Synthesis and characterization of bicontinuous cubic poly(3,4-ethylene dioxythiophene) gyroid (PEDOT GYR) gels

Abstract

We describe the synthesis and characterization of bicontinuous cubic poly(3,4-ethylenedioxythiophene) (PEDOT) conducting polymer gels prepared within lyotropic cubic poly(oxyethylene)₁₀ nonylphenol ether (NP-10) templates with Iad (gyroid, GYR) symmetry. The chemical polymerization of EDOT monomer in the hydrophobic channels of the NP-10 GYR phase was initiated by AgNO₃, a mild oxidant that is activated when exposed to ultraviolet (UV) radiation. The morphology and physical properties of the resulting PEDOT gels were examined as a function of temperature and frequency using optical and electron microscopy, small-angle X-ray scattering (SAXS), dynamic mechanical spectroscopy, and electrochemical impedance spectroscopy (EIS). Microscopy and SAXS results showed that the PEDOT gels remained ordered and stable after the UV-initiated chemical polymerization, confirming the successful templated-synthesis of PEDOT in bicontinuous GYR nanostructures. In comparison to unpolymerized 3,4-ethylenedioxythiophene (EDOT) gel phases, the PEDOT structures had a higher storage modulus, presumably due to the formation of semi-rigid PEDOT-rich nanochannels. Additionally, the storage modulus (G′) for PEDOT gels decreased only modestly with increasing temperature, from ∼1.2 × 10⁵ Pa (10 °C) to ∼7 × 10⁴ Pa (40 °C), whereas G′ for the NP-10 and EDOT gels decreased dramatically, from ∼5.0 × 10⁴ Pa (10 °C) to ∼1.5 × 10² Pa (40 °C). EIS revealed that the impedance of the PEDOT gels was smaller than the impedance of EDOT gels at both high frequencies (PEDOT ∼10² Ω and EDOT 2–3 × 10⁴ Ω at 10⁵ Hz) and low frequencies (PEDOT 10³–10⁵ Ω and EDOT ∼5 × 10⁵ Ω at 10⁻¹ Hz). These results indicated that PEDOT gels were highly ordered, mechanically stable and electrically conductive, and thus should be of interest for applications for which such properties are important, including low impedance and compliant coatings for biomedical electrodes.