| 1. |
- Hultmark, Sandra, 1994, et al.
(författare)
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Impact of oxidation-induced ordering on the electrical and mechanical properties of a polythiophene co-processed with bistriflimidic acid
- 2022
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Ingår i: Journal of Materials Chemistry C. - : Royal Society of Chemistry (RSC). - 2050-7526 .- 2050-7534. ; 11:24, s. 8091-8099
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Tidskriftsartikel (refereegranskat)abstract
- The interplay between the nanostructure of a doped polythiophene with oligoether side chains and its electrical as well as mechanical properties is investigated. The degree of order of the polymer is found to strongly vary when co-processed with bistriflimidic acid (H-TFSI). The neat polythiophene as well as strongly oxidized material are largely disordered while intermediate concentrations of H-TFSI give rise to a high degree of π-stacking. The structural disorder of strongly oxidized material correlates with a decrease in the kinetic fragility with H-TFSI concentration, suggesting that positive interactions between TFSI anions and the polymer reduce the ability to crystallize. The electrical conductivity as well as the Young's modulus first increase upon the addition of 4-10 mol% of H-TFSI, while the loss of π-stacking observed for strongly oxidized material more significantly affects the latter. As a result, material comprising 25 mol% H-TFSI displays an electrical conductivity of 58 S cm−1 but features a relatively low Young's modulus of only 80 MPa. Decoupling of the electrical and mechanical properties of doped conjugated polymers may allow the design of soft conductors that are in high demand for wearable electronics and bioelectronics.
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| 2. |
- Kim, Donghyun, 1986-
(författare)
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Computational study of Polymerization, Crystallization and Mechanical Properties of Conducting Polymers
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nowadays, electronic devices that include conducting polymers, ranging from batteries and OLED panel for TVs and smartphones to bioelectronics devices such as sensors and ion-pumps for drug-delivery are widely used in our life. The use of conducting polymer in many electronic applications was driven by demand for light weight, flexibility or biocompatibility with the performance on pair with conventional inorganic counterparts. As a result, during last two decades conducting polymers have been a subject of significant interest in both academia and industry. Though many aspects of conducting polymers’ nature have been disclosed, it is still challenging to design a conducting polymer that meets required electrical and mechanical properties. It is because these properties are simultaneously influenced by many various factors such as charge carrier concentration, molecular weight, chemical structure. Thus, understanding the polymerization, crystallization and morphology of conducting polymers is a crucial key to realize flexible, stretchable or wearable electric applications based on conducting polymers. Computational methods represent an important tool in studies of conducting polymer since they not only provide information about morphology of polymer films on molecular level, but also can describe physical properties such as thermodynamic potential and pair-wise interaction between chains that experimental studies can rely on. This thesis is focused on two classes of conducting polymers: Thiophene-based polymers (PEDOT and p(g42T-T)) and NDI-based polymers (pNDI-TVT-TET). The former is one of the most versatile p-type materials, while the latter is known to have ambipolar charge transport owing to its donor-acceptor structure. First, we corroborated the mechanism of in-situ chemical polymerization of PEDOT with Fe(TOS)3 as oxidant by reaction energy calculation for the conventional oxidation polymerization mechanism. We found that doping of PEDOT chain became energetically unfavorable beyond of 33% doping level and we explained it in terms of polaron localization. To explore the impact of polymerization temperature on PEDOT length, we developed a polymerization model for in-situ chemical polymerization of PEDOT:TOS. The results demonstrate that the average PEDOT length is 6, 7, and 11 monomer units at 298, 323, and 373K respectively, and we concluded that the diffusivity of reactants was a dominant factor determining the PEDOT length. We also investigated the effect of molecular doping on the morphology of p(g42T-T) films and their mechanical properties. Doping of p(g42T-T) by TFSI from 0% to 10% gradually increases the - stacking between polymers. It is also found that when doped by F4TCNQ, the elastic modulus and electrical conductivity of films increases until the doping level of about 18%. We attribute these results to the increasing of -stacking between inter-polymer backbones upon increasing the doping levels from 0% to 18%. Finally, the impact of the ratio of TVT/TET in pNDI-TVTx-TET1-x on the morphology and mechanical properties was studied. From MD simulations, we find that the π-π stacking between polymers as the TVT content increases till 50% and afterwards slightly decreases. In addition, a thin-film transistor with the TVT content of 60 or 80% shows a better conductivity than the one with 100% content when it is bent. Our findings on polymerization of conducting polymers, evolution of crystalline and mechanical properties provide theoretical insight that can help a practical improvement in the field of flexible organic electric devices.
