Large-Area Printed Oxide Film Sensors Enabling Ultrasensitive and Dual Electrical/Colorimetric Detection of Hydrogen at Room Temperature.

Commercial hydrogen (H2) sensors operate at high temperatures, which increases power consumption and poses a safety risk owing to the flammable nature of H2. Here, a polymer-noble metal-metal oxide film is fabricated using the spin-coating and printing methods to realize a highly sensitive, low-voltage operation, wide-operating-concentration, and near-monoselective H2 sensor at room temperature. The H2 sensors with an optimized thickness of Pd nanoparticles and SnO2 showed an extremely high response of 16,623 with a response time of 6 s and a recovery time of 5 s at room temperature and 2% H2. At the same time, printed flexible sensors demonstrate excellent sensitivity, with a response of 2300 at 2% H2. The excellent sensing performance at room temperature is due to the optimal SnO2 thickness, corresponding to the Debye length and the oxygen and H2 spillover caused by the optimized coverage of the Pd catalyst. Furthermore, multistructures of WO3 and SnO2 films are used to fabricate a new type of dual-signal sensor, which demonstrated simultaneous conductance and transmittance, i.e., color change. This work provides an effective strategy to develop robust, flexible, transparent, and long-lasting H2 sensors through large-area printing processes based on polymer-metal-metal oxide nanostructures.

Amorphous Fluorinated Acrylate Polymer Dielectrics for Flexible Transistors and Logic Gates with High Operational Stability.

Fluorinated amorphous polymeric gate-insulating materials for organic thin-film transistors (OTFTs) not only form hydrophobic surfaces but also significantly reduce traps at the interface between the organic semiconductor and gate insulator. Therefore, these polymeric materials can enhance the OTFT's operation stability. In this study, we synthesized a new polymeric insulating material series composed of acrylate and fluorinated functional groups (with different ratios) named MBHCa-F and used them as gate insulators for OTFTs and in other applications. The insulating features of the MBHCa-F polymers, including surface energy, surface atomic content properties, dielectric constant, and leakage current, were clearly analyzed with respect to the content of the fluorinated functional groups. At higher fluorine-based functional group content, the polymeric series exhibited higher fluorine-based contents at the surface and superior electrical properties, such as field-effect mobility and driving stability, at OTFTs. Therefore, we believe that this study provides a substantial method for synthesizing polymeric insulating materials to enhance the operational stability and electrical performance of OTFTs.

Sustainable removal of nitrite waste to value-added ammonia on Cu@Cu2O core-shell nanostructures by pulsed laser technique.

The biochemical reduction of nitrite (NO2-) ions to ammonia (NH3) requires six electrons and is catalyzed by the cytochrome c NO2- reductase enzyme. This biological reaction inspired scientists to explore the reduction of nitrogen oxyanions, such as nitrate (NO3-) and NO2- in wastewater, to produce the more valuable NH3 product. It is widely known that copper (Cu)-based nanoparticles (NPs) are selective for the NO3- reduction reaction (NO3-RR), but the NO2-RR has not been well explored. Therefore, we attempted to address the electrocatalytic conversion of NO2- to NH3 using Cu@Cu2O core-shell NPs to simultaneously treat wastewater by removing NO2- and producing valuable NH3. The Cu@Cu2O core-shell NPs were constructed using the pulsed laser ablation of Cu sheet metal in water. The core-shell nanostructure of these particles was confirmed by various characterization techniques. Subsequently, the removal of NO2- and the ammonium (NH4+)-N yield rate were estimated using the Griess and indophenol blue methods, respectively. Impressively, the Cu@Cu2O core-shell NPs exhibited outstanding NO2-RR activity, demonstrating a maximum NO2- removal efficiency of approximately 94% and a high NH4+-N yield rate of approximately 0.03 mmol h-1.cm-2 at -1.6 V vs. a silver/silver chloride reference electrode under optimal conditions. The proposed NO2-RR mechanism revealed that the (111) facet of Cu favors the selective conversion of NO2- to NH3 via a six-electron transfer. This investigation may offer a new insight for the rational design and detailed mechanistic understanding of electrocatalyst architecture for the effective conversion of NO2- to NH4+.

Electrohydrodynamic-Jet-Printed Phthalimide-Derived Conjugated Polymers for Organic Field-Effect Transistors and Logic Gates.

