More Like this

1. Mechanical, Morphological, and Charge Transport Properties of NDI Polymers with Variable Built‐in Π‐Conjugation Lengths Probed by Simulation and Experiment

   https://doi.org/10.1002/adfm.202310071  

   Zhao, Dan; Kim, Donghyun; Ghosh, Sarbani; Wang, Gang; Huang, Wei; Zhu, Zonglong; Marks, Tobin J.; Zozoulenko, Igor; Facchetti, Antonio (October 2023, Advanced Functional Materials)

   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 π‐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 π‐conjugation. The results show that replacing increasing amounts of the π‐conjugated comonomer dithienylvinylene (TVT) with the π‐nonconjugated comonomer dithienylethane (TET) in the backbone of the fully π‐conjugated polymeric semiconductor, PNDI‐TVT₁₀₀(yielding polymeric series PNDI‐TVT_x, 100 ≥x≥ 0), lowers backbone rigidity, degree of texturing, and π–π stacking interactions between NDI moieties. Importantly, this comonomer substitution increases the mechanical robustness of PNDI‐TVT_xwhile retaining efficient charge transport. Thus, reducing the TVT content of PNDI‐TVT_xsuppresses 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 π–π stacking in π‐conjugated polymers while simultaneously promoting mechanical flexibility and retaining good carrier mobility in FOTFTs. 

   more » « less
2. Characterization of nanoscale morphology and mechanical properties of conjugated polymer thin films dynamically exposed to a secondary solvent

   https://doi.org/10.1016/j.polymer.2023.126625  

   House, Krystal L; Christian, Kent H; Emge, Thomas J; Pacheco, Haydee; Haber, Richard A; O'Carroll, Deirdre M (February 2024, Polymer)

   Solution processing techniques are often used to enhance intra and interchain order in semiconducting conjugated polymer thin films used in the active layer of organic optoelectronic devices. We investigate the nanomechanical properties of conjugated polymer thin films arising from solution processing techniques. We find that Young’s Modulus data measured by AM-FM AFM can detect additional changes in film properties not discernible by other commonly used bulk thin-film characterization techniques. For PBDB-T-SF, we detect an increase in molecular order that is not noticable by UV–visible absorption spectroscopy, X-ray diffraction or nanoindentation. PCDTBT, the most amorphous of the polymers studied, shows no changes in absorption or X-ray diffraction data, yet clear changes in Young’s Modulus were detected by AFM. Our study demonstrates the applicability of nanomechanical measurements for characterizing local structural variations in conjugated polymer films. This work is relevant to ongoing efforts to control and understand the complex structure-property-processing relationships of conjugated polymer thin films. 

   more » « less
3. Highly Deformable Rigid Glassy Conjugated Polymeric Thin Films

   https://doi.org/10.1002/adfm.202306576  

   Wang, Yunfei; Zhang, Song; Freychet, Guillaume; Li, Zhaofan; Chen, Kai‐Lin; Liu, Chih‐Ting; Cao, Zhiqiang; Chiu, Yu‐Cheng; Xia, Wenjie; Gu, Xiaodan (December 2023, Advanced Functional Materials)

   Abstract Wearable devices benefit from the use of stretchable conjugated polymers (CPs). Traditionally, the design of stretchable CPs is based on the assumption that a low elastic modulus (E) is crucial for achieving high stretchability. However, this research, which analyzes the mechanical properties of 65 CP thin films, challenges this notion. It is discovered that softness alone does not determine stretchability; rather, it is the degree of entanglement that is critical. This means that rigid CPs can also exhibit high stretchability, contradicting conventional wisdom. To inverstigate further, the mechanical behavior, electrical properties, and deformation mechanism of two model CPs: a glassy poly(3‐butylthiophene‐2,5‐diyl) (P3BT) with anEof 2.2 GPa and a viscoelastic poly(3‐octylthiophene‐2,5‐diyl) (P3OT) with anEof 86 MPa, are studied. Ex situ transmission X‐ray scattering and polarized UV–vis spectroscopy revealed that only the initial strain (i.e., <20%) exhibits different chain alignment mechanisms between two polymers, while both rigid and soft P3ATs showed similarly behavior at larger strains. By challenging the conventional design metric of lowEfor high stretchability and highlighting the importance of entanglement, it is hoped to broaden the range of CPs available for use in wearable devices. 

   more » « less
4. Surface Functionalization of 4D Printed Substrates Using Polymeric and Metallic Wrinkles

   https://doi.org/10.3390/polym15092117  

   Agyapong, Johnson N.; Van Durme, Bo; Van Vlierberghe, Sandra; Henderson, James H. (May 2023, Polymers)

   Wrinkle topographies have been studied as simple, versatile, and in some cases biomimetic surface functionalization strategies. To fabricate surface wrinkles, one material phenomenon employed is the mechanical-instability-driven wrinkling of thin films, which occurs when a deforming substrate produces sufficient compressive strain to buckle a surface thin film. Although thin-film wrinkling has been studied on shape-changing functional materials, including shape-memory polymers (SMPs), work to date has been primarily limited to simple geometries, such as flat, uniaxially-contracting substrates. Thus, there is a need for a strategy that would allow deformation of complex substrates or 3D parts to generate wrinkles on surfaces throughout that complex substrate or part. Here, 4D printing of SMPs is combined with polymeric and metallic thin films to develop and study an approach for fiber-level topographic functionalization suitable for use in printing of arbitrarily complex shape-changing substrates or parts. The effect of nozzle temperature, substrate architecture, and film thickness on wrinkles has been characterized, as well as wrinkle topography on nuclear alignment using scanning electron microscopy, atomic force microscopy, and fluorescent imaging. As nozzle temperature increased, wrinkle wavelength increased while strain trapping and nuclear alignment decreased. Moreover, with increasing film thickness, the wavelength increased as well. 

   more » « less
5. An indacenodithiophene-based semiconducting polymer with high ductility for stretchable organic electronics

   https://doi.org/10.1039/C7PY00435D  

   Li, Yilin; Tatum, Wesley K.; Onorato, Jonathan W.; Barajas, Sierra D.; Yang, Yun Young; Luscombe, Christine K. (January 2017, Polymer Chemistry)

   An alkyl-substituted indacenodithiophene-based donor–acceptor π-conjugated polymer ( PIDTBPD ) with low stiffness and high ductility is reported. The polymer was synthesized after DFT calculations predicted that it would have a kinked backbone conformation while showing strong intramolecular charge transfer (ICT), suggestive of the fact that it would be beneficial to the polymer's elasticity and charge mobility. Atom-efficient direct arylation polymerization (DArP) was exploited to synthesize the polymer. Mechanical studies indicate that PIDTBPD has relatively rapid stress-relaxation properties, which lead to a low elastic modulus of 200 MPa and high crack-onset strain of ca . 40% (lower limit). A moderate charge carrier mobility of 2 × 10 −3 cm 2 V −1 s −1 with a current on/off ratio of 2.5 × 10 6 was obtained from the fabricated OFETs. Further experiments were performed to elucidate the structural aspects of this polymer: UV-Vis and PL spectra suggest that minimal conformational change occurs in the polymer between its diluted solution and thin film states; DSC measurements indicate that the polymer's T g is below −20 °C, allowing it to be in a rubbery state at room temperature; and XRD studies support this observation suggesting that the polymer is mostly amorphous at room temperature. 

   more » « less