Poly(siloxane)-Derived Ionosilicone Elastomers Reveal the Role of Interfacial Polymer Dynamics in Ionic Double-Layer Rectification

Poly(siloxane ionic liquid)s (PSILs) have highly flexible siloxane backbones, affording them low glass transition temperatures and therefore high solvent-free ionic conductivity at ambient temperature, offering promise for ion-mediated electronic devices. Here, cross-linked, highly conductive (>4 × 10^-3 mS/cm) cationic and anionic PSILs (termed ionosilicones) were prepared. The backbone of these ionosilicone networks could be tuned by copolymerization with acrylate monomers to create ionosilicone-acrylate hybrid networks with intermediate properties. When two oppositely charged networks are brought into contact, an ionic double layer (IDL) consisting of fixed cations and anions is formed, and the heterojunction exhibits diode-like nonlinear conductance and ionic current rectification. Interestingly, we observe a trade-off between IDL polarization speed and rectification performance with increased ionosilicone content. We show that the more rapid interfacial polymer dynamics induced by increasing temperature switches the diode "on" in a similar manner as applying a forward DC bias voltage. To explain this multimodal switching behavior, we posit the formation of an interfacial complex with distinctly slower dynamics than the bulk, low-<i>T</i>_g ionoelastomers, limiting ion motion at low temperatures and under reverse bias. These findings provide insight into the key role of backbone flexibility of IDL-based device performance and shine new light on interfacial polymer dynamics as an important design criterion in bipolar ionotronic devices.