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Molten carbonate fuel cells (MCFCs) are environmentally friendly, large-capacity power generation devices operated at approximately 650°C. If MCFCs are to be commercialized by improving their competitiveness, their cell life should be increased by operating them at lower temperatures. However, a decrease in the operating temperature causes a reduction in the cell performance because of the reduction in the electrochemical reaction rate. The cell performance can be improved by introducing a coating on the cathode of the cell. A coating with a high surface area expands the triple phase boundaries (TPBs) where the gas and electrolyte meet on the electrode surface. And the expansion of TPBs enhances the oxygen reduction reaction of the cathode. Therefore, the cell performance can be improved by increasing the reaction area, which can be achieved by coating nanosized LiCoO2 particles on the cathode. However, although a coating improves the cell performance, a thick coating makes gas difficult to diffuse into the pore of the coating and thus reduces the cell performance. In addition, LiCoO2-coated cathode cell exhibits stable cell performance because the coating layer maintains a uniform thickness under MCFC operating conditions. Therefore, the performance and stability of MCFCs can be improved by applying a LiCoO2 coating with an appropriate thickness on the cathode.

Polymeric coating materials (PCMs) are promising candidates for developing next-generation flexible displays. However, PCMs are frequently subjected to external stimuli, making them highly susceptible to repeated damage. Therefore, in this study, a highly self-healing PCM based on a charge transfer complex (CTC) was developed, and its thermal, self-healing, and mechanical properties were examined. The self-healing material demonstrated improved thermal stability, fast self-healing kinetics (1 min), and a high self-healing efficiency (98.1%) via CTC-induced multiple interactions between the polymeric chains. In addition, it eliminated the trade-off between the mechanical strength and self-healing capability that is experienced by typical self-healing materials. The developed PCM achieved excellent self-healing and superior bulk (in-plane) and surface (out-of-plane) mechanical strengths compared to those of conventional engineering plastics such as polyether ether ketone (PEEK), polysulfone (PSU), and polyethersulfone (PES). These remarkable properties are attributed to the unique intermolecular structure resulting from strong CTC interactions. A mechanism for the improved self-healing and mechanical properties was also proposed by comparing the CTC-based self-healing PCMs with a non-CTC-based PCM.

The formic acid (CH

We investigated the effects of hydrogen separation using high-temperature anhydrous proton-exchange membrane fuel-cell technology. Various acid-doped para-polybenzimidazole (p-PBI)-chain end-tethered amine-polyhedral oligomeric silsesquioxane (NH2-POSS) membranes were prepared via a unique sol–gel transition method termed as the poly(phosphoric acid) process. The resulting NH2-POSS-capped p-PBI membranes exhibited a higher phosphoric acid-doping level (128–223.5%) and proton conductivity (0.23–0.29 S cm−1 at 160 °C and 0% relative humidity) than the parent p-PBI membrane. The chemical chain end-termination of p-PBI with cage-like NH2-POSS significantly enhanced the electrochemical H2/CO2 and H2/CO separation at 160 °C. The hydrogen separation of the NH2-POSS-capped p-PBI system required a relatively small amount of energy, and the system exhibited a good dynamic response. The favorable interfacial interaction between the NH2-POSS and the p-PBI host, high thermomechanical stability, and good fuel-cell and hydrogen-separation performance at high temperatures up to 160 °C indicate the applicability of the NH2-POSS-capped p-PBI membranes to electrochemical power generation and hydrogen pumps for practical industrial applications in harsh and extreme environments.

Fuel cells are cleaner alternatives of sustainable green energy sources. Their proton exchange membranes continue to be a key component; however, there are several challenges associated with their ...

Here, highly stretchable and transparent UV curable poly(urethane-acry-late) elastomer has been synthesized by reacting urethane acrylate oligomer and two reactive diluents monomers. The synthesized elastomers can be stretched up to 600% and have high transparency of over 90% transmittance. The synthesized elastomers have been applied to several applications. Simple 3D model was printed with a 3D printer on the market. Stretchable ionic conductors were fabricated by a facile method of adding salt with ionic conductivity. Similarly, the resin with β-cyclodextrin, a cage-structured molecule, was cured and foam was generated simultaneously under the UV radiation. This research paves a new way for further development in applications of UV curable transparent elastomer and 3D printable elastomeric material.

