Optoelectrical Properties of Transparent Conductive Films Fabricated with Ag Nanoparticle-Suspended Emulsion under Various Formulations and Coating Conditions.

Transparent conductive films (TCFs) were fabricated through bar-coating with a water-in-toluene emulsion containing Ag nanoparticles (AgNPs). Morphological changes in the self-assembled TCF networks under different emulsion formulations and coating conditions and the corresponding optoelectrical properties were investigated. In preparing various emulsions, the concentration of AgNPs and the water weight fraction were important factors for determining the size of the water droplets, which plays a decisive role in controlling the optoelectrical properties of the TCFs affected by open cells and conductive lines. An increased concentration of AgNPs and decreased water weight fraction resulted in a decreased droplet size, thus altering the optoelectrical properties. The coating conditions, such as coating thickness and drying temperature, changed the degree of water droplet coalescence due to different emulsion drying rates, which also affected the final self-assembled network structure and optoelectrical properties of the TCFs. Systematically controlling various material and process conditions, we explored a coating strategy to enhance the optoelectrical properties of TCFs, resulting in an achieved transmittance of 86 ± 0.2%, a haze of 4 ± 0.2%, and a sheet resistance of 35 ± 2.8 Ω/□. TCFs with such optimal properties can be applied to touch screen fields.

Effective decellularization of human skin tissue for regenerative medicine by supercritical carbon dioxide technique.

Allotransplantation, performed using an acellular dermal matrix (ADM), plays a significant role in the cultivation of constituted and damaged organs in clinical. Herein, we fabricated an innovative ADM for allografting derived from decellularized human skin by utilizing the supercritical fluid of carbon dioxide to eliminate immunogenic components. By using histological staining, the ADM product demonstrated the successful removal of cellular constituents without exerting any harmful influence on the extracellular matrix. The results from DNA electrophoresis also supported this phenomenon by showing the complete DNA removal in the product, accompanied by the absence of Major Histocompatibility Complex 1, which suggested the supercritical fluid is an effective method for cellular withdrawal. Moreover, the mechanical property of the ADM products, which showed similarity to that of native skin, displayed great compatibility for using our human-derived ADM as an allograft in clinical treatment. Specifically, the cell viability demonstrated the remarkable biocompatibility of the product to human bio-cellular environment which was noticeably higher than that of other products. Additionally, the significant increase in the level of growth factors such as vascular endothelial growth factor, urokinase-type plasminogen activator receptor, granulocyte-macrophage colony-stimulating factor suggested the ability to stimulate cellular processes, proving the products to be innovative in the field of regeneration when applied to clinical in the future. This study provides a thoroughly extensive analysis of the new ADM products, enabling them to be applied in industrial and clinical treatment.

CO2 doping of organic interlayers for perovskite solar cells.

In perovskite solar cells, doped organic semiconductors are often used as charge-extraction interlayers situated between the photoactive layer and the electrodes. The π-conjugated small molecule 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9-spirobifluorene (spiro-OMeTAD) is the most frequently used semiconductor in the hole-conducting layer1-6, and its electrical properties considerably affect the charge collection efficiencies of the solar cell7. To enhance the electrical conductivity of spiro-OMeTAD, lithium bis(trifluoromethane)sulfonimide (LiTFSI) is typically used in a doping process, which is conventionally initiated by exposing spiro-OMeTAD:LiTFSI blend films to air and light for several hours. This process, in which oxygen acts as the p-type dopant8-11, is time-intensive and largely depends on ambient conditions, and thus hinders the commercialization of perovskite solar cells. Here we report a fast and reproducible doping method that involves bubbling a spiro-OMeTAD:LiTFSI solution with CO2 under ultraviolet light. CO2 obtains electrons from photoexcited spiro-OMeTAD, rapidly promoting its p-type doping and resulting in the precipitation of carbonates. The CO2-treated interlayer exhibits approximately 100 times higher conductivity than a pristine film while realizing stable, high-efficiency perovskite solar cells without any post-treatments. We also show that this method can be used to dope π-conjugated polymers.

