Issue 46, 2015

Interplay between solid state transitions, conductivity mechanisms, and electrical relaxations in a [PVBTMA] [Br]-b-PMB diblock copolymer membrane for electrochemical applications

Abstract

Understanding the structure–property relationships and the phenomena responsible for ion conduction is one of the keys in the design of novel ionomers with improved properties. In this report, the morphology and the mechanism of ion exchange in a model anion exchange membrane (AEM), poly(vinyl benzyl trimethyl ammonium bromide)-block-poly(methylbutylene) ([PVBTMA][Br]-b-PMB), is investigated with small angle X-ray scattering, high-resolution thermogravimetry, modulated differential scanning calorimetry, dynamic mechanical analysis, and broadband electrical spectroscopy. The hyper-morphology of the material consists of hydrophilic domains characterized by stacked sides of [PVBTMA][Br] which are sandwiched between “spaghetti-like” hydrophobic cylindrical parallel domains of the PMB block. The most important interactions in the hydrophilic domains occur between the dipoles of ammonium bromide ion pairs in the side chains of adjacent chains. A reordering of the ion pair dipoles is responsible for a disorder–order transition (Tδ) at high temperature, observed here for the first time in AEMs, which results in a dramatic decrease of the ionic conductivity. The overall mechanism of long range charge transfer, deduced from a congruent picture of all of the results, involves two distinct ion conduction pathways. In these pathways, hydration and the motion of the ionic side groups are crucial to the conductivity of the AEM. Unlike the typical perfluorinated sulfonated proton-conducting polymer, the segmental motion of the backbone is negligible.

Graphical abstract: Interplay between solid state transitions, conductivity mechanisms, and electrical relaxations in a [PVBTMA] [Br]-b-PMB diblock copolymer membrane for electrochemical applications

Supplementary files

Article information

Article type
Paper
Submitted
16 Sep 2015
Accepted
16 Oct 2015
First published
16 Oct 2015

Phys. Chem. Chem. Phys., 2015,17, 31125-31139

Author version available

Interplay between solid state transitions, conductivity mechanisms, and electrical relaxations in a [PVBTMA] [Br]-b-PMB diblock copolymer membrane for electrochemical applications

V. D. Noto, G. A. Giffin, K. Vezzù, G. Nawn, F. Bertasi, T. Tsai, A. M. Maes, S. Seifert, E. B. Coughlin and A. M. Herring, Phys. Chem. Chem. Phys., 2015, 17, 31125 DOI: 10.1039/C5CP05545H

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