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

Abstract

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

Electronic, Optical, Morphological, Transport, and Electrochemical Properties of PEDOT: A Theoretical Perspective

“…MD simulations addressing various aspects of PEDOT morphology and structure have been recently reported, which includes the PEDOT:PSS interaction with solvent and dopant ions, , the PEDOT:PSS interaction with ionic liquids, , the structure of PEDOT on a steel surface, the wetting behavior of PEDOT:PSS, modeling of interfaces in flexible organic electronic devices, , the calculation of the thermal conductivity, , and others.…”

“…The detailed microscopical origin of this enhancement is still under debate, and we believe that MD calculations are in position to shed line on this issue. The first steps in this direction are reported for the case of ionic liquids for small model systems. , However, further simulation reaching the scale of realistic films and accounting for the PEDOT- and PSS-rich regions are desirable.…”

“…Different modifications of the resulting morphology were obtained depending on the initial structure (homogeneous and granular), which represented relevant experimentally obtained morphologies using different protocols (with 88 and without 86 ultrasonication); see Figure 4c. MD simulations addressing various aspects of PEDOT morphology and structure have been recently reported, which includes the PEDOT:PSS interaction with solvent and dopant ions, 81,89 the PEDOT:PSS interaction with ionic liquids, 82,90 the structure of PEDOT on a steel surface, 91 the wetting behavior of PEDOT:PSS, 92 modeling of interfaces in flexible organic electronic devices, 93,94 the calculation of the thermal conductivity, 95,96 and others.…”

Correlation of Thermoelectric Performance, Domain Morphology and Doping Level in PEDOT:PSS Thin Films Post‐Treated with Ionic Liquids

“…So far, a variety of different ionic liquids were used to improve the PEDOT:PSS properties. Especially, a majority of investigations was focused on different ethyl‐3‐methylimidazolium (EMIM) [ 44,47–49 ] ILs, such as 1‐ethyl‐3‐methylimidazolium tricyanomethanide (EMIM TCM), [ 50–52 ] 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMIM BF 4 ), [ 33 ] or ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI). [ 53 ] For example, Kee et al.…”

Structural modulation induced by cobalt‐based ionic liquids for enhanced thermoelectric transport in PEDOT:PSS

“…The enhanced Seebeck coefficient induced by ionic liquid treatment reportedly results from control of doping level, mostly via a reducing process, [7b,d,e] ascribed to the properties [7f,11] of the anions. From the application point of view, it is important to extend the option of post‐treatment agents beyond expensive and toxic imidazole based ILs or corrosive sulfuric acids.…”