Genetic Characterization of Clostridium botulinum Isolated from the First Case of Infant Botulism in Korea.

Botulism is a neuroparalytic disease caused by a neurotoxin produced by Clostridium botulinum. This study aimed to genetically characterize C. botulinum strain isolated from the first case of infant botulism in Korea reported on June 17, 2019. We isolated C. botulinum strain CB-27 from a stool sample of the patient and analyzed the toxin types and toxin gene cluster compositions of the strain using a mouse bioassay, real-time PCR, and genome sequencing. Toxin gene cluster analysis showed that strain CB-27 possesses a C. botulinum neurotoxin type A harboring an unexpressed B gene. Although the nucleotide and amino acid sequences of toxin genes as well as the toxin gene cluster arrangements in strain CB-27 were identical to those of the known strain CDC_69094, the total nucleotide sequences of the toxin gene clusters of CB-27 differed from those of CDC_69094 by 0.47%, indicating genetic diversity of toxin gene clusters of CB-27 among other previously reported C. botulinum strains. To our knowledge, this is the first description of a C. botulinum strain with two separate toxin gene clusters in Korea.

Alleviating oxygen evolution from Li-excess oxide materials through theory-guided surface protection.

Li-excess cathodes comprise one of the most promising avenues for increasing the energy density of current Li-ion technology. However, the first-cycle surface oxygen release in these materials causes cation densification and structural reconstruction of the surface region, leading to encumbered ionic transport and increased impedance. In this work, we use the first principles Density Functional Theory to systematically screen for optimal cation dopants to improve oxygen-retention at the surface. The initial dopant set includes all transition metal, post-transition metal, and metalloid elements. Our screening identifies Os, Sb, Ru, Ir, or Ta as high-ranking dopants considering the combined criteria, and rationalization based on the electronic structure of the top candidates are presented. To validate the theoretical screening, a Ta-doped Li1.3Nb0.3Mn0.4O2 cathode was synthesized and shown to present initial improved electrochemical performance as well as significantly reduced oxygen evolution, as compared with the pristine, un-doped, system.

Draft Genome Sequence of the First South Korean Clinical Isolate of Burkholderia pseudomallei, H0901.

We report here the draft genome sequence of Burkholderia pseudomallei H0901. This strain was isolated in 2003 from the first melioidosis patient in South Korea.

Construction of Luminescence- and Fluorescence-Tagged Burkholderia pseudomallei for Pathogen Tracking in a Mouse Model.

Molecular imaging is a powerful method for tracking various infectious disease-causing pathogens in host organisms. Currently, a dual molecular imaging method that can provide temporal and spatial information on infected hosts at the organism, organ, tissue, and cellular levels simultaneously has not been reported for Burkholderia pseudomallei, a high-risk pathogen that causes melioidosis. In this study, we have established an experimental method that provides spatiotemporal information on infected hosts using luminescent and fluorescent dual-labeled B. pseudomallei. Using this method, we visualized B. pseudomallei infection at the organism, organ, and tissue levels in a BALB/c mouse model by detecting its luminescence and fluorescence. The infection of B. pseudomallei at the cellular level was also visualized by its emitted fluorescence in infected macrophage cells. This method could be an extremely useful and applicable tool to study the pathogenesis of B. pseudomallei-related infectious diseases.

Surface Morphology and Surface Stability against Oxygen Loss of the Lithium-Excess Li2MnO3 Cathode Material as a Function of Lithium Concentration.

