Understanding How Metal–Ligand Coordination Enables Solvent Free Ionic Conductivity in PDMS

Abstract

Ionically conductive polymers are commonly made of monomers containing high polarity moieties to promote high ion dissociation, like poly(ethylene oxide) (PEO), polyvinylidene difluoride (PVDF), and poly(vinyl alcohol) (PVA). However, the glass transition temperatures (Tg) of these polymers are relatively high, and therefore, these polymers are in a glassy state at room temperature, which limits the mechanical flexibility of the material. Although polydimethylsiloxane (PDMS) has many attractive physical and chemical properties, including a low glass transition temperature, mechanical flexibility, and good biocompatibility, its low dielectric constant suppresses ion dissociation. In this Letter, we overcome this shortcoming by functionalizing the PDMS with ligands that can form labile coordination with metal ions, which greatly promotes ion dissociation and improves the ionic conductivity by orders of magnitude. By combining an experimental study with a fully atomistic molecular dynamics simulation, we systematically investigated the ion transport mechanisms in this low Tg material.