Two-Dimensional Stacked Composites of Self-Assembled Alkane Layers and Graphene for Transparent Gas Barrier Films with Low Permeability.

Self-assembled alkane layers are introduced between graphene layers to physically block nanometer size defects in graphene and lateral gas pathways between graphene layers. A well-defined hexatriacontane (HTC) monolayer on graphene could cover nanometer-size defects because of the flexible nature and strong intermolecular van der Waals interactions of alkane, despite the roughness of graphene. In addition, HTC multilayers between graphene layers greatly improve their adhesion. This indicates that HTC multilayers between graphene layers can effectively block the lateral pathway between graphene layers by filling open space with close-packed self-assembled alkanes. By these mechanisms, alternately stacked composites of graphene and self-assembled alkane layers greatly increase the gas-barrier property to a water vapor transmission rate (WVTR) as low as 1.2 × 10-3 g/(m2 day), whereas stacked graphene layers generally show a WVTR < 0.5 g/(m2 day). Furthermore, the self-assembled alkane layers have superior crystallinity and wide bandgap, so they have little effect on the transmittance.

Structural Responses Estimation of Cable-Stayed Bridge from Limited Number of Multi-Response Data.

A cable-stayed bridge is widely adopted to construct long-span bridges. The deformation of cable-stayed bridges is relatively larger than that of conventional bridges, such as beam and truss types. Therefore, studies regarding the monitoring systems for cable-stayed bridges have been conducted to evaluate the performance of bridges based on measurement data. However, most studies required sufficient measurement data for evaluation and just focused on the local response estimation. To overcome these limitations, Structural Responses Analysis using a Limited amount of Multi-Response data (SRALMR) was recently proposed and validated with the beam and truss model that has a simple structural behavior. In this research, the structural responses of a cable-stayed bridge were analyzed using SRALMR. The deformed shape and member internal forces were estimated using a limited amount of displacement, slope, and strain data. Target structural responses were determined by applying four load cases to the numerical model. In addition, pre-analysis for initial shape analysis was conducted to determine the initial equilibrium state, minimizing the deformation under dead loads. Finally, the performance of SRALMR for cable-stayed bridges was analyzed according to the combination and number of response data.

Single-Crystal Poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b']dithiophen-2-yl)- alt-[1,2,5]thiadiazolo[3,4- c]pyridine] Nanowires with Ultrahigh Mobility.

We fabricated single-crystal poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b']-dithiophen-2-yl)- alt-[1,2,5]thiadiazolo-[3,4- c]pyridine] (PCDTPT) nanowires with ultrahigh mobility using a liquid-bridge-mediated nanotransfer molding method. The structural analysis of the single-crystal PCDTPT nanowires reveals that PCDTPT crystals have a triclinic structure, and the nanowires grow parallel to PCDTPT backbone chains, which provide important insights into its intrinsic charge transport. The single-crystal PCDTPT nanowire exhibits a superior charge carrier mobility of 72.94 ± 18.02 cm2 V-1 s-1 (maximum mobility up to 92.64 cm2 V-1 s-1), which is a record high value among conjugated polymers to date. In the single-crystal PCDTPT nanowire, the backbone chains in the linear structure along the nanowire growth axis lead to strong backbone delocalization, resulting in highly conductive polymer backbones and a drastic increase in charge carrier mobility. In addition, the single-crystal PCDTPT nanowire shows good environmental stability under air conditions compared to small-molecule organic semiconductors.

Optical, Electrochemical and Thermal Studies of Conjugated Polymers Synthesized by Eutectic Melt Reaction.

This paper reports on the synthesis of a novel donor-acceptor conjugated polymers, P1 and P2 by solvent free eutectic melt polymerization reaction. Triisopropylsilylethynyl(TIPS) substituted benzo[1,2-b:4,5-b']dithiophene(BDT) is used as donor, thienithiophene(TT) and thienopyrroledione(TPD) are utilized as acceptors for demonstrating eutectic polymerization. The most important fact in the solvent-free reaction between solid reactants actually proceeds through bulk liquid phases. Such liquid phases are possible due to the formation of eutectics between the reactants and product(s) and any evolution of heat. Naphthalene is explored in this reaction for forming eutectics with the reactants, resulting in desired polymers. Thermal stability, optical and electrochemical properties of these polymers were determined. Optical band gaps of the polymers were found to be 1.58 and 1.65 eV. Electrochemical studies by cyclic voltametry experiment revealed HOMO and LUMO energy levels to be -5.22, -5.60 eV, and -3.76, -4.16 eV, respectively. The polymers were thermally stable up to 285-400 °C. Thermal, optical and electrochemical studies indicated these materials to be promising candidates in organic electronic applications.

