Styrenic Polymer Nanocomposites Based on an Oligomerically-Modified Clay with High Inorganic Content

Clay was modified with an oligomeric surfactant containing styrene and lauryl acrylate units along with a small amount of vinylbenzyl chloride to permit the formation of an ammonium salt so that this can be attached to a clay. The oligomerically-modified clay contains 50% inorganic clay, and styrenic polymer nanocomposites, including those of polystyrene (PS), high-impact polystyrene (HIPS), styrene–acrylonitrile copolymer (SAN) and acrylonitrile–butadiene–styrene (ABS), were prepared by melt blending. The morphologies of the nanocomposites were evaluated by X-ray diffraction and transmission electron microscopy. Mixed intercalated/delaminated nanocomposites were formed for SAN and ABS while largely immiscible nanocomposites were formed for PS and HIPS. The thermal stability and fire properties were evaluated using thermogravimetric analysis and cone calorimetry, respectively. The plasticization from the oligomeric surfactant was suppressed and the tensile strength and Young\u27s modulus were improved, compared to similar oligomerically-modified clays with higher organic content

Learning to Predict Charges for Criminal Cases with Legal Basis

The charge prediction task is to determine appropriate charges for a given case, which is helpful for legal assistant systems where the user input is fact description. We argue that relevant law articles play an important role in this task, and therefore propose an attention-based neural network method to jointly model the charge prediction task and the relevant article extraction task in a unified framework. The experimental results show that, besides providing legal basis, the relevant articles can also clearly improve the charge prediction results, and our full model can effectively predict appropriate charges for cases with different expression styles.Comment: 10 pages, accepted by EMNLP 201

From Simple to Complex: A Progressive Framework for Document-level Informative Argument Extraction

Document-level Event Argument Extraction (EAE) requires the model to extract arguments of multiple events from a single document. Considering the underlying dependencies between these events, recent efforts leverage the idea of "memory", where the results of already predicted events are cached and can be retrieved to help the prediction of upcoming events. These methods extract events according to their appearance order in the document, however, the event that appears in the first sentence does not mean that it is the easiest to extract. Existing methods might introduce noise to the extraction of upcoming events if they rely on an incorrect prediction of previous events. In order to provide more reliable memory, we propose a simple-to-complex progressive framework for document-level EAE. Specifically, we first calculate the difficulty of each event and then, we conduct the extraction following a simple-to-complex order. In this way, the memory will store the most certain results, and the model could use these reliable sources to help the prediction of more difficult events. Experiments on WikiEvents show that our model outperforms SOTA by 1.4% in F1, indicating the proposed simple-to-complex framework is useful in the EAE task.Comment: Accepted to the Findings of EMNLP 2023 (Long Paper

Using In Situ Single-Particle Imaging to Understand the Role of Structural Distortions during Anion Exchange in Cesium Lead Halide Perovskite Nanocrystals

Colloidal cesium lead halide (CsPbX3, X = Cl, Br, I) perovskite nanocrystals are being investigated as promising materials for light-emitting devices and fluorescence probes due to their strong absorption and emission (1.55 eV – 3.05 eV) of visible light. Anion exchange is a facile, post-synthetic method to tune the bandgap emission of CsPbX3 nanocrystals, covering most of the spectrum of visible light. However, structural heterogeneities in nanocrystals formed during anion exchange will lead to lower photoluminescence quantum yield and a broader range of emission wavelengths. A single batch of nanocrystals will contain a distribution of sizes, shapes, surface structures, and defect concentrations. These variations will lead to heterogenous reactivity during chemical transformations such as anion exchange. To enhance the brightness and color purity of light-emitting devices that incorporate CsPbX3 nanocrystals, the factors that control heterogeneous reactivity need to be understood. In this dissertation, we performed research on anion exchange between CsPbBr3 and CsPbI3 nanocrystals using in situ single-particle fluorescence imaging. This method can probe differences in the reactivity of hundreds of nanocrystals undergoing anion exchange at the same time. As the emission from each nanocrystal shifts to longer wavelengths during anion exchange, they turn on and appear as bright spots during the fluorescence video, which indicates their transformation. By analyzing different single-particle reaction trajectories, we assign a switching time, which is a measure of the time it takes the nanocrystal to complete anion exchange. For the transformation of CsPbBr3 nanocrystals to CsPbI3, the average switching time of individual nanocrystals is longer than the reverse transformation of CsPbI3 nanocrystals to CsPbBr3. To understand the kinetics during anion exchange, we performed experiments using different concentrations of substitutional halide anions. We observed a stronger concentration dependence in the average switching times for the forward reaction of CsPbBr3 nanocrystals to CsPbI3 than in the reverse reaction (i.e., CsPbI3 to CsPbBr3). We developed different models using Monte Carlo simulations to rationalize the experimental results. We attribute the difference in switching times to a more abrupt change in structure for the transformation of CsPbI3 nanocrystals to CsPbBr3, arising from a larger change in the tilting angle of PbX6 octahedra. These results indicate that CsPbI3 nanocrystals synthesized by the hot injection method have a different structure than CsPbI3 nanocrystals synthesized by anion exchange. We also studied the size dependence of anion exchange from CsPbBr3 nanocrystals to CsPbI3 using single-particle imaging. We observed a longer average reaction time and a stronger dependence of the average switching time on the concentration of substitutional halide anions for smaller nanocrystals (\u3c 8 nm), compared to nanocrystals with a larger size (\u3e 8 nm). Comparison to ensemble fluorescence spectroscopy indicates we are probing a critical stage of the reaction after anion exchange has initiated on the surface of the nanocrystals. We developed different kinetic models using Monte Carlo simulations to understand this size-dependent reactivity. We attribute the size dependence to a larger structural reorganization that must occur in larger nanocrystals during anion exchange, which leads to a more abrupt transformation compared with smaller nanocrystals. Our results indicate that size-dependent miscibility between CsPbBr3 and CsPbI3 at the nanoscale controls the reaction kinetics. Smaller nanocrystals maintain a homogenous structure during the entire transformation. As the nanocrystal size increases, variations in the tilting patterns of PbX6 octahedra in the perovskite crystals lead to different structures for CsPbBr3 and CsPbI3. Thus, a new iodide-rich phase must first nucleate within larger CsPbBr3 nanocrystals, which is then followed by their rapid transformation. Cumulatively, these results indicate that there are intrinsic variations in the reactivity of nanocrystals undergoing the same transformation. This heterogeneity imposes a limit on the narrowness of emission wavelengths for CsPbX3 nanocrystals prepared by anion exchange. Synthetic methods that maintain a high and uniform concentration of substitutional halide anions during anion exchange will minimize variations in the composition and will maximize the color purity of the resulting CsPbX3 nanocrystals for applications in light-emitting devices

Recent advances in electronic and optoelectronic Devices Based on Two-Dimensional Transition Metal Dichalcogenides

Two-dimensional transition metal dichalcogenides (2D TMDCs) offer several attractive features for use in next-generation electronic and optoelectronic devices. Device applications of TMDCs have gained much research interest, and significant advancement has been recorded. In this review, the overall research advancement in electronic and optoelectronic devices based on TMDCs are summarized and discussed. In particular, we focus on evaluating field effect transistors (FETs), photovoltaic cells, light-emitting diodes (LEDs), photodetectors, lasers, and integrated circuits (ICs) using TMDCs