A π-conjugated polymer semiconductor, PBDTTTffPI, was synthesized for use as an organic semiconductor suitable for electrohydrodynamic (EHD) jet printing technology. Bulky alkylation of the polymer gave PBDTTTffPI good solubility in several organic solvents. EHD jet printing using PBDTTTffPI ink produced direct patterns of polymer semiconductors while maintaining smooth surface morphologies and crystal structures similar to those of spin-coated PBDTTTffPI films. EHD-jet-printed PBDTTTffPI was appropriate for use as a semiconductor layer in organic field-effect transistors (OFETs) and logic gates. OFETs that used EHD-jet-printed PBDTTTffPI had better electrical characteristics than devices that used spin-coated semiconductor films. When a dielectric material (Al2O3) with a high dielectric constant was introduced, the jet-printed PBDTTTffPI operated well at low voltages. Integrated devices such as inverters, NAND gates, and NOR gates were fabricated by printing PBDTTTffPI patterns and showed good switching behaviors. Therefore, the use of printable PBDTTTffPI provides an advance toward fabrication of practical integrated arrays in next-generation devices.

Influence of Material Properties on the Damage-Reporting and Self-Healing Performance of a Mechanically Active Dynamic Network Polymer in Coating Applications.

We conducted a detailed investigation of the influence of the material properties of dynamic polymer network coatings on their self-healing and damage-reporting performance. A series of reversible polyacrylate urethane networks containing the damage-reporting diarylbibenzofuranone unit were synthesized, and their material properties (e.g., indentation modulus, hardness modulus, and glass-transition temperature) were measured conducting nanoindentation and differential scanning calorimetry experiments. The damage-reporting and self-healing performances of the dynamic polymer network coatings exhibited opposite tendencies with respect to the material properties of the polymer network coatings. Soft polymer network coatings with low glass-transition temperature (~10 °C) and indentation hardness (20 MPa) exhibited better self-healing performance (almost 100%) but two times worse damage-reporting properties than hard polymer network coatings with high glass-transition temperature (35~50 °C) and indentation hardness (150~200 MPa). These features of the dynamic polymer network coatings are unique; they are not observed in elastomers, films, and hydrogels, whereby the polymer networks are bound to the substrate surface. Evidence indicates that controlling the polymer's physical properties is a key factor in designing high-performance self-healing and damage-reporting polymer coatings based on mechanophores.

Metal-Ion Chelating Gel Polymer Electrolyte for Ni-Rich Layered Cathode Materials at a High Voltage and an Elevated Temperature.

Nickel-rich layered oxides (LiNi1-x-yCoxMnyO2; (1 - x - y) ≥ 0.6), the high-energy-density cathode materials of lithium-ion batteries (LIBs), are seriously unstable at voltages higher than 4.5 V versus Li/Li+ and temperatures higher than 50 °C. Herein, we demonstrated that the failure mechanism of a nickel-rich layered oxide (LiNi0.6Co0.2Mn0.2O2) behind the instability was successfully suppressed by employing cyanoethyl poly(vinyl alcohol) having pyrrolidone moieties (Pyrd-PVA-CN) as a metal-ion-chelating gel polymer electrolyte (GPE). The metal-ion-chelating GPE blocked the plating of transition-metal ions dissolved from the cathode by capturing the ions (anode protection). High-concentration metal-ion environments developed around the cathode surface by the GPE suppressed the irreversible phase transition of the cathode material from the layered structure to the rock-salt structure (cathode protection). Resultantly, the capacity retention was significantly improved at a high voltage and a high temperature. Capacity retention and coulombic efficiency of a full-cell configuration of a nickel-rich layered oxide with graphite were significantly improved in the presence of the GPE especially at a high cutoff voltage (4.4 V) and an elevated temperature (55 °C).

Polymer-based flexible NOx sensors with ppb-level detection at room temperature using breath-figure molding.

A strategically designed polymer semiconductor thin film morphology with both high responsivity to the specific gas analyte and high signal transport efficiency is reported to realize high-performance flexible NOx gas sensors. Breath-figure (BF) molding of polymer semiconductors enables a finely defined degree of nano-porosity in polymer films with high reproducibility while maintaining high charge carrier mobility characteristics of organic field effect transistors (OFETs). The optimized BF-OFET with a donor-acceptor copolymer exhibits a maximum responsivity of over 104%, sensitivity of 774% ppm-1, and limit of detection (LOD) of 110 ppb against NO at room temperature. When tested across at NO concentrations of 0.2-10 ppm, the BF-OFET gas sensor exhibits a response time of 100-300 s, which is suitable for safety purposes in practical applications. Furthermore, BF-OFETs show a high reproducibility as confirmed by statistical analysis on 64 independently fabricated devices. The selectivity of NOx analytes is tested by comparing the sensing ability of BF-OFETs with those of other reducing gases and volatile organic compounds; the BF-OFET gas sensor platform monitors specific gas analytes based on their polarity and magnitude of sensitivity. Finally, flexible BF-OFETs conjugated with plastic substrates are demonstrated and they exhibit a sensitivity of 500% ppm-1 and a LOD of 215 ppb, with a responsivity degradation of only 14.2% after 10 000 bending cycles at 1% strain.

Synthesis and Characterization of Novel Triarylmethane-Based Dyes for Thermally Stable Blue Color Filters.