Polyimides, a widely used engineering plastic, require use of large amounts of toxic and hazardous organic solvents which threaten our daily lives, calling for new and easy synthetic methods for sustainable environmentally friendly development. In this paper, highly soluble fluorinated polyimides based on 4,4′-(hexafluoroisopropylidene) diphthalic anhydride were synthesized via hydrothermal process without using any toxic organic solvents and the advantages of the newly demonstrated synthetic methods are shown by comparative analysis performed with the two conventional synthetic methods using organic solvent: thermal and chemical imidization. Lower temperature is required (~200 °C) compared to thermal imidization and functional groups for high fusibility formed more easily compared to chemical imidization. According to the comparative analysis, hydrothermally synthesized PIs showed excellent solubility and maintained high thermal stability (&gt, 500 °C) and glass transition temperature (&gt, 300 °C) compared to conventional PI. The hydrothermally synthesized polyimide is much more convenient to store and manage than other form of polyimide which is much more stable when it is exposed to humidity as it is a powder form. The hydrothermal synthetic method is verified to be a “Green” and facile method for sustainable PI synthesis.

An inexpensive and general-purpose carbon fiber was prepared using coal tar pitch. In contrast to the solvent extraction process employing expensive solvents, a low-cost centrifugal separation method facilitated the reduction of loss due to the pitch purification and an overall yield increase. The coal tar pitch purified by centrifugation and subsequently co-carbonized with pyrolysis fuel oil improved in spinnability. Moreover, the resulting spinnable pitch had a softening point of 250 °C. The obtained carbon fibers were heat-treated at 1000 °C for 5 min, resulting in a tensile strength of approximately 1000 MPa and an average diameter of 9 μm. In this study, we present an effective method for obtaining low-cost general-purpose isotropic carbon fibers.

The main challenge to developing future display substrates is to synthesize flexible substrate materials that also have excellent optical and thermal properties, and low thermal expansion number. In this study, a novel trifluoromethylated asymmetric aromatic diamine, 4-[[4-(4-amino-2-trifluoromethylphenoxy)phenyl]sulfonyl-3-(trifluoromethyl)]benzenamine (AFPSFB), was synthesized through nucleophilic substitution. Conventional two-step polycondensation of AFPSFB with commercially available tetracarboxylic dianhydrides enabled the fabrication of fully or semi-aromatic polyimides (PIs). The resulting PIs were highly soluble in polar aprotic solvents with good optical and thermal properties. Next, polyhedral oligomeric silsesquioxane containing an amine group (NH2-POSS) was reacted with the resulting soluble PI. All the PI-POSS nanohybrids displayed excellent optical properties, including high transparency (>91% at 400 nm), low refractive index (

Polymer composite membrane technology is promising for enhancing the performance of membrane electrode assemblies for high-temperature fuel cells. In this study, we developed a novel anhydrous proton-exchange polybenzimidazole (m-PBI) composite membrane using Al-substituted mesoporous silica (Al-MCM-41) as a proton-carrier support. The surface-substituted Al-MCM-41 formed effective proton-transport pathways via its periodic hexagonal channel and improved the proton conductivity. The proton conductivity of an m-PBI filled with 9 wt.% filler was 0.356 S cm-1 at 160 °C and 0% humidity, representing an increase of 342% compared to that of a pristine m-PBI. Further, the current density at 0.6 V and maximum power density of m-PBI composite membranes were increased to 0.393 A cm-2 and 0.516 W cm-2, respectively. The enhanced fuel-cell performance was attributed to the proton-transfer channels and H3PO4 reservoirs formed by the mesopores of the Al-MCM-41 shell. The results indicated that Al-MCM-41 is suitable with respect to the hybrid homologues for enhancing the proton transport of the m-PBI membrane.

We report herein on thermally stable polyimide (PI) hybrid optical imaging sensors based on chalcogenide element-blocks that can be advantageously used in light-weight optical materials, especially in infrared (IR) applications. A change in the length of chalcogenide element-blocks, which formed the building block backbone of PI, induced a difference in overall transmittance in the visible and near IR range of frequencies. The PI hybrids covalently bonded with zirconia displayed tunable refractive indices up to 1.79 at 532 nm along with an unprecedented transmission from the visible to the IR spectral region. The amine-functionalized zirconia nanofillers can also significantly improve the thermomechanical properties of the host PI due to the favorable interaction with the PI matrix. In particular, we demonstrate that PI hybrids can accomplish high-quality IR thermographic imaging of human subjects, and even visualize details of elaborate micropatterns. Consequently, the PI hybrids can be used to manufacture thermally robust and transparent optical lenses that are cost-competitive compared to the conventionally used inorganic types, thus offering advantages of improved processability, flexibility, reduced volume, and light-weight characteristics.

