and broad dielectric maxima, suggesting formation of ferroelectric nanodomains at interfaces.

Contribution

It demonstrates for the first time that nanotubular PVDF shows relaxor-ferroelectric-like responses due to interfacial effects and nanodomain formation, unlike bulk PVDF.

Findings

Bimodal relaxation process observed in PVDF nanotubes.

Temperature-independent relaxations at high temperatures.

Presence of relaxor-like dielectric maxima.

Abstract

Herein, we elucidate the impact of tubular confinement on the structure and relaxation behaviour of poly(vinylidene difluoride) (PVDF) and how these affect the para-/ferroelectric behavior of this polymer. We use PVDF nanotubes that were solidified in anodic aluminum oxide (AAO) templates. Dielectric spectroscopy measurements evidence a bimodal relaxation process for PVDF nanotubes: besides the bulk-like -relaxation, we detect a notably slower relaxation that is associated with the PVDF regions of restricted dynamics at the interface with the AAO pore. Strickingly, both the bulk-like and the interfacial relaxation tend to become temperature independent as the temperature increases - a behavior that has been observed before in inorganic relaxor ferroelectrics. In line with this, we observe that the real part of the dielectric permittivity of the PVDF nanotubes exhibits a broad maximum when plotted against the temperature, which is, again, a typical feature of relaxor ferroelectrics. As such, we propose that in nanotubular PVDF, ferroelectric-like nanodomains are formed in the amorphous phase regions adjacent to the AAO interface. These ferroelectric nanodomains may result from an anisotropic chain conformation and a preferred orientation of local dipoles due to selective H-bond formation between the PVDF macromolecues and the AAO walls. Such relaxor-ferroelectric-like behaviour has not been observed for non-irradiated PVDF homopolymer; our findings thus may enable in the future alternative applications for this bulk commodity plastic, e.g., for the production of electrocaloric devices for solid-state refrigeration which benefit from a relaxor-ferroelectric-like response.