Two new triarylmethane-based dye molecules with a dimeric structure, TAM-1 and TAM-2, were designed and synthesized as potential blue color filter materials for liquid-crystal displays. The dimeric structure of TAM-1 was designed to improve the thermal stability of a well-known blue dye, Victoria Blue BO. TAM-2 was designed to further improve the solubility of TAM-1 by introducing long alkyl ester groups. The synthesized dyes TAM-1 and TAM-2 were transmissive in the wavelength range of 410-460 nm and showed good thermal stability with 5% weight degradation temperatures (T5d) of 259 °C and 289 °C, respectively, and less than 1% of weight loss at 230 °C. Moreover, TAM-2 showed excellent solubility (20.1 wt%) as opposed to Victoria Blue BO (0.03 wt%) and TAM-1 (3.5 wt%) in PGMEA.

A ball milling-based one-step transformation of chitin biomass to organo-dispersible strong nanofibers passing highly time and energy consuming processes.

Chitin, a sustainable and functional biological macromolecule, can be converted into chitin nanofibers (ChNFs), and are applicable as a mechanically reinforcing and bioactive filler for polymer matrices. Improving the performance of ChNFs typically relies on their nanofibrilization and miscibility with matrices. To transform chitin biomass into organo-dispersible ChNFs, a series of time-/energy-consuming chemical and mechanical treatments are required: 1) deacetylation, 2) disintegration, 3) surface modification to minimize their aggregation through hydrogen bonds, 4) drying, and 5) re-dispersion. This paper presents a one-step method to transform chitin biomass to organo-dispersible acetylated ChNFs via a ball-milling method in the presence of relatively low toxic acetic anhydride without water. This method minimizes water contaminations and energy for dehydrating. The resulting chitin nanofiber material is mixed with poly(l­lactic acid) (PLLA) to produce all-bio-based nanocomposites. The composite indicated a 66% increase in Young's modulus and a 100% increase in tensile strength compared to the pristine PLLA. Furthermore, it did not exhibit any observable cytotoxic effect, thus potentially applicable as a biomedical material.

Synthesis and Properties of Fluorinated Styrene Copolymers as Antibiofouling Coatings.

A series of polystyrene (PS) copolymers containing 2,3,4,5,6-pentafluorostyrene units with different monomer ratios were prepared for antifouling applications. PS, poly(styrene-co-pentafluorostyrene) (poly(S-co-FS)), and poly(pentafluorostyrene) (PFS) were synthesized by free-radical polymerization and characterized by 1H NMR, Fourier-transform infrared spectroscopy, and gel permeation chromatography. The surface energy of the polymer films decreased with increasing content of fluorinated styrene. Protein adsorption experiments were carried out on the synthesized polymer films using fluorescein isothiocyanate-labeled bovine serum albumin as a fluorescent protein. The photo-luminescence intensity of the protein-adsorbed polymer films decreased dramatically as the content of hydrophobic fluorinated styrene increased, suggesting that poly(S-co-FS) copolymers and PFS could be used as potential antibiofouling coatings.

High Dielectric Performances of Flexible and Transparent Cellulose Hybrid Films Controlled by Multidimensional Metal Nanostructures.

Various wearable electronic devices have been developed for extensive outdoor activities. The key metrics for these wearable devices are high touch sensitivity and good mechanical and thermal stability of the flexible touchscreen panels (TSPs). Their dielectric constants (k) are important for high touch sensitivities. Thus, studies on flexible and transparent cover layers that have high k with outstanding mechanical and thermal reliabilities are essential. Herein, an unconventional approach for forming flexible and transparent cellulose nanofiber (CNF) films is reported. These films are used to embed ultralong metal nanofibers that serve as nanofillers to increase k significantly (above 9.2 with high transmittance of 90%). Also, by controlling the dimensions and aspect ratios of these fillers, the effects of their nanostructures and contents on the optical and dielectric properties of the films have been studied. The length of the nanofibers can be controlled using a stretching method to break the highly aligned, ultralong nanofibers. These nanofiber-embedded, high-k films are mechanically and thermally stable, and they have better Young's modulus and tensile strength with lower thermal expansion than commercial transparent plastics. The demonstration of highly sensitive TSPs using high-k CNF film for smartphones suggests that this film has significant potential for next-generation, portable electronic devices.

Effect of solvent on detectivity of solution-processed polymer photodetectors.

We demonstrate a high-performance solution-processed polymer photodetector (PPD) whose detectivity (D*) exceeds 10(11) Jones over almost the entire range of visible light. PPDs processed from a chlorobenzene solution using 1,8-diiodooctane (DIO) as an additive exhibit large crystalline domains with long-range order, in contrast to the featureless morphology of PPDs processed with pure solvent. Moreover, PPDs processed with DIO exhibit higher charge carrier mobility, and thus high photoconductive gain without compromising long carrier lifetime. Consequently, a high-loading ratio of DIO (3%) yielded a PPD whose D* in the visible range was over threefold higher than that of PPD without DIO.

