Multi-region to single region shear thinning transitions in drying PEDOT:PSS dispersions: contributions from charge density fluctuations

Abstract

The multiple shear thinning behaviour observed in dispersions of the conducting polymer, poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS), in water during the drying process is explored. PEDOT:PSS dispersions in water can be non-stoichiometric polyelectrolyte complexes (PECs) with free polyanion (PSS) chains resulting in scrambled egg conformations. They also behave as charged colloidal particles. The behaviour of PEDOT:PSS dispersions as PECs and charged colloidal systems during drying is analyzed using rheology and TEM, zeta potential, conductivity, pH, dynamic light scattering (DLS) and rheo-small angle light scattering (rheo-SALS) information. The rheological behaviour is found to have significant contributions from conformational changes in the PEDOT:PSS PEC due to charge density fluctuations affecting the electrostatic persistence length, l_e. A low concentration regime with multiple shear thinning behaviour and a high concentration regime with single shear thinning behaviour were observed. The PEC behavior of PEDOT:PSS is further explored by charge neutralizing the dispersions with salts.