Uniaxial Tensile Deformation of Poly(ε-caprolactone) Studied with SAXS and WAXS Techniques Using Synchrotron Radiation

The structural evolution of poly­(ε-caprolactone) (PCL) during uniaxial tensile deformation at 25 °C was examined using small- and wide-angle X-ray scatterings (SAXS and WAXS) techniques with simultaneous stress and strain (S–S) curves. A high-energy X-ray beam at the recently upgraded Pohang synchrotron radiation source revealed the complete lamellar deformation behavior of PCL. Slope-based division of the S–S curves indicated three distinct regions of elastic (region I), yielding (region II) and plastic deformations (region III). In region I, which showed elastic deformation, the WAXS patterns were isotropic, whereas the SAXS patterns became oblate due to elongation of the amorphous chains along the draw direction. In region II, which showed yielding deformation, the WAXS patterns showed a slight orientation, whereas the SAXS patterns exhibited a change from oblate to four-point and to six-point patterns due to the simultaneous fragmentation and melting of the chain-folded lamellae (leading to the four-point pattern) and the subsequent formation of chain-extended lamellae (adding another two maxima along the meridian). In region III, the WAXS patterns revealed the development of the orientation of PCL crystals, whereas SAXS patterns exhibited a two-point pattern. The newly formed chain-extended lamellae in regions II and III might produce network junctions that can transfer an applied force to the PCL crystals for increased orientation. The six-point pattern in region II for PCL was not observed or reported in the past during the uniaxial tensile deformation experiment. This might be due to fast acquisition of the X-ray patterns during mechanical drawing using synchrotron radiation

Boosting the Ambipolar Performance of Solution-Processable Polymer Semiconductors via Hybrid Side-Chain Engineering

Ambipolar polymer semiconductors are highly suited for use in flexible, printable, and large-area electronics as they exhibit both <i>n</i>-type (electron-transporting) and <i>p</i>-type (hole-transporting) operations within a single layer. This allows for cost-effective fabrication of complementary circuits with high noise immunity and operational stability. Currently, the performance of ambipolar polymer semiconductors lags behind that of their unipolar counterparts. Here, we report on the side-chain engineering of conjugated, alternating electron donor–acceptor (D–A) polymers using diketopyrrolopyrrole-selenophene copolymers with hybrid siloxane-solubilizing groups (<b>PTDPPSe-Si</b>) to enhance ambipolar performance. The alkyl spacer length of the hybrid side chains was systematically tuned to boost ambipolar performance. The optimized three-dimensional (3-D) charge transport of <b>PTDPPSe-Si</b> with pentyl spacers yielded unprecedentedly high hole and electron mobilities of 8.84 and 4.34 cm² V^–1 s^–1, respectively. These results provide guidelines for the molecular design of semiconducting polymers with hybrid side chains

Complex Self-Assembled Morphologies of Thin Films of an Asymmetric A₃B₃C₃ Star Polymer

An asymmetric nine-arm star polymer, (polystyrene)₃-(poly­(4-methoxystyrene))₃-(polyisoprene)₃ (PS₃-PMOS₃-PI₃) was synthesized, and the details of the structures of its thin films were successfully investigated for the first time by using in situ grazing incidence X-ray scattering (GIXS) with a synchrotron radiation source. Our quantitative GIXS analysis showed that thin films of the star polymer molecules have very complex but highly ordered and preferentially in-plane oriented hexagonal (HEX) structures consisting of truncated PS cylinders and PMOS triangular prisms in a PI matrix. This HEX structure undergoes a partial rotational transformation process at temperatures above 190 °C that produces a 30°-rotated HEX structure; this structural isomer forms with a volume fraction of 23% during heating up to 220 °C and persists during subsequent cooling. These interesting and complex self-assembled nanostructures are discussed in terms of phase separation, arm number, volume ratio, and confinement effects

Fluorinated Benzothiadiazole (BT) Groups as a Powerful Unit for High-Performance Electron-Transporting Polymers

Over the past few years, one of the most remarkable advances in the field of polymer solar cells (PSCs) has been the development of fluorinated 2,1,3-benzothiadiazole (BT)-based polymers that lack the solid working principles of previous designs, but boost the power conversion efficiency. To assess a rich data set for the influence of the fluorinated BT units on the charge-transport characteristics in organic field-effect transistors (OFETs), we synthesized two new polymers (<b>PDPP-FBT</b> and <b>PDPP-2FBT</b>) incorporating diketopyrrolopyrrole (DPP) and either single- or double-fluorinated BT and thoroughly investigated them via a range of techniques. Unlike the small differences in the absorption properties of <b>PDPP-FBT</b> and its nonfluorinated analogue (<b>PDPP-BT</b>), the introduction of doubly fluorinated BT into the polymer backbone induces a noticeable change in its optical profiles and energy levels, which results in a slightly wider bandgap and deeper HOMO for <b>PDPP-2FBT</b>, relative to the others. Grazing incidence X-ray diffraction (GIXD) analysis reveals that both fluorinated polymer films have long-range orders along the out-of-plane direction, and π–π stacking in the in-plane direction, implying semicrystalline lamellar structures with edge-on orientations in the solid state. Thanks to the strong intermolecular interactions and highly electron-deficient π-systems driven by the inclusion of F atoms, the polymers exhibit electron mobilities of up to 0.42 and 0.30 cm² V^–1 s^–1 for <b>PDPP-FBT</b> and <b>PDPP-2FBT</b>, respectively, while maintaining hole mobilities higher than 0.1 cm² V^–1 s^–1. Our results highlight that the use of fluorinated BT blocks in the polymers is a promising molecular design strategy for improving electron transporting performance without sacrificing their original hole mobility values

