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Published on: February 23, 2017
Time-pH and time-humidity scaling of ionic conductivity spectra of polyelectrolyte multilayers
Jannis Schlicke1,2, Cornelia Cramer1,2, Monika Schönhoff1,2
1Institute of Physical Chemistry, University of Münster, Corrensstraße 28/30, 48149 Münster, Germany. schoenho@uni-muenster.de.
Abstract:
In this systematic study, ionic conductivity spectra of poly(diallyl-dimethylammonium)/poly(acrylic acid) (PDADMA/PAA) polyelectrolyte multilayers (PEMs) are investigated regarding superposition principles. In this context, charge transport as well as charge compensation processes in polyelectrolyte assemblies are discussed. The validity of different scaling concepts is tested to differentiate between changes in the mobility and charge carrier density, caused by the variation of a parameter X, where X is either relative humidity during measurement, or salt concentration or pH during preparation. For the first time, time-X scaling for conductivity spectra of PEMs is reported for all three parameters X, resulting in individual mastercurves. Furthermore, a super-mastercurve can be obtained including variations of all three parameters. Changes in plasticization caused by either varied humidity, pH or ionic strength imply non-constant charge carrier mobilities in accordance with a Summerfield-type of scaling, while the charge carrier density remains constant. Interestingly, for preparation conditions which favor extrinsic charge compensation, significant deviations from such Summerfield-type scaling are observed, indicating a variation of the number density of mobile charge carriers with humidity.
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