Dielectric relaxations and conduction mechanisms in polyether–clay composite polymer electrolytes under high carbon dioxide pressure

Abstract

The composite material P(EO/EM)–Sa consisting of synthetic saponite (Sa) dispersed in poly[ethylene oxide-co-2-(2-methoxyethoxy)ethyl glycidyl ether] (P(EO/EM)) is studied by “in situ” measurements using broadband electrical spectroscopy (BES) under pressurized CO₂ to characterize the dynamic behavior of conductivity and the dielectric relaxations of the ion host polymer matrix. It is revealed that there are three dielectric relaxation processes associated with: (I) the dipolar motions in the short oxyethylene side chains of P(EO/EM) (β); and (II) the segmental motion of the main chains comprising the polyether components (α_fast, α_slow). α_slow is attributed to the slow α-relaxation of P(EO/EM) macromolecules, which is hindered by the strong coordination interactions with the ions. Two conduction processes are observed, σ_DC and σ_ID, which are attributed, respectively, to the bulk conductivity and the interdomain conductivity. The temperature dependence of conductivity and relaxation processes reveals that α_fast and α_slow are strongly correlated with σ_DC and σ_ID. The “in situ” BES measurements under pressurized CO₂ indicate a fast decrease in σ_DC at the initial CO₂ treatment time resulting from the decrease in the concentration of polyether–Mⁿ⁺ complexes, which is driven by the CO₂ permeation. The relaxation frequency (f_R) of α_slow at the initial CO₂ treatment time increases and shows a steep rise with time with the same behavior of the α_fast mode. It is demonstrated that the interactions between polyether chains of P(EO/EM) and cations in the polymer electrolyte layers embedded in Sa are probably weakened by the low permittivity of CO₂ (ε = 1.08). Thus, the formation of ion pairs in the polymer electrolyte domains of P(EO/EM)–Sa occurs, with a corresponding reduction in the concentration of ion carriers.