How side-chain hydrophilicity modulates morphology and charge transport in mixed conducting polymers

A Khot and BM Savoie, JOURNAL OF POLYMER SCIENCE, 60, 610-620 (2022).

DOI: 10.1002/pol.20210773

Organic mixed ionic-electronic conductors (OMIECs) are a developing class of organic electronic materials distinguished by their dual modes of conduction. The side-chains of OMIEC polymers are responsible for forming a percolating electrolyte phase that mediates doping and ionic conduction. Despite this critical role, design rules for OMIEC side- chains are still nascent and their effects on OMIEC morphology and charge transport have yet to be systematically studied. Here we perform the first dedicated coarse-grained molecular dynamics study of OMIECs where the side-chain identity and distribution are systematically varied using a random copolymer architecture. The simulations recapitulate the nonlinear progression of the morphology from an interfacially gated electrolyte when large fractions of hydrophobic side-chains are incorporated, to an electrolyte swelled morphology after crossing a threshold of approximately 40% polar side-chains. Kinetic Monte Carlo simulations were used to characterize the charge transport behaviors in these systems, revealing two interesting maxima in the mobility at 40% and 100% polar side-chain fractions, respectively. With respect to maximizing the charge mobility and conductivity, these simulations suggest that a uniform hydrophilic side-chain distribution is optimal and that there are few advantages to using mixed side-chains in a random copolymer architecture. These results also suggest several alternative side-chain engineering strategies for optimizing OMIEC performance.

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