Synthesis and Photophysical Studies of Thiadiazole[3,4-c]pyridine Copolymer Based Organic Field-Effect Transistors.

A novel thiadiazolo[3,4-c]pyridine] based donor-acceptor (D-A) copolymer, poly[4,8-bis(triisopropylsilylethynyl)benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-[4,7-bis(4-(2-ethylhexyl)thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-c]pyridine] (PTBDTPT), containing triisopropylsilylethynyl(TIPS)benzo[1,2-b:4,5-b']dithiophene as a donor is synthesized by Stille polymerization reaction. All the important photo physical prerequisites for organic field-effect transistor (OFET) application such as strong and broad optical absorption, thermal stability, and compatible HOMO-LUMO levels can be accomplished and combined on one macromolecule. Optical band gap of the polymer was found to be 1.61 eV as calculated from its film onset absorption edge. The hole mobility of bottom gate OFET using the synthesized polymer as an active channel is found to be 1.92 X 10(-2) cm V(-1) s(-1) with the On/Off ratio of 25. The photophysical study suggests that PTBDTPT is promising candidate for future large area organic electronic applications.

Synthesis, Characterization and Optoelectronic Properties of Benzodithiophene Based Copolymers for Application in Solar Cells.

This paper reports on the synthesis and characterization of novel donor-acceptor (D-A) conjugated polymers containing triisopropylsilylethyny(TIPS)benzo[1,2-b:4,5-b']dithiophene-diketopyrrolopyrrole (P1 and P2) through Stille co-polymerization method. Thermal stability, optical and electrochemical properties of these polymers were determined. Optical band gaps of the polymers as calculated from their film onset absorption edges were found to be 1.46 and 1.44 eV, respectively. Electrochemical studies revealed HOMO and LUMO energy levels to be -5.22, -5.60 eV, and -3.76, -4.16 eV, respectively. The polymers were thermally stable up to 400-440 °C. Optoelectronic studies indicated that these materials to be promising candidates in solar cell applications.

Synthesis, Characterization and TFT Characteristics of Diketopyrrolopyrrole Based Copolymer.

A novel diketopyrrolopyrrole (DPP) based low band gap polymer, poly[4,8-bis(triisopropylsilylethynyl) benzo[1,2-b:4,5-b']dithiophene-2,6-diyl-alt-[2,5-di-hexyl-3,6-dithiophen-2-ylpyrrolo[3,4-c]pyrrole-1,4-dione] (PTIPSBDT-DPP) is synthesized by Stille polymerization for use in thin film transistor (TFTs). The new polymer contain extended aromatic π-conjugated segments alternating with the DPP units and are designed to increase the free energy for charge generation to overcome current limitations in photocurrent generation. In this study we describe the synthesis, thermal stability, optical, electrochemical properties and TFT characteristics.

Heterogeneous Charge-Transfer Nanorods by Strained Melt-Molding Lithography.

Hetero-nanorods consisting of two charge-transfer (CT) complexes were fabricated by the strained melt-molding lithography. Utilizing the lowered melting temperature by the formation of eutectic mixture, various well-defined CT complex nanorods can be easily fabricated by soft-lithography-assisted melt crystallization below 100 degrees C. Hetero-nanorods were fabricated by selective doping of the secondary CT complex at defects induced by applying the uniaxial strain.

Cross-stacked single-crystal organic nanowire p-n nanojunction arrays by nanotransfer printing.

We fabricated cross-stacked organic p-n nanojunction arrays made of single-crystal 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-PEN) and fullerene (C60) nanowires as p-type and n-type semiconductors, respectively, by using a nanotransfer printing technique. Single-crystal C60 nanowires were synthesized inside nanoscale channels of a mold and directly transferred onto a desired position of a flexible substrate by a lubricant liquid layer. In the consecutive printing process, single-crystal TIPS-PEN nanowires were grown in the same way and then perpendicularly aligned and placed onto the C60 nanowire arrays, resulting in a cross-stacked single-crystal organic p-n nanojunction array. The cross-stacked single-crystal TIPS-PEN/C60 nanowire p-n nanojunction devices show rectifying behavior with on/off ratio of ∼ 13 as well as photodiode characteristic with photogain of ∼ 2 under a light intensity of 12.2 mW/cm(2). Our study provides a facile, solution-processed approach to fabricate a large-area array of organic crystal nanojunction devices in a desired arrangement for future nanoscale electronics.

