Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)-based hydrogels have emerged as ideal interfacing materials for bioelectronics because of their intriguing electrical, mechanical, and biological properties. However, the development of high-performance PEDOT:PSS-based hydrogels simultaneously achieving high conductivity, robust mechanical properties, and accessibility for advanced manufacturing technologies remains a critical challenge for further advancing such materials toward practical applications. Herein, we develop a highly conductive, intrinsically soft, tough yet stretchable PEDOT:PSS-based hydrogel via a simple PSS-chain engineering strategy of introducing thermally cross-linkable N-(hydroxymethyl)acrylamide segments. The resultant PEDOT:PSS hydrogel exhibits high electrical conductivity (1850 S m–1), high stretchability (>50%), low Young’s modulus (4 MPa), and superior toughness (400 kJ m–3), satisfying multiple property requirements for practical bioelectronic applications. Based on this material, we further develop a novel PEDOT:PSS ink with superior 3D printability for direct ink writing 3D printing, enabling us to facilely fabricate bioelectronic devices like soft skin electrodes comparable to commercial products via multi-material 3D printing.
Conjugated polymers featuring thermally activated delayed fluorescence (TADF) attract tremendous attention in both academic and industry communities due to their easy solution processing for fabricating large-area and low-cost high-performance polymer light-emitting diodes (PLEDs). However, current nondoped solution-processed PLEDs frequently encounter significant efficiency roll-offs and unreasonably high operating voltages at high brightness, especially for red-emitting polymers. Herein, we design hyperbranched conjugated polymers (HCPs) with D−A−D type TADF characteristics for high-performance red-emitting PLEDs. Multiple intramolecular charge transfer (ICT) channels induced by quasi-equivalent donors of the TADF core strongly boost the reverse intersystem crossing (RISC) process and singlet excitons radiative transition. Coupling with the efficient energy transfer process generated by structure advantages of HCPs, the strongly electron-withdrawing oxygen atoms located on the TADF cores further accelerate hole transportation from the host chains to the TADF cores. Under a rational regulation of the TADF core ratio, the related nondoped red-emitting device performs an outstanding performance with an EQE max of 8.39% and exhibits no roll-off while the luminance is less than 100 cd/m 2 and only 3.3% decrease at 500 cd/m 2 . Simultaneously, the EQE can maintain 7.4% under 1000 cd/m 2 . Furthermore, the corresponding nondoped device exhibits a low turn-on voltage of around 2.5 V and achieves a luminance of 500 cd/m 2 at 3.5 V and even 1000 cd/m 2 at 3.9 V. To our knowledge, this is the best performance among all nondoped red PLEDs with high brightness obtained at low operating voltage.
The blends of high and low molecular weights poly(ε-caprolactone) (PCL) with poly(vinyl chloride (PVC) were prepared. The samples before and after the crystallization of PCL were uniaxially stretched to different draw ratios. The orientation features of PCL in a stretched crystalline PCL/PVC blend and crystallized from the amorphous PCL/PVC blends under varied strains were studied by wide-angle X-ray diffraction (WAXD). It was found that a uniaxial stretching of crystalline PCL/PVC blend with high molecular weight PCL results in the c-axis orientation along the stretching direction, as is usually done for the PCL bulk sample. For the stretched amorphous PCL/PVC blend samples, the crystallization of high molecular weight PCL in the blends under a draw ratio of λ = 3 with a strain rate of 6 mm/min leads to a ring-fiber orientation. In the samples with draw ratios of λ = 4 and 5, the uniaxial orientation of a-, b-, and c-axes along the strain direction coexist after crystallization of high molecular weight PCL. With a draw ratio of λ = 6, mainly the b-axis orientation of high molecular weight PCL is identified. For the low molecular weight PCL, on the contrary, the ring-fiber and a-axis orientations coexist under a draw ratio of λ = 3. The a-axis orientation decreases with the increase of draw ratio. When the λ reaches 5, only a poorly oriented ring-fiber pattern has been recognized. These results are different from the similar samples stretched at a higher strain rate as reported in the literatures and demonstrate the important role of strain rate on the crystallization behavior of PCL in its blend with PVC under strain.
Bent and faceted single crystals of poly(vinylidene fluoride) (PVDF) were prepared by isothermal crystallization in its blends with poly(butylene succinate) (PBS). After removing PBS by CHCl 3 washing, the remaining PVDF crystals were examined by optical, atomic force, and transmission electron microscopies and Fourier transform infrared spectroscopy. PVDF single crystals are attributed to α-phase and can reach hundreds of microns with two or more bent branches. The C-and X-shaped crystals are composed of bent basal lamellae, seen flat-on, with a great number of overgrowths. The overgrowths are lozenge-shaped, small-sized single crystals, and most of them grow along the C curves of either C-shaped or X-shaped crystals, keeping the same growth direction with the basal one. Consequently, the electron diffraction patterns taken everywhere of the whole crystal exhibit always a single crystal feature but change constantly with b-axis. These may be attributed to the unbalanced growth of four (110) faces and an inhomogeneous surface order or arrangement of loops and cilia. The lozenge-shaped, large-sized monolayer crystal can be observed upon decreasing the film thickness but without overgrowth, and its shape changes with crystallization temperature. These results can help to understand the surface structure of lamellae and its proliferation process profoundly.
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