Aflatoxin B1 (AFB1) is a highly toxic mycotoxin produced by aspergillus species under specific conditions as secondary metabolites. In this study, types of PCL (Polycaprolactone) membranes anchored (or not) to g-C3N4/CQDs composites were prepared using electrospinning technology with (or without) the following surface modification treatment to remove AFB1. These membranes and g-C3N4/CQDs composites were characterized by SEM, TEM, UV-vis, XRD, XPS and FTIR to analyze their physical and chemical properties. Among them, the modified PCL-g-C3N4/CQDs electrospun membranes exhibited an excellent ability to degrade AFB1 via synergistic effects of adsorption and photocatalysis, and the degradation rate of 0.5 μg/mL AFB1 solution was observed to be up to 96.88% in 30 min under visible light irradiation. Moreover, the modified PCL-g-C3N4/CQDs electrospun membranes could be removed directly after the reaction process without centrifugal or magnetic separation, and the regeneration was a green approach synchronized with the reaction under visible light avoiding physical or chemical treatment. The mechanism of adsorption by electrostatic attraction and hydrogen bonding interaction was revealed and the mechanism of photodegradation of AFB1 was also proposed based on active species trapping experiments. This study illuminated the highly synergic adsorption and photocatalytic AFB1 removal efficiency without side effects from the modified PCL-g-C3N4/CQDs electrospun membranes, thereby offering a continual and green solution to AFB1 removal in practical application.

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Enhancement of AFB1 Removal Efficiency via Adsorption/Photocatalysis Synergy Using Surface-Modified Electrospun PCL-g-C3N4/CQDs Membranes

The “hot exciton” mechanism based on high‐lying reverse intersystem crossing process has great advantages in achieving high‐performance deep‐blue organic light‐emitting diodes (OLEDs). Nevertheless, how to solve the loss of high‐lying excitons to improve device performance further is a pressing and challenging issue. To break through this shackle, a novel deep‐blue emitter based on “exciton recovery” strategy is successfully design, namely CAT. By combining the transient absorption spectrum, theoretical calculation, magneto‐electroluminescence, and transient‐electroluminescence measurements, the multi‐channeled pathways of excitons utilization via hot exciton and triplet‐triplet annihilation processes is comprehensively demonstrated, and the proportion of singlet excitons by each channel. Finally, a high exciton utilization efficiency is successfully achieved, and the non‐doped OLED based on CAT exhibit an excellent external quantum efficiency of 10.39% with the CIE coordinates of (0.15, 0.087). Furthermore, the sensitized blue fluorescent OLED by CAT as host also achieves excellent performance. More importantly, the operational lifetime of the “multi‐channel” sensitized device is evaluated for the first time, performing the remarkable LT50 (lifetime to 50% of the initial luminance) of 320 h at 540 cd m−2. These results fully reveal the significance of the “exciton recovery” strategy and give new inspiration for exploring high‐performance blue OLEDs.

“Exciton Recovery” Strategy in Hot Exciton Emitter toward High‐Performance Non‐Doped Deep‐Blue and Host‐Sensitized Organic Light‐Emitting Diodes

Biobased hybrid composite design for optimum hardness and wear resistance

The local glass transition temperature Tg of pyrene-labeled polystyrene (PS) chains intermixed with end-tethered PS chains grafted to a neutral silica substrate was measured by fluorescence spectroscopy. To isolate the impact of the grafted chains, the films were capped with bulk neat PS layers eliminating competing effects of the free surface. Results demonstrate that end-grafted chains strongly increase the local Tg of matrix chains by ≈45 K relative to bulk Tg, independent of grafted chain molecular weight from Mn = 8.6 to 212 kg/mol and chemical end-group, over a wide range of grafting densities σ = 0.003 to 0.33 chains/nm2 spanning the mushroom-to-brush transition regime. The tens-of-degree increase in local Tg resulting from immobilization of the chain ends by covalent bonding in this athermal system suggests a mechanism that substantially increases the local activation energy required for cooperative rearrangements.

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End-Tethered Chains Increase the Local Glass Transition Temperature of Matrix Chains by 45 K Next to Solid Substrates Independent of Chain Length.