Crosslinked metal oxide containing nanocomposite membranes, in which the filler also acts as crosslinker, were prepared by blending polybenzimidazole (PBI-OO) and phenylsulfonated TiO2 particles (s-TiO2). Thermal curing changes the ionically crosslinked system into a covalently crosslinked system. The synthesized s-TiO2 nanoparticles were analyzed by thermal gravimetric analysis and scanning electron microscopy. The covalently crosslinked nanocomposite membranes (c-sTiO2-PBI-OO) were doped with phosphoric acid (PA) for high temperature proton exchange membrane fuel cell (HT-PEMFC) application. The membrane properties, such as PA uptake, dimensional change, gel content, proton conductivity, mechanical property, and single cell performance were evaluated and compared with the properties of acid-doped c-PBI-OO. PA doped 6-c-sTiO2-PBI-OO (6 wt% sTiO2) showed the highest uptake of 392 wt%, and a proton conductivity at 160 °C of 98 mS cm−1. In the fuel cell, a peak power density of 356 mW cm−2 was obtained, which is 76% higher than that of a c-PBI-OO based system (202 mW cm−2). To evaluate the stability of the membrane performance over time, the best performing membrane was tested for over 700 h.

A method to improve the optical properties of transparent poly(amide-imide) (PAI) by incorporating a new flexible diamine is demonstrated. The new diamine-incorporated PAI films show a lower glass transition temperature, yellow index, residual stress than neat PAIs irrespective of their structure. The DSC results show that the new diamine increases the flexibility of the polymer matrix indicating the poor packing of the matrix. However, the light transmittance reduces from 89.73 to 88.58%. This discrepancy can be clarified by measuring the residual stress of the PAI films. The results confirm that PAI has high elasticity and flexibility at low and high temperatures. Thus, flexible diamines can be added to PAI films for transparent materials owing to their good optical properties such as a transmittance of over 87%, yellow index lower than 2.8 and low residual stress

A new diamine was designed and synthesized to improve the flexibility of colorless polyimides by reducing residual stress. Four variations of colorless polyimides with the same dianhydride (4,4′-(hexafluoroisopropylidene)-diphthalic) and four different diamines (bis[4-(3-aminophenoxy)-phenyl] sulfone, bis(3-aminophenyl) sulfone, 2,2′-bis(trifluoromethyl)benzidine, and 2,2-bis(4-aminophenyl)-hexafluoropropane) were used. A series of colorless polyimides were prepared by adding the new diamine. The carbon and ether bonds between the benzene rings of the new diamine affected the flexibility and optical properties of colorless polyimide. The synthesis of the new diamine was confirmed by NMR measurements. Furthermore, the decrease in residual stress at room temperature and the glass transition temperature was confirmed. The effect of the new diamine was most evident for polyimide with a bulky and rigid structure. Though a slight yellow color appears because of the broken charge transfer complex balance, controlling the content of the new diamine will allow application of polyimides in flexible display.

Nanocomposite polymer electrolyte membranes comprising a crosslinked polymer blend of poly(vinyl alcohol)/poly(styrene sulfonic acid-co-maleic acid) (PVA/PSSA-co-MA) and fumed silica nanoparticles were prepared for direct methanol fuel cell (DMFC) applications. Silica nanoparticles could be incorporated well uniformly in the completely miscible system, which can form a three-dimensional network structure to achieve the enhancement of mechanical properties as well as the additional reduction of methanol permeability. The optimized proton conductivities and methanol permeability of the PVA/PSSA-co-MA membrane with silica nanoparticles of 10 wt.% were 0.0482 S cm-1 at room temperature and 5.78 × 10-7 cm2 s-1 at the methanol concentration of 40% (w/w), respectively.