There is a growing appreciation for the role of surface reactivity and subsequent reconstruction affecting the performance of high-voltage, high-capacity Li-ion cathode materials. In particular, the promising Li-excess materials are known to exhibit significant vulnerability toward oxygen release, which can cause surface densification and impede Li intercalation. Here we focus on the end member, Li2MnO3, as a Li-excess, Mn-rich representative of this class of materials and systematically elucidate all possible stoichiometric low Miller index surfaces with various cation ordering on each surface. We apply surface cation reconstruction rules that depend on the local environment, including target Mn-Li site exchanges, and optimize the resulting surface Li configurations using metadynamics. The equilibrium Wulff shape shows dominant (001), (010) surface facets, and almost all facets exhibit favorable Mn reconstruction. Most importantly, we find that while all equilibrium LixMnO3 surfaces become unstable toward oxygen release for x < 1.7, some facets are consistently more resistant than others which may provide a design metric for more stable particle morphologies and enhanced surface oxygen retention.

Combinatorial design of copolymer donor materials for bulk heterojunction solar cells.

Seeking π-conjugated polymers with targeted optical band gaps is not only a grand scientific challenge but also in great practical need for systematically improving the performance of organic optoelectronic devices. This work presents a generic combinatorial band-gap design strategy over 780 different copolymer donor materials for bulk heterojunction solar cell applications. Predicted optical band gaps effectively cover the entire solar spectrum from infrared, to visible, to ultraviolet. Combined with empirical arguments widely acknowledged in the literature, the optimal copolymer structures are identified for both single and tandem cells with the optimal power conversion efficiencies.

Structure and optical bandgap relationship of π-conjugated systems.

In bulk heterojunction photovoltaic systems both the open-circuit voltage as well as the short-circuit current, and hence the power conversion efficiency, are dependent on the optical bandgap of the electron-donor material. While first-principles methods are computationally intensive, simpler model Hamiltonian approaches typically suffer from one or more flaws: inability to optimize the geometries for their own input; absence of general, transferable parameters; and poor performance for non-planar systems. We introduce a set of new and revised parameters for the adapted Su-Schrieffer-Heeger (aSSH) Hamiltonian, which is capable of optimizing geometries, along with rules for applying them to any [Formula: see text]-conjugated system containing C, N, O, or S, including non-planar systems. The predicted optical bandgaps show excellent agreement to UV-vis spectroscopy data points from literature, with a coefficient of determination [Formula: see text], a mean error of -0.05 eV, and a mean absolute deviation of 0.16 eV. We use the model to gain insights from PEDOT, fused thiophene polymers, poly-isothianaphthene, copolymers, and pentacene as sources of design rules in the search for low bandgap materials. Using the model as an in-silico design tool, a copolymer of benzodithiophenes along with a small-molecule derivative of pentacene are proposed as optimal donor materials for organic photovoltaics.

Expression and characterization of an iron-containing superoxide dismutase from Burkholderia pseudomallei.

A superoxide dismutase (SOD) gene from Burkholderia pseudomallei, the causative agent of melioidosis, was cloned and expressed in Escherichia coli, and its product was functionally and physically characterized. The gene has an open-reading frame of 579 bp. The deduced amino acid sequence has 192 residues with a calculated molecular mass of ~22 kDa. Sequence comparison with other bacterial SODs showed that the protein contains typical metal-binding motifs and other Fe-SOD-conserved residues. The sequence has substantial similarity with other bacterial Fe-SOD sequences. The enzymatic activity of the expressed protein was inhibited by hydrogen peroxide but not by sodium azide or potassium cyanide, attributes that indeed are characteristic of typical bacterial Fe-SODs. Western blotting with antiserum against the recombinant Fe-SOD revealed that it is expressed in B. pseudomallei. Transformed E. coli that expressed the Fe-SOD had significantly increased SOD activity and was highly tolerant to paraquat-mediated replication inhibition, compared to transformed cells carrying an empty vector. Our results provide a basis for further biochemical characterization of the enzyme and elucidation of its role in the pathogenesis of B. pseudomallei.

Self-localized domain walls at π-conjugated branching junctions.

