Abstract
Solid polymer electrolytes are mixtures of polymer and inorganic salt. There are quite a number of studies dealing with the relationship between electric conductivity and structural relaxation in solid polymer electrolytes. We present a phenomenological approach based on fluctuation-dissipation processes. Phase heterogeneity appears in poly(ethylene oxide) (PEO) of high molecular mass and its blends due to crystallization and accompanying phase segregation. Addition of salt hampers crystallization, causing dynamic heterogeneity of the salt mixtures. Conductivity is bound to amorphous phase; the conductivity mechanism does not depend on content of added salt. One observes dispersion of conductivity relaxation only at low frequency. This is also true for blends with poly(methyl methacrylate) (PMMA). In blends, the dynamics of relaxation depend on glass transition of the system. Glassy PMMA hampers relaxation at room temperature. Relaxation can only be observed when salt content is sufficiently high. As long as blends are in rubbery state at room temperature, they behave PEO-like. Blends turn into glassy state when PMMA is in excess. Decoupling of long-ranging and dielectric short-ranging relaxation can be observed. Conductivity mechanism in PEO, as well as in blends with PMMA were analyzed in terms of complex impedance Z*, complex permittivity, tangent loss spectra and complex conductivity.
Highlights
Poly(ethylene oxide) (PEO) is frequently used as a polymer matrix in polymer-salt mixtures.poly(ethylene oxide) (PEO) exhibits low glass transition temperature and, sufficient chain flexibility at ambient temperature
We will discuss dielectric properties of polymer-salt mixtures at room temperature under
The rate increases with concentration YS for PEO and tends to saturation which is given by solubility limit of salt in the amorphous phase of PEO and corresponding phase in blends
Summary
Poly(ethylene oxide) (PEO) is frequently used as a polymer matrix in polymer-salt mixtures. Experiments have revealed that polymer-salt mixtures comprising PEO do consist of an amorphous network-like phase [5,6,7,8,9], and of crystalline domains. One immediately recognizes that Frenkel’s [10] or Schottky’s [11] mechanisms of charge transport in solid polymer electrolytes do not apply here, because conductivity is bound to amorphous regions This phase is not in thermodynamic equilibrium. Highly flexible PEO chains comprising functional ether groups constitute a solvent with low driving force for solubility of inorganic salts These mixtures exhibit low electric conductivity at ambient temperature, an effect caused by both constituents of the mixture. We discuss the influence of constant salt concentration on dielectric properties of solid polymer electrolytes with PEO and blends with PMMA. The mixture of PEO with the variation of Li-salt [15,16] serves as the reference for these blend system
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