Observation of Charge Separation and Space-Charge Region in Single-Crystal P3HT/C60 Heterojunction Nanowires.

We directly observed charge separation and a space-charge region in an organic single-crystal p-n heterojunction nanowire, by means of scanning photocurrent microscopy. The axial p-n heterojunction nanowire had a well-defined planar junction, consisted of P3HT (p-type) and C60 (n-type) single crystals and was fabricated by means of the recently developed inkjet-assisted nanotransfer printing technique. The depletion region formed at the p-n junction was directly observed by exploring the spatial distribution of photogenerated carriers along the heterojunction nanowire under various applied bias voltages. Our study provides a facile approach toward the precise characterization of charge transport in organic heterojunction systems as well as the design of efficient nanoscale organic optoelectronic devices.

Formamidinium Lead Iodide Perovskite Thin Films Formed by Two-Step Sequential Method: Solvent-Morphology Relationship.

Thin films made of formamidinium lead iodide (FAPbI3) perovskites prepared by a two-step sequential deposition method using various solvents for formamidinium iodide (FAI) - isopropanol, n-butanol and tert-butanol, were studied with the aim of finding a correlation between morphology and solvent properties to improve film quality. They were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and their photophysical properties were studied by means of absorption and photoluminescence (PL) spectroscopies. XRD patterns, absorption and PL spectra proved α-phase formation for all selected solvents. An excessive amount of PbI2 found in perovskite films prepared with n-butanol indicates incomplete conversion. Thin film morphology, such as grain and crystallite size, depended on the solvent. Using tert-butanol, thin films with a very large grain size of up to several micrometers and with preferred crystallite orientation were fabricated. The grain size increased as follows: 0.2-0.5, 0.2-1 and 2-5 µm for isopropanol, n-butanol and tert-butanol, respectively. A correlation between the grain size and viscosity, electric permittivity and polarizability of the solvent could be considered. Our results, including fabrication of perovskite films with large grains and fewer grain boundaries, are important and of interest for many optoelectronic applications.

Effects of the Donor Unit on the Formation of Hybrid Layers of Donor-Acceptor Copolymers with Silver Nanoparticles.

Donor-acceptor (D-A) copolymers containing perylene-3,4,9,10-tetracarboxydiimide (PDI) electron-acceptor (A) units belonging to n-type semiconductors are of interest due to their many potential applications in photonics, particularly for electron-transporting layers in all-polymeric or perovskite solar cells. Combining D-A copolymers and silver nanoparticles (Ag-NPs) can further improve material properties and device performances. Hybrid layers of D-A copolymers containing PDI units and different electron-donor (D) units (9-(2-ethylhexyl)carbazole or 9,9-dioctylfluorene) with Ag-NPs were prepared electrochemically during the reduction of pristine copolymer layers. The formation of hybrid layers with Ag-NP coverage was monitored by in-situ measurement of absorption spectra. The Ag-NP coverage of up to 41% was higher in hybrid layers made of copolymer with 9-(2-ethylhexyl)carbazole D units than in those made of copolymer with 9,9-dioctylfluorene D units. The pristine and hybrid copolymer layers were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy, which proved the formation of hybrid layers with stable Ag-NPs in the metallic state with average diameters <70 nm. The influence of D units on Ag-NP diameters and coverage was revealed.

Synthesis of MAPbBr3 -Polymer Composite Films by Photolysis of DMF: Toward Transparent and Flexible Optical Physical Unclonable Functions (PUFs) with Hierarchical Multilevel Complexity.

Physical entities with inherent randomness have been investigated as anti-counterfeiting labels based on physical unclonable functions (PUFs). Herein, a transparent and flexible optical PUF label associated with multilevel complexity is demonstrated by taking advantage of the optical properties of hierarchical morphologies of the composite film composed of metal halide perovskite nanoparticles (MAPbBr3 NPs) and the intrinsic spinodal-decomposition-like phase separation of polymer blend (PMMA/PS blend). Due to the combinatorial effects of the photolysis synthesis of MAPbBr3 and the thermodynamic instability of the PMMA/PS blend, randomized patterns emerge at two-level scales. These patterns are intrinsically non-deterministic, and therefore, the PUF labels from the multilevel random patterns are challenging to replicate. This is mainly attributed to random spot patterns (higher-level patterns) confined within intricate bicontinuous patterns (lower-level patterns).

