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

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), poly(vinyl alcohol) (PVA). However, the glass transition temperature ($T_g$) of these polymers are relatively high, and therefore yields a glassy state at room temperature and limits the mechanical flexibility of the material. Although polydimethylsiloxane (PDMS) has many attractive physical and chemical properties, including low glass transition temperature, mechanical flexibility, and good biocompatibility, its low dielectric constant suppresses ion dissociation. In this paper, we overcome this shortage by functionalizing the PDMS with ligands that can form labile coordination with metal ions, which greatly promotes the 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 $T_g$, low intrinsic conductivity material.