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SYPE: Symposium Polyelectrolytes

SYPE 3: Polyelectrolytes II

SYPE 3.3: Talk

Friday, March 30, 2007, 11:15–11:30, H1

A new method to determine ionic mobilities in polymer electrolytes at low charge carrier density — •Peter Kohn, Klaus Schöter, and Thomas Thurn-Albrecht — Department of Physics, Martin Luther University Halle-Wittenberg, Germany

Apart from mechanical properties the conductivity and its dependence on various parameters like temperature, number of charge carriers, etc., is the decisive quantity for applications of ionically conducting materials. As for other conducting systems the conductivity is determined by the product of the mobility and the number density of the free charge carriers. A basic understanding therefore requires the knowledge of at least one of these quantities in addition to the conductivity.

We present an electrical method that allows an independent determination of the charge carrier density and the mobility of the ions in polymer electrolytes with low density of charge carriers. The number density of free ions is obtained by polarization experiments with high DC-voltages and the ion-mobility can be determined from the transient current after a subsequent voltage reversal.

For an exemplary application we studied polymethylmethacrylate (PMMA) doped with small amounts of a lithium salt (LiCF₃SO₃). A comparison of the values obtained for the ion mobility and the charge carrier density with the conductivity shows good agreement for all salt concentrations studied.