ACS_Applied Materials & Interface


ACS_Applied Materials & Interface

January 18, 2023

Volume 15, Issue 2

Pages 2499-3688

Protic Ionic Liquids for Intrinsically Stretchable Conductive Polymers

Inspired by the classic hard–soft acid–base theory and intrigued by a theoretical prediction of spontaneous ion exchange between poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and hard-cation–soft-anion ionic liquid (IL), we treat PEDOT:PSS with a new IL composed of a protic (i.e., extremely hard) cation (3-methylimidazolium, p-MIM+) and an extremely soft anion (tetracyanoborate, TCB–). In fact, this protic IL (p-MIM:TCB) accomplishes the same levels of ion-exchange-mediated PEDOT–PSS separation, PEDOT-rich nanofibril formation, and electrical conductivity enhancement (∼2500 S/cm) as its aprotic counterpart (EMIM:TCB with 1-ethyl-3-methylimidazolium), the best IL used for this purpose so far. Furthermore, p-MIM:TCB significantly outperforms EMIM:TCB in terms of improving the stretchability (i.e., the highest tensile strain) of the PEDOT:PSS thin film. This enhancement is a result of the aromatic and protic cation p-MIM+, which acts as a molecular adhesive holding the exchanged ion pairs (PEDOT+:TCB–---p-MIM+:PSS–) via ionic intercalation (at the surface of TCB–-decorated PEDOT+ clusters) and hydrogen bonding (to PSS–), in which washing p-MIM+ out of the film degrades the stretchability while keeping the morphology. Our results offer molecular-level insight into the morphological, electrical, and mechanical properties of PEDOT:PSS and a molecular-interaction-based enhancement strategy that can be used for intrinsically stretchable conductive polymers.

  • Minji Kim
  • Seung Yeob Lee
  • Jihyun Kim
  • Changwon Choi
  • Yves Lansac
  • Hyungju Ahn
  • Sohee Park
  • Yun Hee Jang
  • Seoung Ho Lee
  • Byoung Hoon Lee

Protic Ionic Liquids for Intrinsically Stretchable Conductive Polymers | ACS Applied Materials & Interfaces

Image created by minjeong Kim / Nanosphere