A Thienoisoindigo-Naphthalene Polymer with Ultrahigh Mobility of 14.4 cm²/V·s That Substantially Exceeds Benchmark Values for Amorphous Silicon Semiconductors

By considering the qualitative benefits associated with solution rheology and mechanical properties of polymer semiconductors, it is expected that polymer-based electronic devices will soon enter our daily lives as indispensable elements in a myriad of flexible and ultra low-cost flat panel displays. Despite more than a decade of research focused on designing and synthesizing state-of-the-art polymer semiconductors for improving charge transport characteristics, the current mobility values are still not sufficient for many practical applications. The confident mobility in excess of ∼10 cm²/V·s is the most important requirement for enabling the realization of the aforementioned near-future products. We report on an easily attainable donor–acceptor (D–A) polymer semiconductor: poly­(thienoisoindigo-<i>alt</i>-naphthalene) (PTIIG-Np). An unprecedented mobility of 14.4 cm²/V·s, by using PTIIG-Np with a high-<i>k</i> gate dielectric poly­(vinylidenefluoride-trifluoroethylene) (P­(VDF-TrFE)), is achieved from a simple coating processing, which is of a magnitude that is very difficult to obtain with conventional TFTs by means of molecular engineering. This work, therefore, represents a major step toward truly viable plastic electronics

Ambipolar Semiconducting Polymers with <i>π-</i>Spacer Linked Bis-Benzothiadiazole Blocks as Strong Accepting Units

Recognizing the importance of molecular coplanarity and with the aim of developing new, ideal strong acceptor-building units in semiconducting polymers for high-performance organic electronics, herein we present a simplified single-step synthesis of novel vinylene- and acetylene-linked bis-benzothiadiazole (<b>VBBT</b> and <b>ABBT</b>) monomers with enlarged planarity relative to a conventionally used acceptor, benzothiadiazole (BT). Along these lines, four polymers (<b>PDPP-VBBT</b>, <b>PDPP-ABBT</b>, <b>PIID-VBBT</b>, and <b>PIID-ABBT</b>) incorporating either <b>VBBT</b> or <b>ABBT</b> moieties are synthesized by copolymerizing with centro-symmetric ketopyrrole cores, such as diketopyrrolopyrrole (DPP) and isoindigo (IID), and their electronic, physical, and transistor properties are studied. These polymers show relatively balanced ambipolar transport, and <b>PDPP-VBBT</b> yields hole and electron mobilities as high as 0.32 and 0.13 cm² V^–1 s^–1, respectively. Interestingly, the acetylenic linkages lead to enhanced electron transportation in ketopyrrole-based polymers, showing a decreased threshold voltage and inverting voltage in the transistor and inverter devices, respectively. The IID-based BBT polymers exhibit the inversion of the dominant polarity depending on the type of unsaturated carbon bridge. Owing to their strong electron-accepting ability and their highly π-extended and planar structures, <b>VBBT</b> and <b>ABBT</b> monomers should be extended to the rational design of high-performance polymers in the field of organic electronics

Rhodium and Carbon Sites with Strong d–p Orbital Interaction for Efficient Bifunctional Catalysis

Efficient and stable catalysts are highly desired for the electrochemical conversion of hydrogen, oxygen, and water molecules, processes which are crucial for renewable energy conversion and storage technologies. Herein, we report the development of hollow nitrogenated carbon sphere (HNC) dispersed rhodium (Rh) single atoms (Rh1HNC) as an efficient catalyst for bifunctional catalysis. The Rh1HNC was achieved by anchoring Rh single atoms in the HNC matrix with an Rh–N3C1 configuration, via a combination of in situ polymerization and carbonization approach. Benefiting from the strong metal atom-support interaction (SMASI), the Rh and C atoms can collaborate to achieve robust electrochemical performance toward both the hydrogen evolution and oxygen reduction reactions in acidic media. This work not only provides an active site with favorable SMASI for bifunctional catalysis but also brings a strategy for the design and synthesis of efficient and stable bifunctional catalysts for diverse applications

Tunable Film Morphologies of Brush–Linear Diblock Copolymer Bearing Difluorene Moieties Yield a Variety of Digital Memory Properties

An amphiphilic brush–linear diblock copolymer bearing a rigid difluorene moiety was synthesized, yielding a copolymer with a high thermal stability and excellent processability. The immiscibility of the blocks induced the formation of a variety of nanostructures, depending on the fabrication conditions, which differed significantly from the nanostructures observed among common diblock copolymers in similar composition. Interestingly, the orientations of the nanostructures could be controlled. The nanostructured polymer displayed a variety of tunable morphologies that yielded distinct electrical memory properties when incorporated as the active layer into a digital memory device. The memory devices could be operated under very low power consumption levels and displayed excellent unipolar switching properties

Nanostructure- and Orientation-Controlled Digital Memory Behaviors of Linear-Brush Diblock Copolymers in Nanoscale Thin Films

Linear-brush diblock copolymers bearing carbazole moieties in the brush block were synthesized. Various phase-separated nanostructures were found to develop in nanoscale thin films of the copolymers, depending on the fabrication conditions including selective solvent-annealing. This variety of morphologies and orientations means that these block copolymers exhibit digital memory versatility in their devices. Overall, the relationship between the morphology and digital memory performance of these copolymers has several important features. In particular, the carbazole moieties in the vertical cylinder phase with a radius of 8 nm or less can trap charges and also form local hopping paths for charge transport, which opens the mass production of advanced digital memory devices with ultrahigh memory density. Charges can be transported through the layer when the dielectric linear block phase has a thickness of 10.6 nm; however, charge transport is not possible for a dielectric phase with a thickness of 15.9 nm. All the observed memory behaviors are governed by the trap-limited space-charge-limited conduction mechanism and local hopping path (i.e., filament) formation