Preparation of a Crosslinked Poly(imide-siloxane) for Application to Transistor Insulation.

Insulated gate bipolar transistor (IGBT) is an important power device for the conversion, control, and transmission of semiconductor power, and is used in various industrial fields. The IGBT module currently uses silicone gel as an insulating layer. Since higher power density and more severe temperature applications have become the trend according to the development of electronic device industry, insulating materials with improved heat resistance and insulation performances should be developed. In this study, we intended to synthesize a new insulating material with enhanced thermal stability and reduced thermal conductivity. Poly(imide-siloxane) (PIS) was prepared and crosslinked through a hydrosilylation reaction to obtain a semi-solid Crosslinked PIS. Thermal decomposition temperature, thermal conductivity, optical transparency, dielectric constant, and rheological property of the Crosslinked PIS were investigated and compared to those of a commercial silicone gel. The Crosslinked PIS showed high thermal stability and low thermal conductivity, along with other desirable properties, and so could be useful as an IGBT-insulating material.

Flexible and Transparent Electrode Based on Ag-Nanowire Embedded Colorless Poly(amide-imide).

Graphene oxide-cysteamine-silver nanoparticle (GCA)/silver nanowire (AgNW)/GCA/colorless poly(amide-imide) (cPAI) structures based on cPAI substrates with polyimide and polyamide syntheses were fabricated to study their characteristics. A layer of electrodes was constructed using a sandwich structure-such as GCA/AgNW/GCA-with cPAI used as a substrate to increase the heat resistance and improve their mechanical properties. Furthermore, to overcome the disadvantages of AgNWs-such as their high surface roughness and weak adhesion between the substrate and electrode layers-electrodes with embedded structures were fabricated using a peel-off process. Through bending, tapping, and durability tests, it was confirmed that these multilayer electrodes exhibited better mechanical durability than conventional AgNW electrodes. Resistive random-access memory based on GCA/AgNW/GCA/cPAI electrodes was fabricated, and its applicability to nonvolatile memory was confirmed. The memory device had an ON/OFF current ratio of ~104@0.5 V, exhibiting write-once-read-many time characteristics, maintaining these memory characteristics for up to 300 sweep cycles. These findings suggest that GCA/AgNW/GCA/cPAI electrodes could be used as flexible and transparent electrodes for next-generation flexible nonvolatile memories.

Repeatable Self-Healing of a Protective Coating Based on Vegetable-Oil-Loaded Microcapsules.

Generally, microcapsule-based self-healing materials have the limitation of single local self-healing. A few studies have reported repeatable self-healing in these microcapsular materials, but there is a challenge to develop multi-cycle self-healing materials that have the advantages of easier preparation and a more efficient operation. In this work, a mixture of two vegetable oils, soybean and olive oil, was used as a healing agent. The atmospheric oxygen-induced reaction behavior (in the presence of a catalyst) was investigated for various compositions of the vegetable oil mixtures; infrared spectroscopy, recovery testing, and viscoelasticity measurement were performed to find an optimum composition of the healing agent. Microcapsules loaded with soybean oil and catalyst-containing olive oil were separately prepared and used to prepare a dual-capsule self-healing coating. It was demonstrated through optical and scanning electron microscopy that, upon scribing the self-healing coating, the vegetable oils flowed out from microcapsules to self-heal the damaged area. When the healed area of the self-healing coating was re-scribed, self-healing was repeated, which was confirmed by scanning electron microscopy (SEM) and anticorrosion and electrochemical testing. Our new repeatable self-healing coating provides the merits of easy preparation, no need for external intervention such as light irradiation, and an environmentally-friendly nature.

Transparent Self-Cleaning Coatings Based on Colorless Polyimide/Silica Sol Nanocomposite.

