(325g) Understanding PSS:PEDOT Conductivity Enhancement through Thermodynamic Solution Theory

To systematically understand the interactions among PSS, PEDOT and additives, linear solvation energy relationship (LSER) A and B descriptors, the hydrogen bond acidity and basicity, of PSS and PEDOT monomers and additives were obtained. PSS:PEDOT and its conductivity enhancement additives may be categorized into two groups, B only and A+B. PEDOT is B only type so does DMSO. PSS is A+B type, so does EG. The Gibbs free energy of varies hydrogen bonding were calculated using predictive molecular thermodynamic model [Panayiotou et al., Polymer 136:47-61 (2018)].

From previous study, PSS polymer chain is much more flexible than PEDOT polymer chain. Therefore, PSS monomer hydrogen bond to PEDOT forming PSS:PEDOT maybe view as a solvation process. Meanwhile, portion of PSS monomer will hydrogen bond to its neighboring PSS monomer from its own chain or even neighboring chain, together with π-π staking, forming PSS:PSS. The self-hydrogen bonded PSS:PSS does not interact with PEDOT, equivalent to inert solvent, creating entropy driven system that can be described by AO model [J. Polym. Sci. 33, 183 (1958)]. AO model predicts an attractive force between the particles, PEDOT, suspended in solution of macromolecules, forming PEDOT aggregates that leads to pristine conductivity. Inert solvents act similar to self-hydrogen bonded PSS:PSS create very little conductivity enhancement effect.

B only solvent additives interacts not but competes with PEDOT to form hydrogen bond with PSS reduces excess PSS:PEDOT pair allowing PEDOT to form ordered aggregates, phase change from isotropic to ordered state can be found in DSC results. A+B solvent additives not only interact with PSS but also PEDOT creating the screen effect on PEDOT, with the concentration of solvent increases, self-screening themselves may occur which results in saturation in the screening effect.