Poly(siloxane) Derived Ionosilicone Elastomers Reveal Role of Backbone Dynamics in Ionic Double Layer Formation

Poly(siloxane) ionic liquids (PSILs) are a group of single-ion conducting polymers in which a weakly coordinating ion is covalently bonded to a siloxane backbone. The highly flexible siloxane backbone affords these polymers low glass transition temperatures and high room temperature, solvent-free ion conduction, making them a promising option for ion-mediated devices. Here, highly conductive, crosslinked cationic and anionic PSILs consisting of bulky ionic liquid moieties covalently linked to a poly(mercaptopropylmethylsiloxane) backbone were prepared. The backbone of these crosslinked PSILs can be tuned by copolymerization with acrylate monomers to create PSIL-acrylate hybrid networks with intermediate properties. When two oppositely charged PSIL-acrylate hybrid 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. The more mobile networks (i.e., more PSIL content) were able to rectify current at higher frequencies in response to a constant DC overpotential. Interestingly, the capacitive nature of the IDL under reverse biases was diminished with increasing temperature, elucidating the importance of interfacial polymer dynamics on heterojunction performance.