Identification of relaxation processes in pure polyethylene oxide (PEO) films by the dielectric permittivity and electric modulus formalisms

Abstract

The ac‐impedance of bulk‐like films of pure polyethylene oxide (PEO) polymer was measured as a function of frequency f in the range 0.1 to 107 Hz at various constant temperatures T (155 − 330 K). The as‐measured data were analyzed by electric permittivity and modulus formalisms to unveil which dielectric and conductive relaxation processes were responsible for their relaxation behavior below/above glass transition temperature Tg of pure PEO polymer. At T > Tg, none of the α‐, β‐, or γ‐relaxations could be inferred for studied pure PEO films from frequency variation of measured imaginary part ε′′(f, T) of complex dielectric permittivity trueε~(),fT, as low‐frequency losses masked real dielectric contribution to the measured ε′′(f, T) at low frequencies and high temperatures. However, at T < Tg, a broad, relaxation process has been observed in the high‐frequency part of their isothermal ε′′(f, T) − f spectra, which can be related to the β‐ or γ‐dielectric relaxation process. Nonlinear regressions of the measured ε′′(f, T) − f data for T < Tg yielded moral fits to a simple addition of a Havriliak‐Negami function, and a Bergman‐loss Kohlrausch‐Williams‐Watts‐type function, with the relaxation time τmax(T) obtained from Havriliak‐Negami‐fitting parameters, was found to follow a thermally activated Arrhenius‐like relaxation behavior. Conversely, representation of the imaginary part M′′(f, T > Tg) − f spectra of complex electric modulus trueM~()f=1/trueε~()f was found to depict 2 overlapped relaxation processes, which were detached well by a nonlinear regression of a simple superposition of 2 different M′′(f) expressions having the form of the universal Bergman loss function, where it was found that the relaxation time is also thermally activated.

Studies of composite films of polyethylene oxide doped with potassium hexachloroplatinate

“…32 Interestingly, the relaxation time of the PEO/K2PtCl6 in T≲ Tg follows the Arrhenius-like behavior (as seen in Figure 3) similar to that for T g of the pure PEO as prepared by the solution-casting method prepared in to our previous works. 23,33 This behavior is the typical behavior of β-relaxation processes in glass formers polymers 34 such as PEO. Hence, the PEO/K 2 PtCl 6 complex composite behaves similar to the glass forming polymer.…”

“…This modulus dielectric formalism provides extensive insights into the processes of charge transport, such as the mechanism of ion dynamics as a frequency and temperature dependence. In the modulus formalism, an electric modulus is given by: where M ′ and M ″ are the real and the imaginary parts of the complex modulus ( M ′′ ), respectively. 46 The formula can be reformed as: 23 …”

“…where M 0 and M 00 are the real and the imaginary parts of the complex modulus (M 00 ), respectively. 46 The formula can be reformed as: 23 M ω…”

“…Furthermore, the β-relaxation process has to be explored in the meaning of a cooperative segmental motion in the noncrystalline part or the "interphase" between the crystalline and the amorphous segments of the PEO/K 2 PtCl 6 polymer that occurs at high frequencies. 23 Composite films were prepared from the stock polymeric solution of PEO in methanol. The polymeric solution was prepared by mixing 0.5 g of PEO powder with 5 ml methanol at 45 C using continuous magnetic stirring for 5 h. Likewise, the stock solution of K 2 PtCl 6 in methanol was prepared by mixing 10 mg of K 2 PtCl 6 powder in 5 ml methanol at nominal room temperature (19-21 C) using continuous magnetic string and ultrasonic repeatedly for around 1 h. The evaporated methanol was substituted to keep the final volume fractions invariant in both stock solutions.…”

“…Additionally, this study aims to investigate if the α ‐relaxation is linked to the local segmental motions of amorphous parts of the main chain of PEO/K 2 PtCl 6 polymer composite. Furthermore, the β ‐relaxation process has to be explored in the meaning of a cooperative segmental motion in the noncrystalline part or the “interphase” between the crystalline and the amorphous segments of the PEO/K 2 PtCl 6 polymer that occurs at high frequencies 23,24 …”