Self-localized domain walls are found trapped at the potential wells created by π-conjugated branching junctions due to the intrinsic electron-phonon couplings. The potential well depths are 0.14 eV for soliton, 0.28 eV for polaron, and 0.32 eV for exciton using the adapted Su-Schrieffer-Heeger model Hamiltonian, as compared to 0.23 eV for soliton, 0.25 eV for positively charged polaron, 0.33 eV for negatively charged polaron, and 0.21 eV for exciton using the ab initio Hartree-Fock method. Once the junction trapping wells are filled, however, branching junctions turn repulsive to additional self-localized domain walls. Torsions around the branching junction center have significant effects on the junction band gap and electron localizations.

Unified Hamiltonian for conducting polymers.

Two transferable physical parameters are incorporated into the Su-Schrieffer-Heeger Hamiltonian to model conducting polymers beyond polyacetylene: the parameter γ scales the electron-phonon coupling strength in aromatic rings and the other parameter ε specifies the heterogeneous core charges. This generic Hamiltonian predicts the fundamental band gaps of polythiophene, polypyrrole, polyfuran, poly-(p-phenylene), poly-(p-phenylene vinylene), and polyacenes, and their oligomers of all lengths, with an accuracy exceeding time-dependent density functional theory. Its computational costs for moderate-length polymer chains are more than eight orders of magnitude lower than first-principles approaches.

Semicrystalline thermoplastic elastomeric polyolefins: Advances through catalyst development and macromolecular design.

We report the design, synthesis, morphology, phase behavior, and mechanical properties of semicrystalline, polyolefin-based block copolymers. By using living, stereoselective insertion polymerization catalysts, syndiotactic polypropylene-block-poly(ethylene-co-propylene)-block-syndiotactic polypropylene and isotactic polypropylene-block-regioirregular polypropylene-block-isotactic polypropylene triblock copolymers were synthesized. The volume fraction and composition of the blocks, as well as the overall size of the macromolecules, were controlled by sequential synthesis of each block of the polymers. These triblock copolymers, with semicrystalline end-blocks and mid-segments with low glass-transition temperatures, show significant potential as thermoplastic elastomers. They have low Young's moduli, large strains at break, and better than 90% elastic recovery at strains of 100% or less. An isotactic polypropylene-block-regioirregular polypropylene-block-isotactic polypropylene-block-regioirregular polypropylene-block-isotactic polypropylene pentablock copolymer was synthesized that also shows exceptional elastomeric properties. Notably, microphase separation is not necessary in the semicrystalline isotactic polypropylenes to achieve good mechanical performance, unlike commercial styrenic thermoplastic elastomers.

The relationship between polymer/substrate charge density and charge overcompensation by adsorbed polyelectrolyte layers.

This work examines polyelectrolyte adsorption (exclusively driven by electrostatic attractions) for a model system (DMAEMA, polydimethylaminoethyl methacrylate, adsorbing onto silica) where the adsorbing polycation is more densely charged than the substrate. Variations in the relative charge densities of the polymer and substrate are accomplished by pH, and the polycation is of sufficiently low molecular weight that the adsorbed conformation is generally flat under all conditions examined. We demonstrate, quantitatively, that the charge overcompensation observed on the isotherm plateau can be attributed to the denser positive charge on the adsorbing polycation and that the ultimate coverage obtained corresponds to the adsorption of one oligomer onto each original negative silica charge, when the silica charge is most sparse, at pH 6. This limiting behavior breaks down at higher pHs where the greater silica charge density accommodates single chains adsorbing onto multiple negative sites. As a result of the greater substrate charge density and reduced polycation charge at higher pHs, the extent of charge overcompensation diminishes while the coverage increases on the plateau of the isotherm. Ultimately at the highest pHs, a regime is approached where the coil's excluded surface area, not surface charge, limits the ultimate coverage. In addition to quantifying the crossover from the charge-limiting to the area-limiting behaviors, this paper quantitatively reports adsorption-induced changes in bound counterion density and ionization at the interface, which were generally found to be independent of coverage for this model system.