Effect of pH on ion dynamics in composite PPy/heparin films

Novel composite polypyrrole/heparin films with cation-exchange properties were synthesized by the electrochemical polymerization of pyrrole in the presence of heparin acting as a dopant anion at neutral pH. Heparin was found to be permanently entrapped in the polypyrrole membrane which resulted, as expected, in the mass transport facilitated by mobile cationic counterions. In acidic solutions, polypyrrole/heparin films function as an anion-exchange membrane. Reversible changes from anion dynamics to cation dynamics have been observed upon changes in the solution pH. Information on the polymerization process and characterization of charge transport and mass transport properties in these films were obtained by using the electrochemical quartz crystal microbalance technique (EQCM).