Name: Dr. Souvik De
Diploma / M.Sc degree: Indian Institute of Technology Madras, India
(August 2008)

PhD Project: Temperature and humidity dependent transport characteristics of the polyelectrolyte complexes (PEC)


Homepage: http://www.uni-muenster.de/Chemie.pc/schoenhoff/arbeitsgruppe-s.html

Abstract of Research Project

Recently, polyelectrolyte complexes (PEC) as well as polyelectrolyte multilayers (PEM) have gained attention for a variety of applications such as ultrafiltration membrane sensors, for battery charge separators and for solid polyelectrolyte membrane in fuel cells. These materials are found to be promising due to their interesting phases, transport properties and ease of preparation. For example, polyelectrolytes provide better mechanical stability compared to polymer electrolytes. PEM can be made by layer by layer assembly, i.e. the alternative adsorption of polycations and polyanions. On the other hand PEC are formed by complexation of positively and negatively charged polyelectrolytes due to strong electrostatic interactions. The major advantage of PEC over PEM is that the former can be prepared with any desired polyanion to polycation ratio. The current challenge in this field is to prepare PEC which show high conductivity as well as sufficient mechanical stability at elevated temperature. Conductivity depends on the number density of the mobile ions, their charges and their mobility which in turns depends on several external parameters like relative humidity, temperature, preparation procedure etc.
In general electrical characterization of solids can be done by dc and ac measurement techniques. Though the dc measurement technique is straight forward, it cannot be implemented for polyelectrolytes due to the fact that as a dc field is applied to the electrolyte, the material gets polarized and the ionic conductivity gradually decreases. In view of this, impedance spectroscopy (IS) is a powerful tool for conductivity measurement of disordered condensed phase materials and solid polyelectrolytes.
Humidity and temperature dependent conductivity spectra have already been investigated for of PEM and dried PEC respectively and both the parameter are found to influence the conductivity. In this present project we investigate the
1) The water content of the PEC at different relative humidity by means of DTA measurements.
2) Humidity dependence of the dc conductivity: To investigate whether there is an influence of proton or H₃O⁺ ions in the conduction process.
3) Temperature dependence of the dc conductivity: In order to determine the long range transport properties and the activation enthalpy of the conduction process.
4) As the water content changes at different temperature we are also interested to investigate the effect of temperature on dc conductivity at constant water content.


Publications

S. De, C. Cramer, M. Schönhoff
Humidity dependence of the ionic conductivity of polyelectrolyte complexes
Marcromolecules 44(22) (2011), 8936-8943.

C. Cramer, S. De, M. Schönhoff
Time-Humidity-Superposition Principle in Electrical Conductivity Spectra of Ion-Conducting Polymers
Phys. Rev. Lett. 107 (2011), 028301.


Souvik De
eMail: Souvik De