We herein report transparent self-cleaning coatings based on polyimide-fluorinated silica sol (PIFSS) nanocomposite. Polyamic acid-silica sol (PASS) suspensions were synthesized by adding four different amounts of a silica sol suspension to each end-capped polyamic acid solution. The PASS suspensions were spin-coated on glass slides, thermally imidized and treated with triethoxy-1H,1H,2H,2H-perfluorodecylsilane (TEFDS) to prepare PIFSS coatings. The PIFSS coatings showed high resistance to separation from glass substrates and thermal stability. Furthermore, the PIFSS coatings on the glass substrate could be cleanly removed using polar aprotic solvents and repeated coating was possible. As the amount of silica sol particles in the PIFSS coating was increased, the hydrophobic contact angle increased. Among them, PIFSS-10 and PIFSS-15 coatings showed nearly superhydrophobic contact angles (144° and 148°, respectively) and good self-cleaning property. It was confirmed by SEM and AFM studies that their hydrophobic and self-cleaning properties are due to uniform particle distribution and relatively high surface roughness. PIFSS-10 coating showed a high transmittance value (88%) at 550 nm and good self-cleaning property, therefore suitable as a transparent self-cleaning coating. The advantages of the coating are that the fabrication process is simple, and the substrate is reusable. The PIFSS coating is expected to be applied in solar cell panels, windows, lenses and safety goggles.

Microcapsule-Type Self-Healing Protective Coating That Can Maintain Its Healed State upon Crack Expansion.

The purpose of this study was to develop a microcapsule-type self-healing coating system that could self-heal cracks and then maintain the healed state even upon crack expansion. Mixtures consisting of a photoinitiator and two methacrylate components, bismethacryloxypropyl-terminated polydimethylsiloxane (BMT-PDMS) and monomethacryloxypropyl-terminated PDMS (MMT-PDMS), were transformed into viscoelastic semi-solids through photoreaction. The viscoelasticity of the reacted mixtures could be controlled by varying the mass ratio of the two methacrylates. Through a stretchability test, the optimal composition mixture was chosen as a healing agent. Microcapsules loaded with the healing agent were prepared and dispersed in a commercial undercoating to obtain a self-healing coating formulation. The formulation was applied onto mortar specimens, and then cracks were generated in the coating by using a universal testing machine (UTM). Cracks with around a 150-µm mean width were generated and were allowed to self-heal under UV light. Then, the cracks were expanded up to 650 µm in width. By conducting a water sorptivity test at each expanded crack width, the self-healing efficiency and capability of maintaining the healed state were evaluated. The B-M-1.5-1-based coating showed a healing efficiency of 90% at a 150-µm crack width and maintained its healing efficiency (about 80%) up to a 350-µm crack width. This self-healing coating system is promising for the protection of structural materials that can undergo crack formation and expansion.

Flexible Transparent Electrode Characteristics of Graphene Oxide/Cysteamine/AgNP/AgNW Structure.

Graphene oxide (GO)-cysteamine-Ag nanoparticles (GCA)-silver nanowire (AgNW) fabricated by depositing GCA over sprayed AgNWs on PET films were proposed for transparent and flexible electrodes, and their optical, electrical, and mechanical properties were analyzed by energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, atomic force microscopy, scanning electron microscopy, transmission electron microscopy, current-voltage measurements, and bending test. GCA-AgNW electrodes show optical transmittance of >80% at 550 nm and exhibit a high figure-of-merit value of up to 116.13 in the samples with sheet resistances of 20-40 Ω/◻. It was observed that the detrimental oxidation of bare AgNWs over time was considerably decreased, and the mechanical robustness was improved. To apply the layer as an actual electrode in working devices, a Pt/GO/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate/GCA-AgNW/polyethylene terephthalate structure was fabricated, and resistive switching memory was demonstrated. On the basis of these results, we confirm that the proposed GCA-AgNW layer can be used as transparent and flexible electrode.

Polyimide-Based PolyHIPEs Prepared via Pickering High Internal Phase Emulsions.

Pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA) oligoimide particles and PMDA-ODA poly(amic acid) salt (PAAS) were synthesized and used as stabilizers to prepare oil-in-water Pickering high internal phase emulsions (HIPEs). The stability of the Pickering HIPEs was investigated by dispersion stability analysis. Polyimide-based polyHIPEs could be prepared through freeze-drying and subsequent thermal imidization of the Pickering HIPEs. The characteristics of the polyHIPEs, including their morphology, porosity, thermal decomposition temperature, and compression modulus, were investigated. The thermal decomposition temperature (T10) of the polyHIPEs was very high (>530 °C), and their porosity was as high as 92%. The polyimide-based polyHIPEs have the potential to be used in high-temperature environments.

Enhancement of the Mechanical Properties of Polyimide Film by Microwave Irradiation.