Significant boost of the stability and PLQYof CsPbBr3 NCs by Cu-BTC MOF.

Developing stable perovskite nanocrystals (NCs) with enhancing luminescent properties holds great importance for future potential applications in optoelectronics. Here, we engaged perovskite NCs in Cu2+ ion-based metal-organic framework (MOF) Cu-BTC (BTC = 1,3,5-benzene tricarboxylate) by physical mixing of MOF with CsPbBr3 NCs in toluene solution. MOF-protected perovskite NCs achieved high photoluminescence quantum yield 96.51% than pristine state CsPbBr3 NCs (51.66%). Along with the improvement in optical properties, the long-term stability of CsPbBr3 NCs in the solution phase also increases considerably upon loading in Cu-BTC MOF. Moreover, the changes in the luminescent intensity of the samples have been observed for 3 months in the solution. After 1 month, pristine CsPbBr3 NCs lose their emission intensity 68% from the initial, while the MOF-protected CsPbBr3 NCs show only a 10% reduction from the initial. These results indicate that the effective passivation of Cu-BTC MOF inhibits the aggregation of NCs, protecting them from the defective atmosphere. The excellent photoluminescence findings provide a new pathway for future optoelectronic applications.

Types and Characteristics of Fatal Accidents Caused by Multiple Processes in a Workplace: Based on Actual Cases in South Korea.

As the social cost of disasters increases and safety is being emphasized, policy regulations at the national level have been implemented. However, various fatal accidents are continually occurring as continued economic development and enhanced technologies have increased demand and complicated the industrial structure. Workers in different industries, performing similar jobs, often experience different workplace hazards, which can result in similar types of accidents. Therefore, new policy regulations have been established to separate multiple processes and work in workplaces and are being implemented in several countries to minimize damage caused by new types of industrial accidents. Supervision and management appropriate for contractors or safety and health officials with legal obligations are required to play a regulatory role when these types of industrial accidents are likely to occur. This study classified accidental types and their characteristics based on actual cases, in which potential risks exist at multiple processes in a workplace. First, raw data of work-related fatalities that occurred in South Korea were reviewed and classified as fatal accidents caused by multiple processes in workplaces using the proposed method. Next, the classified actual cases were prepared as statistical data and analyzed based on the various categories. Finally, the accident type based on multiple processes, including risks and characteristics, in workplaces was proposed. As a result, this study improved the safety awareness and understanding of regulatory subjects regarding industrial accidents caused by multiple processes in workplaces and is expected to improve the effectiveness of the existing policy to prevent workplace accidents.

Polymers based on thieno[3,4-c]pyrrole-4,6-dione and pyromellitic diimide by CH-CH arylation reaction for high-performance thin-film transistors.

Three homopolymers were successfully synthesized by direct CH-CH arylation polymerization of thieno[3,4-c]pyrrole-4,6-dione or pyromellitic diimide derivatives affording highly purified polymers with high molecular weights (43.0-174.7 K). Thieno[3,4-c]pyrrole-4,6-dione and pyromellitic diimide derivatives are considered as electron-withdrawing units. The synthesized homopolymers P1, P2, and P3 showed band gaps in the range of 2.13-2.08 eV, respectively. The electron mobilities of the three homopolymers have been investigated. The thin film transistor for P1 prepared by the eutectic-melt-assisted nanoimprinting method achieved an electron mobility of 2.11 × 10-3 cm2 s-1 V-1. Based on the obtained results, the synthesized polymers can be used as potential electron acceptors in solar cell applications.

Visualization of nonsingular defect enabling rapid control of structural color.

Stimuli-interactive structural color (SC) of a block copolymer (BCP) photonic crystal (PC) uses reversible alteration of the PC using external fluids and applied forces. The origin of the diffusional pathways of a stimulating fluid into a BCP PC has not been examined. Here, we directly visualize the vertically oriented screw dislocations in a one-dimensional lamellar BCP PC that facilitate the rapid response of visible SC. To reveal the diffusional pathway of the solvent via the dislocations, BCP lamellae are swollen with an interpenetrated hydrogel network, allowing fixation of the swollen state and subsequent microscopic examination. The visualized defects are low-energy helicoidal screw dislocations having unique, nonsingular cores. Location and areal density of these dislocations are determined by periodic concentric topographic nanopatterns of the upper surface-reconstructed layer. The nonsingular nature of the interlayer connectivity in the core region demonstrates the beneficial nature of these defects on sensing dynamics.