Single-molecule tracking (SMT) methods have been widely employed to offer a high-resolution characterization of synthetic polymers under ambient conditions and, thus, have advanced our understanding of their unique material properties. SMT is based on the systematic monitoring of the diffusive motions of individual fluorescent dye molecules in the as-prepared polymer thin films or thicker monoliths. Quantitative assessment of the recorded SMT video data involves the systematic analysis of the generated diffusion trajectories of a single molecule using well-established and reported methods. The results have offered a wealth of new information on the structural alignment, orientational order, and long-range continuity of the polymer microdomains; the nanoscale material heterogeneities governed by defects, misalignment, and ill-controlled preparation conditions; as well as the various forms of probe–host interactions on the single-molecule level. In the first part of this Tutorial review, we describe the fundamental principles and instrumentation of SMT, before offering interested readers and potential future SMT users a practical guidance on the selection of fluorescent probe molecules, preparation of suitable samples, and optimization of experimental conditions and imaging parameters. Then, we highlight several representative SMT studies in microphase-separated block copolymers, and semicrystalline and amorphous homopolymers to further emphasize the usefulness of SMT methods for polymer characterization without neglecting some of their shortcomings. This Tutorial review is written with the motivation to attract new researchers to the fast-growing field and assist them in starting their own SMT research of synthetic polymers and other technologically useful soft matter systems.

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Single-molecule tracking of dye diffusion in synthetic polymers: A tutorial review

Since the chemical and thermal stability of organic thin film layers in organic light-emitting diodes (OLEDs) highly influences the operational device lifetime, a rational advanced design of materials and device structures is quite necessary. Here, we report a significant improvement in the device thermal stability and operational lifetime of blue-fluorescent OLEDs by adopting a mixed electron transporting layer (mETL) of 4,7-diphenyl-1,10-phenanthroline (BPhen) and hydroxyquinolinolato-lithium (Liq). Compared to pristine BPhen film, Liq mixing improved thermal and morphological stabilities of the mETL by increasing the glass-transition temperature and inhibiting crystallization of the ETL, which directly leads to better device performances. Compared to the reference device using the pristine BPhen film as an ETL, the device with mETL containing 50% Liq maintains the device characteristics, with respect to the thermal stress up to 110 °C, which is a 60 °C increase in the thermal stability of the blue device by applying mETL. Accordingly, the operational lifetime of the device with mETL containing 50% Liq is substantially extended by 67 times, ensuring that this remarkable device lifetime enhancement is dominantly driven by the improved thermal and morphological stabilities of mETL. 

Improved Thermal Stability and Operational Lifetime of Blue Fluorescent Organic Light-Emitting Diodes by Using a Mixed-Electron Transporting Layer

Polymer networks generally consist of an ensemble of single chains. However, understanding how chain conformation affects the structure and properties of polymer networks remains a challenge for optimizing their functionality. Here, we present the fabrication and comparative study of a polymer network composed of collapsed self-entangled chains (intrachain entangled network) and a standard polymer network in which random-coil chains are entangled with each other (interchain entangled network). For poly(methyl methacrylate) thin films composed of these networks, we coupled solvent vapor swelling and single-molecule tracking techniques to examine the anomalies in the dynamics of a small-molecular probe included in the system. We demonstrate that when compared to the interchain entangled network the intrachain one exhibits a more substantial structural heterogeneity, particularly under highly crowded conditions. This network also exhibits physical compactness, which keeps the heterogeneous network structure frozen over time and impedes network plasticization through solvent uptake by the film.

Impact of Chain Conformation on Structural Heterogeneity in Polymer Network.

Rotational-translational decoupling, in which translational motion is apparently enhanced over rotational motion in violation of Stokes-Einstein (SE) and Debye-Stokes-Einstein (DSE) predictions, has been observed in materials near their glass transition temperatures (Tg). This has been posited to result from ensemble averaging in the context of dynamic heterogeneity. In this work, ensemble and single molecule experiments are performed in parallel on a fluorescent probe in high molecular weight polystyrene near its Tg. Ensemble results show decoupling onset at approximately 1.15Tg, increasing to over three orders of magnitude at Tg. Single molecule measurements also show a high degree of decoupling, with typical molecules at Tg showing translational diffusion coefficients nearly 400 times higher than expected from SE/DSE predictions. At the single molecule level, higher degree of breakdown is associated with particularly mobile molecules and anisotropic trajectories, providing support for anomalous diffusion as a critical driver of rotational-translational decoupling and SE/DSE breakdown. 

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Single molecule demonstration of Debye–Stokes–Einstein breakdown in polystyrene near the glass transition temperature

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Kee Jung Paeng

Papers

Improved Thermal Stability and Operational Lifetime of Blue Fluorescent Organic Light-Emitting Diodes by Using a Mixed-Electron Transporting Layer

Impact of Chain Conformation on Structural Heterogeneity in Polymer Network.

Single molecule demonstration of Debye–Stokes–Einstein breakdown in polystyrene near the glass transition temperature

Single molecule demonstration of Debye–Stokes–Einstein breakdown in polystyrene near the glass transition temperature

Polymer segmental dynamics near the interface of silica particles in the particle/polymer composites.