Polyimide films have conventionally been prepared by thermal imidization of poly(amic acid)s (PAAs). Here we report that the improvement of tensile strength while increasing (or maintaining) film flexibility of polyimide films was accomplished by simple microwave (MW) irradiation of the PAAs. This improvement in mechanical properties can be attributed to the increase in molecular weight of the polyimides by MW irradiation. Our results show that the mechanical properties of polyimide films can be improved by MW irradiation, which is a green approach that requires relatively low MW power, very short irradiation time, and no incorporation of any additional inorganic substance.

Preparation of Polyimide/Graphene Oxide Nanocomposite and Its Application to Nonvolatile Resistive Memory Device.

2,6-Diaminoanthracene (AnDA)-functionalized graphene oxide (GO) (AnDA-GO) was prepared and used to synthesize a graphene oxide-based polyimide (PI-GO) by the in-situ polymerization method. A PI-GO nanocomposite thin film was prepared and characterized by infrared (IR) spectroscopy, thermogravimetric analysis (TGA) and UV-visible spectroscopy. The PI-GO film was used as a memory layer in the fabrication of a resistive random access memory (RRAM) device with aluminum (Al) top and indium tin oxide (ITO) bottom electrodes. The device showed write-once-read-many-times (WORM) characteristics with a high ON/OFF current ratio (Ion/Ioff = 3.41 × 108). This excellent current ratio was attributed to the high charge trapping ability of GO. In addition, the device had good endurance until the 100th cycle. These results suggest that PI-GO is an attractive candidate for applications in next generation nonvolatile memory.

An Oligoimide Particle as a Pickering Emulsion Stabilizer.

A pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA)-based oligoimide (PMDA-ODA) was synthesized by a one-step procedure using water as a solvent. The PMDA-ODA particles showed excellent partial wetting properties and were stably dispersed in both water and oil phases. A stable dispersion was not obtained with comparison PMDA-ODA particles that were synthesized by a conventional two-step method using an organic solvent. Both oil-in-water and water-in-oil Pickering emulsions were prepared using the oligoimide particles synthesized in water, and the size of the emulsion droplet was controlled based on the oligoimide particle concentration. The oligoimide particles were tested to prepare Pickering emulsions using various kinds of oils. The oil-in-water Pickering emulsions were successfully applied to prepare microcapsules of the emulsion droplets. Our new Pickering emulsion stabilizer has the advantages of easy synthesis, no need for surface modification, and the capability of stabilizing both oil-in-water and water-in-oil emulsions.

Low-Temperature Self-Healing of a Microcapsule-Type Protective Coating.

Low-temperature self-healing capabilities are essential for self-healing materials exposed to cold environments. Although low-temperature self-healing concepts have been proposed, there has been no report of a microcapsule-type low-temperature self-healing system wherein the healing ability was demonstrated at low temperature. In this work, low-temperature self-healing of a microcapsule-type protective coating was demonstrated. This system employed silanol-terminated polydimethylsiloxane (STP) as a healing agent and dibutyltin dilaurate (DD) as a catalyst. STP underwent a condensation reaction at -20 °C in the presence of DD to give a viscoelastic product. The reaction behavior of STP and the viscoelasticity of the reaction product were investigated. STP and DD were separately microencapsulated by in situ polymerization and interfacial polymerization methods, respectively. The STP- and DD-loaded microcapsules were mixed into a commercial enamel paint, and the resulting formulation was applied to glass slides, steel panels, and mortars to prepare self-healing coatings. When the self-healing coatings were damaged at a low temperature (-20 °C), STP and DD were released from broken microcapsules and filled the damaged area. This process was effectively visualized using a fluorescent dye. The self-healing coatings were scratched and subjected to corrosion tests, electrochemical tests, and saline solution permeability tests. The temperature of the self-healing coatings was maintained at -20 °C before and after scratching and during the tests. We successfully demonstrated that the STP/DD-based coating system has good low-temperature self-healing capability.

Microcapsule-Type Self-Healing Protective Coating for Cementitious Composites with Secondary Crack Preventing Ability.

A microcapsule-type self-healing protective coating with secondary crack preventing capability has been developed using a silanol-terminated polydimethylsiloxane (STP)/dibutyltin dilaurate (DD) healing agent. STP undergoes condensation reaction in the presence of DD to give a viscoelastic substance. STP- and DD-containing microcapsules were prepared by in-situ polymerization and interfacial polymerization methods, respectively. The microcapsules were characterized by Fourier-transform infrared (FT-IR) spectroscopy, optical microscopy, and scanning electron microscopy (SEM). The microcapsules were integrated into commercial enamel paint or epoxy coating formulations, which were applied on silicon wafers, steel panels, and mortar specimens to make dual-capsule self-healing protective coatings. When the STP/DD-based coating was scratched, self-healing of the damaged region occurred, which was demonstrated by SEM, electrochemical test, and water permeability test. It was also confirmed that secondary crack did not occur in the healed region upon application of vigorous vibration to the self-healing coating.

