Effect of Chain Rigidity on the Decoupling of Ion Motion from Segmental Relaxation in Polymerized Ionic Liquids: Ambient and Elevated Pressure Studies

Abstract

Conductivity in polymer electrolytes has been generally discussed with the assumption that the segmental motions control charge transport. However, much less attention has been paid to the mechanism of ion conductivity where the motions of ions are less dependent (decoupled) on segmental dynamics. This phenomenon is observed in ionic materials as they approach their glass transition temperature and becomes essential for design and development of highly conducting solid polymer electrolytes. In this paper, we study the effect of chain rigidity on the decoupling of ion transport from segmental motion in three polymerized ionic liquids (polyILs) containing the same cation−anion pair but differing in flexibility of the polymer backbones and side groups. Analysis of dielectric and rheology data reveals that decoupling is strong in vinyl-based rigid polymers while almost negligible in novel siloxane-based flexible polyILs. To explain this behavior, we investigated ion and chain dynamics at ambient and elevated pressure. Our results suggest that decoupling has a direct relationship to the frustration in chain packing and free volume. These conclusions are also supported by coarse-grained molecular dynamics simulations.

Polymerized ionic liquids: Effects of counter‐anions on ion conduction and polymerization kinetics

“…S6, Supporting Information). We attributed the remaining conductivity difference after normalization of mobility to the additional effects such as decoupling of segmental dynamics from the counter‐ion dynamics . This trend agrees well with PILs in which ionic groups are separated from the polymer backbone .…”

Structural and Mechanical Properties of Ionic Di-block Copolymers via a Molecular Dynamics Approach

“…Figure 4 demonstrates density versus temperature relation of both HPs and di-BCPs with varying charge ratio. Glass transition temperature (Tg) can be obtained by the change in the thermal expansion coefficient [32,33,34]. Tg of both charged HPs and BCPs gradually increase with charge ratio.…”

Decoupling segmental relaxation and ionic conductivity for lithium-ion polymer electrolytes

“…91 Correlating the degree of decoupling with the flexibility (i.e., the fragility) of the poly(IL) electrolyte by comparing the relatively rigid vinyl-based poly(IL)s and the rather flexible siloxanetype poly(IL)s, confirmed that there is a direct relationship between the chain packing frustration (due to the polymer fragility) and the decoupled ionic motion within the resulting free volume. 92 As a matter of fact, the authors observed a decreased decoupling under elevated pressure, especially for rather flexible poly(IL)s. For rigid poly(IL) electrolyte, however, this effect was less pronounced, highlighting the importance of the free volume.…”