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| 3. |
- Kim, Donghyun, 1986, et al.
(författare)
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In-Depth Understanding of the Effect of the Distribution of Substituents on the Morphology and Physical Properties of Ethylcellulose: Molecular Dynamics Simulations Insights
- 2024
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Ingår i: Biomacromolecules. - 1525-7797 .- 1526-4602. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- Ethylcellulose (EC) is a crucial cellulose derivative with widespread applications, particularly in the pharmaceutical industry, where precise property adjustments through chemical modification are imperative. The degree of substitution (DS) and the localization of substituents along the cellulose chains are pivotal factors in this process. However, the impact of the substituent location within the repeating unit of EC remains unexplored. To address this gap, we conducted molecular dynamics simulations on amorphous EC, comparing randomly and uniformly substituted ethyl groups in the repeating units. This comprehensive study of pairwise interactions revealed significant differences in intramolecular and intermolecular hydrogen-bonding capabilities, depending on whether the hydroxyl groups were substituted at C2, C3, or C6. While our simulations demonstrated that substituent localization in the repeating unit influenced the density, number of hydrogen bonds, and conformations, the DS emerged as the dominant determinant. This insight led us to propose and validate a hypothesis: a straightforward linear function using the properties of uniform models and molar fractions can predict the properties of randomly substituted EC with a given DS. This innovative approach is anticipated to contribute to the selection of cellulose derivatives with desirable properties for the pharmaceutical industry and new applications in other fields.
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| 4. |
- Zhao, Dan, et al.
(författare)
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Mechanical, Morphological, and Charge Transport Properties of NDI Polymers with Variable Built-in Π-Conjugation Lengths Probed by Simulation and Experiment
- 2024
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Ingår i: Advanced Functional Materials. - : WILEY-V C H VERLAG GMBH. - 1616-3028 .- 1616-301X. ; 34:4
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Tidskriftsartikel (refereegranskat)abstract
- Mechanically deformable polymeric semiconductors are a key material for fabricating flexible organic thin-film transistors (FOTFTs)-the building block of electronic circuits and wearable electronic devices. However, for many pi-conjugated polymers achieving mechanical deformability and efficient charge transport remains challenging. Here the effects of polymer backbone bending stiffness and film microstructure on mechanical flexibility and charge transport are investigated via experimental and computational methods for a series of electron-transporting naphthalene diimide (NDI) polymers having differing extents of pi-conjugation. The results show that replacing increasing amounts of the pi-conjugated comonomer dithienylvinylene (TVT) with the pi-nonconjugated comonomer dithienylethane (TET) in the backbone of the fully pi-conjugated polymeric semiconductor, PNDI-TVT100 (yielding polymeric series PNDI-TVTx, 100 >= x >= 0), lowers backbone rigidity, degree of texturing, and pi-pi stacking interactions between NDI moieties. Importantly, this comonomer substitution increases the mechanical robustness of PNDI-TVTx while retaining efficient charge transport. Thus, reducing the TVT content of PNDI-TVTx suppresses film crack formation and dramatically stabilizes the field-effect electron mobility upon bending (e.g., 2 mm over 2000 bending cycles). This work provides a route to tune pi-pi stacking in pi-conjugated polymers while simultaneously promoting mechanical flexibility and retaining good carrier mobility in FOTFTs.
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