CHARGE EFFECT OF THE CATION ON THE STRUCTURE AND THE MOLECULAR MOBILITY OF POLYMER ELECTROLYTES

A study of the thermal and mechanical characteristics of polyethylene oxide-Fe(SCN)3 complexes shows the existence of structures which can b e described by considering a crystalline phase of pure polyethylene ox ide (PEO) and an amorphous phase of PEO with dissolved salt. Increasin g salt contents decrease the content of crystals, favoring the formati on of complexes with a high degree of noncrystallinity as a result of strong polymer-salt interactions which tend to enhance the distortion degree of the polymeric skeleton. The microscopic homogeneity of the c omplexes is also confirmed by the presence in the thermal and mechanic al spectra of single glass transitions, which shift to higher temperat ures with increasing salt content. Two molecular relaxations are prese nt in the mechanical behavior of these systems, the gamma- and the alp ha(a)-processes at low and high temperatures, respectively, and show a relaxation strength which increases with decreasing degree of crystal linity of the polymer up to a X approximately 0.10 molar fraction. Bot h relaxations exhibit a marked nonexponentiality which has been well a ccounted for in terms of a gaussian distribution of relaxation times f or the gamma-process and of the Kolrausch-Williams-Watt exponential fu nction for the alpha(a)-process. In the glassy region, the elastic mod ulus E' reveals a linear temperature dependence which has been interpr eted as arising from the anharmonicity of the anharmonicity parameter, which has been ascribed to the influence of the ''free volume'' in de termining the thermal expansivity (C) 1995 John Wiley & Sons, Inc.