Ionic Liquid for PEDOT:PSS Treatment. Ion Binding Free Energy in Water Revealing the Importance of Anion Hydrophobicity

Water solubility of PEDOT:PSS conducting polymer s achieved by PSS at the expense of disturbing the crystallinity and lectron mobility of PEDOT. Recently, PEDOT crystallinity and lectron mobility have been improved by treating the PEDOT:PSS queous solution with 1-ethyl-3-methylimidazolium-(EMIM-) ased ionic liquids (IL) EMIM:X. The amount of such improvement aries drastically with the anion X coupled to EMIM cation in he IL. Herein, using umbrella-sampling molecular dynamics imulations on the aqueous solutions of a minimal model of EDOT:PSS mixed with various EMIM:X ILs, we show that the olvation of each ion in water plays a major role in the free energies f ion binding and exchange. Anions X efficient for the mprovement are weakly stabilized by hydration (i.e., hydrophobic) and prefer binding to hydrophobic PEDOT than to hydrophilic MIM, favoring the ion exchange. In order to fulfill our design principle, a quantitative criterion based on hydration free energy is roposed to select efficient hydrophobic anions X.