Metabolic Suppression by 3-Iodothyronamine Induced Muscle Cell Atrophy via Activation of FoxO-Proteasome Signaling and Downregulation of Akt1-S6K Signaling.

The homeostasis of muscle properties depends on both physical and metabolic stresses. Whereas physical stress entails metabolic response for muscle homeostasis, the latter does not necessarily involve the former and may thus solely affect the homeostasis. We here report that metabolic suppression by the hypometabolic agent 3-iodothyronamine (T1AM) induced muscle cell atrophy without physical stress. We observed that the oxygen consumption rate of C2C12 myotubes decreased 40% upon treatment with 75 µM T1AM for 6 h versus 10% in the vehicle (dimethyl sulfoxide) control. The T1AM treatment reduced cell diameter of myotubes by 15% compared to the control (p<0.05). The cell diameter was reversed completely by 9 h after T1AM was removed. The T1AM treatment also significantly suppressed the expression levels of heat shock protein 72 and αB-crystallin as well as the phosphorylation levels of Akt1, mammalian target of rapamycin (mTOR), S6K, forkhead box O1 (FoxO1) and FoxO3. In contrast, the levels of ubiquitin E3 ligase MuRF1 and chymotrypsin-like activity of proteasome were significantly elevated by T1AM treatment. These results suggest that T1AM-mediated metabolic suppression induced muscle cell atrophy via activation of catabolic signaling and inhibition of anabolic signaling.

Behavioral hypothermia of a domesticated lizard under treatment of the hypometabolic agent 3-iodothyronamine.

Ectothermic animals rely on behavioral thermoregulation due to low capacity of heat production and storage. Previously, lizards were shown to achieve 'fever' during microbial infection by increasing their preferred body temperature (PBT) behaviorally, thereby attaining a relatively high survival rate. The purpose of this study was to investigate whether domesticated lizards pursued 'behavioral hypothermia' induced by a hypometabolic agent 3-iodothyronamine (T1AM). We found that treatment with 8.0 mg/kg T1AM caused a lizard species, the leopard gecko (Eublepharis macularius), to decrease its ventilation and oxygen consumption rates 0.64- and 0.76-fold, respectively, compared to those of the control (P<0.05). The lizards, habituated at an ambient temperature of 30 ± 0.5°C, also showed a significant decrease in the PBT range over a freely accessible thermal gradient between 5°C and 45°C. The upper limit of the PBT in the treated lizards lowered from 31.9°C to 30.6°C, and the lower limit from 29.5°C to 26.3°C (P<0.001). These findings demonstrate that the treated lizards pursued behavioral hypothermia in conjunction with hypoventilation and hypometabolism. Because prior studies reported a similar hypometabolic response in T1AM-injected laboratory mice, the domesticated lizards, as a part of the vertebrate phylogeny, may be a useful laboratory model for biological and pharmacological researches such as drug potency test.

Microcapsule-Type Organogel-Based Self-Healing System Having Secondary Damage Preventing Capability.

We have developed a novel microcapsule-type organogel-based self-healing system in which secondary damage does not occur in the healed region. A mixture of an organogelator, poor and good solvents for the gelator is used as the healing agent; when the good solvent evaporates from this agent, a viscoelastic organogel forms. The healing agent is microencapsulated with urea-formaldehyde polymer, and the resultant microcapsules are integrated into a polymer coating to prepare self-healing coatings. When the coatings are scratched, they self-heal, as demonstrated by means of corrosion testing, electrochemical testing, optical microscopy, and scanning electron microscopy (SEM). After the healed coatings are subjected to vigorous vibration, it is demonstrated that no secondary damage occurs in the healed region. The secondary damage preventing capability of the self-healing coating is attributable to the viscoelasticity of the organogel. The result can give insight into the development of a "permanent" self-healing system.

Characteristics and Durability of Vertical-Type Organic Light-Emitting Transistors Using Poly(2-methoxy-5-(2- ethyl hexyloxy)-1,4-phenylenevinylene) and Indenofluorenedione Derivatives.

