Stiffer but More Healable Exponential Layered Assemblies with Boron Nitride Nanoplatelets

Self-healing ability and the elastic modulus of polymeric materials may seem conflicting because of their opposite dependence on chain mobility. Here, we show that boron nitride (BN) nanoplatelets can simultaneously enhance these seemingly contradictory properties in exponentially layer-by-layer-assembled nanocomposites as both surface coatings and free-standing films. On one hand, embedding hard BN nanoplatelets into a soft hydrogen bonding network can enhance the elastic modulus and ultimate strength through effective load transfer strengthened by the incorporation of interfacial covalent bonding; on the other hand, during a water-enabled self-healing process, these two-dimensional flakes induce an anisotropic diffusion, maintain the overall diffusion ability of polymers at low loadings, and can be “sealing” agents to retard the out-of-plane diffusion, thereby hampering polymer release into the solution. A detailed mechanism study supported by a theoretical model reveals the critical parameters for achieving a complete self-healing process. The insights gained from this work may be used for the design of high-performance smart materials based on other two-dimensional fillers

Statistical effects of pore features on mechanical properties and fracture behaviors of heterogeneous random porous materials by phase-field modeling

Heterogeneous materials with randomly distributed pores are ubiquitous, such as sintered silver nanoparticles, concrete materials, 3D printed polymers, and natural bones. Recent experimental investigations have revealed that porosity and also pore-related geometries (size, number, shape, distribution and alignment) have significant impacts on the mechanical behavior of random porous materials. However, existing studies focus on the porosity effect while ignoring other pore features such as pore size and pore shape. Our research is dedicated to a computational framework for generating isotropic/anisotropic random porous materials using Gaussian random fields with stochastic pore size and shape factor and addressing the mechanical properties and behavior of brittle fractures using a fracture phase-field model with a preferred degradation function. Sintered silver nanoparticles with typical randomly distributed pores, as representative porous materials, are chosen for their promising applications in emerging fields such as power electronics and wearable devices. In order to emphasize the effect of pore size and shape, 420 random samples with a fixed porosity were generated to discuss the stress–strain response during fracture and to establish statistical relationships between pore feature distributions and mechanical properties such as Young's modulus, UTS, and average historical energy. Our findings suggest that the statical attributes of the pore sizes and shape factors significantly affect the material performance related to the mechanical properties and fracture behavior, which could give a better understanding of the random porous materials and guide reliability-based material design optimization

Strong and Stiff Aramid Nanofiber/Carbon Nanotube Nanocomposites

Small but strong carbon nanotubes (CNTs) are fillers of choice for composite reinforcement owing to their extraordinary modulus and strength. However, the mechanical properties of the nanocomposites are still much below those for mechanical parameters of individual nanotubes. The gap between the expectation and experimental results arises not only from imperfect dispersion and poor load transfer but also from the unavailability of strong polymers that can be effectively utilized within the composites of nanotubes. Aramid nanofibers (ANFs) with analogous morphological features to nanotubes represent a potential choice to complement nanotubes given their intrinsic high mechanical performance and the dispersible nature, which enables solvent-based processing methods. In this work, we showed that composite films made from ANFs and multiwalled CNTs (MWCNTs) by vacuum-assisted flocculation and vacuum-assisted layer-by-layer assembly exhibited high ultimate strength of up to 383 MPa and Young’s modulus (stiffness) of up to 35 GPa, which represent the highest values among all the reported random CNT nanocomposites. Detailed studies using different imaging and spectroscopic characterizations suggested that the multiple interfacial interactions between nanotubes and ANFs including hydrogen bonding and π–π stacking are likely the key parameters responsible for the observed mechanical improvement. Importantly, our studies further revealed the attractive thermomechanical characteristics of these nanocomposites with high thermal stability (up to 520 °C) and ultralow coefficients of thermal expansion (2–6 ppm·K^–1). Our results indicated that ANFs are promising nanoscale building blocks for functional ultrastrong and stiff materials potentially extendable to nanocomposites based on other nanoscale fillers

One-Pot Approach to 1,2-Disubstituted Indoles via Cu(II)-Catalyzed Coupling/Cyclization under Aerobic Conditions and Its Application for the Synthesis of Polycyclic Indoles

A straightforward assembly of 1,2-disubstituted indoles has been developed through a Cu­(II)-catalyzed domino coupling/cyclization process. Under aerobic conditions, a wide range of 1,2-disubstituted indole derivatives were efficiently and facilely synthesized from 2-alkynylanilines and boronic acids. 2-(2-Bromoaryl)-1-aryl-1<i>H</i>-indoles, which were selectively generated in one pot under the Cu catalysis, afforded the indolo­[1,2-<i>f</i>]­phenanthridines via Pd-catalyzed intramolecular direct C­(sp²)–H arylation. The one-pot tandem approaches to the polycyclic indole derivatives were also successfully achieved

