Abstract
Conducting polymers operating in aqueous electrolyte represent mixed electron-ion conductors, where the ion injection and water intake can lead to structural and morphological changes that can strongly affect the material morphology and device performance. In the present paper, using molecular dynamics simulations, we provide an atomistic understanding of the structural phase transitions during electrochemical oxidation and ion injection in a conjugated polymer with glycolated side chains recently reported by Bischak et al. [J. Am. Chem. Soc., 2020, 142, 7434], where the polymer switched between two structurally distinct phases corresponding to different oxidation levels. To outline the structural changes, we calculated the polymer film morphology and X-ray diffraction patterns at different oxidation levels. We demonstrated that the observed phase transition arises due to interplay between several factors, including the effect of the substrate leading to the preferential edge-on arrangement of the chains and formation of lamellas; unzipping of the interdigitated polymer chains during oxidation and ion intake; and changes in the morphology when π–π stacking is absent at low oxidation level and forms at the high oxidation level facilitating the electron mobility and enabling the oxidation of the polymer film. Our calculations quantitatively reproduce the experimental data, which outlines the predictive power of the molecular modeling of the polymer systems that can be utilized for the design of materials and devices with improved performance.
Highlights
Conducting polymers operating in an aqueous electrolyte represent mixed electron-ion conductors, and they are widely utilized in a variety of devices where the coupling between the electronic and ionic motion is the prerequisite for the device functionality.[1]
Devices utilizing a mixed electron-ion conduction such as organic electrochemical transistors (OECT),[5] neural probes,[6] and ion pumps[7] are the cornerstone of the organic bioelectronics as they provide the interface between the biological systems and conventional electronics relying on electron signals
In the present paper, using molecular dynamics simulations, we provide an atomistic understanding of reversible structural phase transitions during electrochemical oxidation and ion injection recently reported by Bischak et al.[19] in a conjugated polymer with glycolated side chains [2,5-bis(thiophenyl)-1,4bis(2-(2-(2-methoxyethoxy)ethoxy)-ethoxy)benzene] (PB2TTEG), where the polymer switched between two structurally distinct crystalline phases corresponding to different oxidation levels
Summary
Conducting polymers operating in an aqueous electrolyte represent mixed electron-ion conductors, and they are widely utilized in a variety of devices where the coupling between the electronic and ionic motion is the prerequisite for the device functionality.[1]. Careful engineering of the side chains of conjugated polymers resulted in improved control of ion injection and water intake, leading to boosting the stability and performance of OECTs.[17,21] Ion injection led to a significant volume expansion ranging from 1000 to 10 000%13 and to reversible structural phase transitions during cyclic voltammetry.[19] While a significant amount of empirical knowledge is gained from the accumulated experimental results, in many cases, the underlying physical and electrochemical processes affecting and Received: September 22, 2020 Accepted: December 2, 2020 Published: December 11, 2020. It is important to stress that the calculated X-ray diffraction curves are in qualitative agreement and in quantitative agreement with the reported experimental data This outlines the predictive power of computational microscopy of polymer systems that can be utilized for the design of materials and devices with improved performance
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