Due to rise in demand for mobile devices, development of complex stacked packaging technology such as multi-chip package, capable of both small size and high volume, are in high interest. As residual stress of individual chips increases, the degree of bending rises leading to more difficulty in package assembly process and decreased reliability of the final package product. To overcome this, deeper understanding of the thermal history and thermal behavior between the polymer film and substrates are needed. In this work, residual stress-temperature profiles of thermally stable polyimide/organically-modified layered silicate (PI/OLS) nanocomposite systems on Si wafer were investigated in situ during imidization and cooling process. This study provides systematic approach from the perspective of substrate design for multi-stacked semiconductor package.

When a large fuel cell power plant is connected to a district heating network, the cogeneration efficiency of the power plant is usually insufficient (60–79%). In this study, we focused on the latent heat of water generated from the fuel cell reaction H2 + O2 → H2O, which is an unutilized energy source. This technique is a potential solution for enhancing the total efficiency of the system. A new system linking a large-scale fuel cell power plant to a district heating system was developed. Its primary energy efficiency significantly increased (26.6%) owing to the maximum utilization of the latent heat from the water vapor condensation. This innovative system was installed in a 10.56 MW fuel-cell power plant, and operational data for the temperature and flow rate balance were obtained and analyzed. The results indicate that this system reduces investment costs by approximately 50% using cascade heat utilization technology for district heating systems, and consequently, the estimated payback period is less than 2 y.

Colorless polyimides (CPIs) with outstanding mechanical properties are used as essential materials in the production of future flexible display panels, foldable windows, and spacecraft cockpit materials. However, under repetitive stress and deformation, fatigue fractures caused by cracks and radio waves may act as critical determinants of the properties and duration of the material. To solve this problem, the present study developed a CPI capable of self-healing, wherein the transparency and any damage caused by external stress are rapidly and easily restored. Our synthesized CPI films showed ultra-transmittance (> 95%) and excellent self-healing efficiency (> 98%) with a simultaneously induced multi exchange network. Notably, the films exhibited excellent mechanical properties even after a bending fatigue test involving more than 10,000 cycles. This study therefore suggests a new type of CPI with a self-healing function and shows that the trade-off between the durability and functionality can be completely resolved.

The development of tannic‐acid‐based textile materials is a good candidate that enables both flame retardancy and antibacterial properties. When nanocarbon materials are used together, it is possible to not only realize complex functions but also increase physical properties, thereby expanding the potential range of application of the materials.

Traditionally, electromagnetic interference (EMI) shielding material has been occupied by metallic materials due to its high electric conductivity and EMI shielding effect. However, with rising demands from technology development for light-weight, highly durable, and easily moldable materials, metallic materials are gradually being substituted by polymer composite materials. Still, there are limitations on polymer composite as EMI shields: High ratio of fillers in composite achieves excellent EMI shielding effect but it severely compromises its mechanical behaviors. In many studies, they have failed to fabricate the high-ratio filler films with good mechanical durability, but here the initially fragile high-ratio film has been transformed to a flexible film by a very simple method: Hot-pressing. This approach not only solved the problems mentioned above but further provided a possible breakthrough point for composite study by solving threshold of the maximum loading of the fillers in polymer matrix. The stiff composite of polyimide sponge with exceeding carbon black loading became a highly flexible EMI SE film with doubled tensile strength and enhanced EMI SE. As a result, a new way of fabricating flexible EMI shielding polymer composite is demonstrated with great potential applications in aerospace and wireless communications.

Direct spinning of carbon nanotube (CNT) fibers is a facile method to produce CNT fibers because of its high productivity and the simplicity of the spinning process from CNT aerogels. Directly spun CNT fibers, however, generally include amorphous carbon and weak shear interaction between tubes or bundles, thereby causing insufficient load transfer. Here, we report newly designed polyimide/reduced graphene oxide (PI/RGO)/CNT fiber composites in combination with polymer infiltration followed by photonic flash sintering on a time scale of 0.5 ms to overcome the critical drawbacks in directly spun CNT fibers. The mechanical performances of the CNT fibers were closely related to the junction strength in CNT bundles. In addition, PI can be interlocked with CNT bundles and effectively serve as a binder to link the GO and CNT fibers with strong interfacial interactions. The PI infiltrated CNT fibers showed the highest load transfer, resulting in a significantly enhanced increase of 83% in specific strength (1.1 N/tex) and a 477% increase in tensile strength (800 MPa) compared to pristine CNT fibers. Furthermore, the photonic sintered PI/RGO/CNT fibers improved electrical conductivity by over 244% (5.5 × 103 S cm−1) over pristine CNT fibers without deteriorating mechanical properties. The results demonstrate that the mechanical strength, modulus and electrical conductivity can be enhanced simultaneously by molecular-level coupling of polymer/graphene with CNT fibers via photonic flash sintering.

