Understanding Solution State Conformation and Aggregate Structure of Conjugated Polymers via Small Angle X-ray Scattering

Journal Article · Thu May 19 00:00:00 EDT 2022 · Macromolecules

DOI:https://doi.org/10.1021/acs.macromol.1c02449· OSTI ID:1961590

Kwok, Justin J. ^[1]; Park, Kyung Sun ^[1]; Patel, Bijal B. ^[1]; Dilmurat, Rishat ^[2]; Beljonne, David ^[2]; Zuo, Xiaobing ^[3]; Lee, Byeongdu ^[3]; Diao, Ying ^[1]

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1. University of Illinois at Urbana-Champaign, IL (United States)
2. University of Mons (Belguim)
3. Argonne National Laboratory (ANL), Lemont, IL (United States). Advanced Photon Source (APS)

Donor-acceptor (D-A) conjugated polymers are high-performance organic electronic materials that exhibit complex aggregation behavior. Understanding the solution state conformation and aggregation of conjugated polymers is crucial for controlling morphology during thin-film deposition and the subsequent electronic performance. However, a precise multiscale structure of solution state aggregates is lacking. Here, we present an in-depth small-angle X-ray scattering (SAXS) analysis of the solution state structure of an isoindigo-bithiophene-based D-A polymer (PII-2T) in chlorobenzene and decane as our primary system. Modeling the system as a combination of hierarchical fibrillar aggregates mixed with dispersed polymers, we extract information about conformation and multiscale aggregation and also clarify the physical origin of features often observed but unaddressed or misinterpreted in small-angle scattering patterns of conjugated polymers. The persistence length of the D-A polymer extracted from SAXS agrees well with a theoretical model based on the dihedral potentials. Additionally, we show that the broad high q structure factor peak seen in scattering profiles can be attributed to lamellar stacking occurring within the fibril aggregates and that the low q aggregate scattering is strongly influenced by the polymer molecular weight. Overall, the SAXS profiles of D-A polymers in general exhibit a sensitive dependence on the co-existence of fibrillar aggregate and dispersed polymer chain populations. We corroborate our findings from SAXS with electron microscopy of freeze-dried samples for direct imaging of fibrillar aggregates. Finally, we demonstrate the generality of our approach by fitting the scattering profiles of a variety of D-A polymers based on thieno-isoindigo (PTII-2T), diketopyrrolopyrrole (DPP2T-TT, DPP-BTZ, PDPP2FT-C-₁₆), naphthalenediimide (P(NDI2OD-T2)), and a conjugated block copolymer P3HT-b-DPPT-T. The results presented here establish a picture of the D-A polymer solution state structure and provide a general method of interpreting and analyzing their scattering profiles.

• Research Organization: Argonne National Laboratory (ANL), Lemont, IL (United States)
• Sponsoring Organization: Coronavirus CARES Act; European Union’s Horizon 2020; Fonds de la Recherche Scientifiques de Belgique (F.R.S.-FNRS); Marie Sklodowska Curie Grant; National Science Foundation (NSF); Office of Naval Research (ONR); USDOE Office of Science (SC), Workforce Development for Teachers and Scientists (WDTS)
• Grant/Contract Number: AC02-06CH11357; SC0014664
• OSTI ID: 1961590
• Journal Information: Macromolecules, Journal Name: Macromolecules Journal Issue: 11 Vol. 55; ISSN 0024-9297
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
conformation
conjugated polymers