A new amorphous semiconducting polythiophene for high-performance organic thin-film transistors.

A new amorphous semiconducting polymer containing dodecylthiophene rings and a rigid thieno[3,2-b]thiophene ring, poly(2,5-bis(3'-dodecyl-2,2'-bithiophen-5-yl)thieno[3,2-b]thiophene) (NAP), was synthesized via a microwave-assisted Stille coupling reaction. The presence of the flexible unsubstituted thiophene ring units next to the rigid fused thiophene ring caused NAP to have an amorphous structure. This structure was confirmed by XRD, AFM, and computational calculations. In particular, the out-of-plane XRD patterns of NAP thin films exhibited no reflection peaks before or after the annealing process, indicating that the films had amorphous microstructures. In addition, AFM images of the NAP thin films showed amorphous surface morphologies with very small root-mean-square (rms) surface roughnesses of 0.3-0.5 nm, independent of surface treatment or heat treatment. Computational calculations performed to investigate the preferred conformation of the polymer confirmed the amorphous characteristics of the NAP structure. On the basis of these findings, we propose how an amorphous NAP semiconductor can maintain high carrier mobility. A NAP-based TFT device exhibited a very high carrier mobility of 0.02 cm(2) V(-1) s(-1) with an on/off ratio of 1 x 10(5) and a very small threshold voltage of -2.0 V. This carrier mobility is the highest yet reported for TFTs based on amorphous semiconductors. Thus, the present findings suggest that an amorphous semiconductor layer comprised of NAP would be suitable for use in high-performance organic TFTs fabricated via simple processes in which neither surface treatment nor heat treatment is necessary.

New anthracene-thiophene-based copolymers that absorb across the entire UV-vis spectrum for application in organic solar cells.

We report a new class of anthracene-thiophene-based copolymers, PAT4. The UV-vis absorption spectrum of PAT4 was broad and covered the full range of the solar spectrum. The hole mobility of PAT4 was high, up to 0.037 cm(2) V(-1) s(-1). PAT4-based organic solar cells showed promising power conversion efficiencies of 1.7%.

Synthesis and photovoltaic properties of cyclopentadithiophene-based low-bandgap copolymers that contain electron-withdrawing thiazole derivatives.

We have synthesized four types of cyclopentadithiophene (CDT)-based low-bandgap copolymers, poly[{4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2,6-diyl}-alt-(2,2'-bithiazole-5,5'-diyl)] (PehCDT-BT), poly[(4,4-dioctyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2,6-diyl)-alt-(2,2'-bithiazole-5,5'-diyl)] (PocCDT-BT), poly[{4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2,6-diyl}-alt-{2,5-di(thiophen-2-yl)thiazolo[5,4-d]thiazole-5,5'-diyl}] (PehCDT-TZ), and poly[(4,4-dioctyl-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2,6-diyl)-alt-{2,5-di(thiophen-2-yl)thiazolo[5,4-d]thiazole-5,5'-diyl}] (PocCDT-TZ), for use in photovoltaic applications. The intramolecular charge-transfer interaction between the electron-sufficient CDT unit and electron-deficient bithiazole (BT) or thiazolothiazole (TZ) units in the polymeric backbone induced a low bandgap and broad absorption that covered 300 nm to 700-800 nm. The optical bandgap was measured to be around 1.9 eV for PehCDT-BT and PocCDT-BT, and around 1.8 eV for PehCDT-TZ and PocCDT-TZ. Gel permeation chromatography showed that number-average molecular weights ranged from 8000 to 14,000 g mol(-1). Field-effect mobility measurements showed hole mobility of 10(-6)-10(-4) cm(2) V(-1) s(-1) for the copolymers. The film morphology of the bulk heterojunction mixtures with [6,6]phenyl-C(61)-butyric acid methyl ester (PCBM) was also examined by atomic force microscopy before and after heat treatment. When the polymers were blended with PCBM, PehCDT-TZ exhibited the best performance with an open circuit voltage of 0.69 V, short-circuit current of 7.14 mA cm(-2), and power conversion efficiency of 2.23 % under air mass (AM) 1.5 global (1.5 G) illumination conditions (100 mW cm(-2)).

Soluble and easily crystallized anthracene derivatives: precursors of solution-processable semiconducting molecules.

New soluble anthracene derivatives containing thiophene and phenylenevinylene derivatives were synthesized via well-known synthetic routes. TIPS derivatives were added at the 9,10-positions of anthracene for the solubility and crystallinity. Both of the molecules were found to be promising for high charge mobility and stable organic semiconductors. The soluble anthracene core (TIPSAnt) is a potential precursor for the synthesis of novel semiconducting materials.