In this study, we have fabricated vertical organic light emitting transistors using indenofluorenedione derivatives (IF-dione-F) as an n-type organic semiconductor. IF-dione-F shows high performance n-type semiconductors owing to the fluorine group in the IF-dione-F backbone. The fluorine group has an electron-withdrawing property. Thus, IF-dione-F shows high electron affinity and good durability. The configuration of the vertical organic light emitting transistors was ITO (drain)/ PEDOT: PSS/MEH-PPV/IF-dione-F/AI (gate)/IF-dione-F/Al (source). The characteristics of the vertical organic light emitting transistors were investigated from the measurements of radiancevoltage characteristics and external quantum efficiency. Furthermore, air stability was studied from the measurements of characteristics, impedance spectroscopy and contact angle.

Green synthesis and biological evaluation of new di-α-aminophosphonate derivatives as cytotoxic agents.

A series of novel di-α-aminophosphonate derivatives were synthesized by a one-pot method in the presence of PEG-H2 O under ultrasonic irradiation and were characterized by IR, (1) H NMR, (13) C NMR, mass spectrometry, and elemental analysis. The newly synthesized compounds were evaluated for their cytotoxic activities against the human lung cancer cell line H1299 and the human breast cancer cell line MCF7 in vitro by the MTT method. All compounds showed moderate cytotoxic activity on both cell lines, and compounds 4b and 4c showed marked activity.

Sunlight-induced self-healing of a microcapsule-type protective coating.

Photopolymerization behavior of a methacryloxypropyl-terminated polydimethylsiloxane (MAT-PDMS) healing agent was investigated in the presence of benzoin isobutyl ether (BIE) photoinitiator by Fourier transform infrared (FT-IR) spectroscopy. MAT-PDMS and BIE were microencapsulated with urea-formaldehyde polymer. The surface and shell morphology of the microcapsules was investigated by scanning electron microscopy (SEM). Mean diameter and size distribution of the microcapsules could be controlled by agitation rate. A coating matrix formulation was prepared by sol-gel reaction of tetraethyl orthosilicate (TEOS) in the presence of a polysiloxane and by subsequent addition of an adhesion promoter. The formulation and microcapsules were mixed to give a self-healing coating formulation, which was then sprayed to surface of cellulose-fiber-reinforced-cement (CRC) board or mortar. Contact angle measurements showed that both the polymerized MAT-PDMS and the prepared coating matrix are hydrophobic, and the coating matrix has good wettability with MAT-PDMS. It was confirmed by optical microscopy and SEM that, when the self-healing coating is damaged, the healing agent is released from ruptured microcapsules and fills the damaged region. The self-healing coating was evaluated as protective coating for mortar, and it was demonstrated by water permeability and chloride ion penetration tests that our system has sunlight-induced self-healing capability. Our self-healing coating is the first example of capsule-type photoinduced self-healing system, and offers the advantages of catalyst-free, environmentally friendly, inexpensive, practical healing.

In vivo molecular imaging of [125I]-labeled 3-iodothyronamine: a hibernation-inducing agent.

The present investigation was carried out with the objective of studying in vivo imaging of 3-iodothyronamine (T(1)AM) compound in mice. A simple and efficient synthesis of [(125)I]-T(1)AM was established, and a molecular imaging study was performed using micro-SPECT/CT at 1h post-injection of [(125)I]-T(1)AM. Imaging studies revealed the activity in the gastrointestinal tract and liver, indicating that [(125)I]-T(1)AM was distributed primarily in the liver, and excreted into the gastrointestinal tract through a bile duct.

All solution processable organic photovoltaic cells using DMDCNQI as an organic N-type buffer layer.

Organic photovoltaic cells consisting of ITO/PEDOT-PSS/P3HT:PCBM/TiO(x)/DMDCNQI/Al have been fabricated by using dip-coated DMDCNQI layer as a cathode buffer material. We have investigated the physical effects of charge transfer complex and wettability of DMDCNQI between TiO(x)/P3HT:PCBM layer and Al cathode electrode on the performance of organic photovoltaic cell. The photovoltaic cell fabricated with a dip-coated DMDCNQI layer exhibited almost similar performance compared to the device using conventional evaporated DMDCNQI layer. Especially, the power conversion efficiency of the prepared organic photovoltaic cell using TiO(x)/DMDCNQI layer was improved to 3.1%, which is mainly due to the decrease in the low contact resistance of organic-metal interface.