Relaxation dynamics of poly(ethylene oxide)

TL;DR

This study provides a comprehensive dielectric spectroscopy analysis of poly(ethylene oxide), identifying four distinct relaxation processes and clarifying their molecular origins, which resolves previous conflicting interpretations.

Contribution

The paper offers the first detailed identification and interpretation of four intrinsic relaxation processes in poly(ethylene oxide) using broad-range dielectric spectroscopy.

Findings

Four intrinsic relaxation processes identified

Normal mode linked to global chain motions

Johari-Goldstein relaxation detected in PEO

Abstract

Poly(ethylene oxide) is an important polymer with many applications, e.g., as solid-state electrolyte in batteries. Its relaxation dynamics, characterizing its molecular and submolecular motions, which is relevant for many of these applications, was investigated numerous times, mostly employing dielectric spectroscopy. However, the various dynamic processes revealed by these studies were interpreted in conflicting ways and even their nomenclature in literature is highly inconsistent. Here we present the results of a detailed investigation of this polymer employing dielectric spectroscopy covering a relatively broad frequency and temperature range. We clearly detect four intrinsic relaxation processes. The slowest one most likely represents a so-called normal mode, reflecting global motions of the polymer chains, an interpretation that was not considered in previous works. The second process can be unequivocally identified with the segmental alpha relaxation, which governs glassy freezing and the glass transition. The third, only rarely detected process corresponds to the Johari-Goldstein relaxation of poly(ethylene oxide), widely overlooked in previous studies. The fourth and fastest process is unrelated to the supercooled and glassy state of this polymer and probably due to local, intramolecular motions.