Hybrid Layers of Donor-Acceptor Copolymers with Homogenous Silver Nanoparticle Coverage for Photonic Applications.

Hybrid layers of donor-acceptor (D-A) copolymers containing N,N'-dialkylperylene-3,4,9,10-tetracarboxydiimide electron-acceptor units covered with silver nanoparticles (Ag-NPs) were prepared by electrochemical doping of pristine layers during reduction processes. In situ optical absorption spectra of the layers were recorded during the formation of Ag-NP coverage. The hybrid layers were characterized by absorption spectroscopy, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray spectroscopy (EDX). In the absorption spectra of the hybrid layers, a surface plasmon band characteristic of Ag-NPs appeared. Significant improvements in light absorption due to the plasmonic effects of Ag NPs were observed. Stable Ag-NPs with an average diameter of 41-63 nm were formed on the surface, as proven by SEM and XPS. The Ag-NP coverage and size depended on the hybrid layer preparation conditions and on the copolymer composition. The metallic character of the Ag-NPs was proven by XPS. The location in the surface layer was further confirmed by EDX analysis. To the best of our knowledge, this is the first report on such hybrid layers having the potential for a variety of photonic and electronic applications.

Suggestion of an Improved Evaluation Method of Construction Companies' Industrial Accident Prevention Activities in South Korea.

Workers in the construction industry are constantly exposed to dangers during work that can lead to death or disability. Despite recent advances in construction technology, the presence of these risks for workers has become an unresolved social problem. In particular, most companies often recognize that it is necessary to mitigate against risks posed to worker only after an accident has occurred. Recently, there has been an increasing demand for the development of new safety technologies and policy proposals to ensure the safety of workers during construction or work. However, the right solution is not coping after an accident but preventing it, and this must be accompanied by voluntary efforts by the company. To work toward such solutions, Korea is implementing an evaluation of construction companies' industrial accident prevention activities without legal regulations or coercion to encourage voluntary accident prevention activities by companies. The purpose of this study is to propose an effective improvement direction for the system implemented by the Korea Occupational Safety and Health Agency. First, by analyzing the details of the system and the data of the evaluation results, the system's effectiveness and rationality are reviewed, and steps for improvement are determined. Next, an evaluation model is proposed considering the size of the company to be evaluated and the level of safety and health, and its validity is verified through a survey of construction workers. Finally, a plan to induce the voluntary participation of construction companies in this system and the role of the supervisory authority are presented. This study is expected to serve as an important example of an effective safety policy model by encouraging companies' voluntary efforts to prevent accidents in the construction industry and raise the level of potential safety and health awareness.

Transesterification in Vitrimer Polymers Using Bifunctional Catalysts: Modeled with Solution-Phase Experimental Rates and Theoretical Analysis of Efficiency and Mechanisms.

Recently, thermoset vitrimer polymers have shown significant promise for structural applications because of their ability to be reshaped and remolded due to their covalent adaptive network (CAN). In these vitrimers, the transesterification reaction is responsible for the CAN, where the efficiency of the reaction is controlled either by organic or by organometallic catalysts. Understanding the mechanism of the transesterification reaction in the bulk phase using direct experimental techniques is extremely difficult due to the highly cross-linked complex structure of thermosetting vitrimers. Therefore, we use solution-phase experiments to investigate the catalytic efficiency and to guide density functional theory (DFT) simulations of the transesterification reaction mechanism with catalysts triazabicyclodecene (TBD), zinc acetate (Zn(OAc)2), 1-methylimidazole (1-MI), and dibutyltin oxide (DBTO). The estimated catalytic efficiency from the detailed DFT reaction path calculations follows the order TBD ≳ DBTO ≳ Zn(OAc)2 > 1-MI, which agrees with the experimental results. In addition to reaction path modeling, the mechanism and the relative rates of the transesterification reaction are analyzed with the assistance of Fukui indices as a measure of electrophilicity and nucleophilicity of atomic sites and with partial charges. It was found that the sum of the nucleophilicity index of the base and the electrophilicity index of the acid of the bifunctional catalysts correlates with the SN2 transition state and tetrahedral intermediate energies, which are related to the barrier of the rate-limiting step. This correlation provides a hypothesis for computational prescreening of potentially better catalysts that have an index in a range of values. These results provide a basis for understanding an important part of the mechanism of transesterification in vitrimer systems and may assist with designing new catalysts.