High-Performance Lossy-Mode Resonance Sensor Based on Few-Layer Black Phosphorus

Surface plasmon resonance (SPR) can be excited only by the transverse magnetic (TM)-polarized light in the conventional SPR sensor, whereas the lossy-mode resonance (LMR) can be achieved with both transverse electric (TE)- and TM-polarized lights. In this work, we propose a high-performance LMR sensor based on few-layer black phosphorus (BP), and the high quality factor (<i>Q</i>) of this BP-based LMR sensor for TE- and TM-polarized lights has been discussed. In comparison with that for the conventional SPR sensor, the <i>Q</i> factor for the proposed BP-based LMR sensor with both TE- and TM-polarized lights has been greatly improved. In particular, the highest <i>Q</i> factor as high as 2 × 10⁵ RIU^–1 can be obtained for the TM-polarized mode

Hydrogen Bonding Stabilized Self-Assembly of Inorganic Nanoparticles: Mechanism and Collective Properties

Developing a simple and efficient method to organize nanoscale building blocks into ordered superstructures, understanding the mechanism for self-assembly and revealing the essential collective properties are crucial steps toward the practical use of nanostructures in nanotechnology-based applications. In this study, we showed that the high-yield formation of ZnO nanoparticle chains with micrometer length can be readily achieved by the variation of solvents from methanol to water. Spectroscopic studies confirmed the solvent effect on the surface properties of ZnO nanoparticles, which were found to be critical for the formation of anisotropic assemblies. Quantum mechanical calculations and all atom molecular dynamic simulations indicated the contribution of hydrogen bonding for stabilizing the structure in water. Dissipative particle dynamics further revealed the importance of solvent–nanoparticle interactions for promoting one-dimensional self-assembly. The branching of chains was found upon aging, resulting in the size increase of the ensembles and network formation. Steady-state and time-resolved luminescent spectroscopes, which probed the variation of defect-related emission, revealed stronger Forster resonance energy transfer (FRET) between nanoparticles when the chain networks were formed. The high efficiency of FRET quenching can be ascribed to the presence of multiple energy transfer channels, as well as the short internanoparticle distances and the dipole alignment

image_3_The Surface-Exposed Protein SntA Contributes to Complement Evasion in Zoonotic Streptococcus suis.jpeg

<p>Streptococcus suis is an emerging zoonotic pathogen causing streptococcal toxic shock like syndrome (STSLS), meningitis, septicemia, and even sudden death in human and pigs. Serious septicemia indicates this bacterium can evade the host complement surveillance. In our previous study, a functionally unknown protein SntA of S. suis has been identified as a heme-binding protein, and contributes to virulence in pigs. SntA can interact with the host antioxidant protein AOP2 and consequently inhibit its antioxidant activity. In the present study, SntA is identified as a cell wall anchored protein that functions as an important player in S. suis complement evasion. The C3 deposition and membrane attack complex (MAC) formation on the surface of sntA-deleted mutant strain ΔsntA are demonstrated to be significantly higher than the parental strain SC-19 and the complementary strain CΔsntA. The abilities of anti-phagocytosis, survival in blood, and in vivo colonization of ΔsntA are obviously reduced. SntA can interact with C1q and inhibit hemolytic activity via the classical pathway. Complement activation assays reveal that SntA can also directly activate classical and lectin pathways, resulting in complement consumption. These two complement evasion strategies may be crucial for the pathogenesis of this zoonotic pathogen. Concerning that SntA is a bifunctional 2′,3′-cyclic nucleotide 2′-phosphodiesterase/3′-nucleotidase in many species of Gram-positive bacteria, these complement evasion strategies may have common biological significance.</p

Protein adsorption on different nanofibrous matrices.

<p>(a) Fluorescence images of the Rhodamine B labelled BSA adsorption on PLGA, PLGA/HA PLGA/GO and PLGA/GO/HA; (b) The adsorption of protein onto the PLGA, PLGA/HA, PLGA/GO and PLGA/GO/HA nanofibrous matrices. (n = 5;* p < 0.05).</p

Proliferation of MC3T3-E1 cells cultured on the nanofibrous matrices for 1 to 7 days in vitro.

<p>P < 0.05, n = 4.</p

image_1_The Surface-Exposed Protein SntA Contributes to Complement Evasion in Zoonotic Streptococcus suis.jpeg

<p>Streptococcus suis is an emerging zoonotic pathogen causing streptococcal toxic shock like syndrome (STSLS), meningitis, septicemia, and even sudden death in human and pigs. Serious septicemia indicates this bacterium can evade the host complement surveillance. In our previous study, a functionally unknown protein SntA of S. suis has been identified as a heme-binding protein, and contributes to virulence in pigs. SntA can interact with the host antioxidant protein AOP2 and consequently inhibit its antioxidant activity. In the present study, SntA is identified as a cell wall anchored protein that functions as an important player in S. suis complement evasion. The C3 deposition and membrane attack complex (MAC) formation on the surface of sntA-deleted mutant strain ΔsntA are demonstrated to be significantly higher than the parental strain SC-19 and the complementary strain CΔsntA. The abilities of anti-phagocytosis, survival in blood, and in vivo colonization of ΔsntA are obviously reduced. SntA can interact with C1q and inhibit hemolytic activity via the classical pathway. Complement activation assays reveal that SntA can also directly activate classical and lectin pathways, resulting in complement consumption. These two complement evasion strategies may be crucial for the pathogenesis of this zoonotic pathogen. Concerning that SntA is a bifunctional 2′,3′-cyclic nucleotide 2′-phosphodiesterase/3′-nucleotidase in many species of Gram-positive bacteria, these complement evasion strategies may have common biological significance.</p