In this study, transparent thin films for coating material are synthesized by adding bulky CF3 and hydroxyl groups intro into poly(amide-imide)s. As expected, these poly(amide-imide)s show higher shear adhesion and higher glass transition temperatures than the neat poly(amide-imide) due to hydrogen bonding of the hydroxyl groups. In addition, the modification to the poly(amide-imide) structure leads to only slight decreases in transmittance and yellow index. Consequently, the successful synthesis of poly(amide-imide)s with wide applications as transparent coating materials due to their optical properties and high adhesion is demonstrated. Transparent flexible display and coating products can be manufactured with poly(amide-imide)s having high reliability and a low chance of cracking due to their favorable thermal properties.

A transparent poly(amide-imide) (PAI) was synthesized with good thermal and optical properties and after that silica nano particles were introduced and removed for nano porous polymer matrix. The successful synthesis of PAI with nano scale porous structure was confirmed with FT-IR and FE-SEM measurement. The effects of free volume of polymer on thermal properties were measured with TGA and DSC. This physically modified polymer matrix showed increased thermal degradation and glass transition temperature over 250 °C. In the case of optical properties, UV-Vis and yellow index were measured and PAI with nano porous structure showed transparent colorless properties with light transmittance in the range of 80-40% and yellow index 2.1-1.1. The results also showed low dielectric constant in the range of 3.2-2.5 and contact angles that of 70-73°.

We report a facile method to enhance mechanical properties of polymer nanocomposites using three-dimensional (3D) network structures of functionalized graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs) in a polymer matrix. The GO and MWCNTs were functionalized using Fisher indole and diazonium-salt reactions to produce pyridine (Py) moiety on the GO and MWCNTs. The functionalized GO (Py-RGO) and MWCNT (Py-MWCNT) nanocomposites exhibited hydrogen-bond assisted 3D network structures in a polyimide (PI) matrix. By incorporating 1 wt% of carbon materials (0.9 wt% Py-RGO and 0.1 wt% Py-MWCNTs) in a PI, the tensile strength and modulus of the ternary nanocomposites reached 581 MPa and 31 GPa, respectively, which was an enhancement of 221% and 312% compared with pristine PI. The fracture energy of the PI/Py-RGO/Py-MWCNT nanocomposites improved 200% and approached 29.7 MJ m−3. The formation of the 3D network structure of the functionalized carbon nanomaterials is considered to significantly affect load transfer of nanofillers in the polymer matrix, and produce high performance polymer nanocomposites.

In this study, the improvement of synthesizing method of sponge-type polyimide (PI) membrane and its newly developed pore size control techniques are mainly described. The sponge-type polyimide membrane with large pore size (0.1–10 µm) and high permeability was successfully synthesized by using non-solvent phase separation method (NIPS) in continuous process and its full polyimidization is confirmed via Fourier-transform infrared technique. The theoretical approach in this research induced by Jurin's law which describes the height of a liquid within a thin capillary tube. In this theory, the pore size of membrane is highly influenced by the interactive tension between the polymer and solvents during synthesizing process of polymer membrane. There are two ways of controlling pore size established from Jurin's law. The validity of the application of Jurin's law was proven via comparison with theoretical and experimental data. Its inner structure of membrane and pore size are identified by field emission-scanning electron microscopy.

The need for flexible electronics with outstanding bending properties is increasing due to the demand for wearable devices and next-generation flexible or rollable smartphones. In addition, the requirements for flexible or rigid–flexible electronics are sharply increasing to achieve the design of space-saving electronic devices. In this regard, coverlay (CL) film is a key material used in the bending area of flexible electronics, albeit infrequently. Because flexible electronics undergo folding and unfolding numerous times, CL films with superior mechanical and bending properties are required so that the bending area can endure such severe stress. However, because current CL films are only used for a designated bending area in the flexible electronics panel, their highly complicated and expensive manufacturing procedure is a disadvantage. In addition, the thickness of CL films must be decreased to satisfy the ongoing requirement for increasingly thin products. However, due to the limitations of the two-layer structure of existing CL films, the manufacturing process cannot be made more cost effective by simply applying more thin film onto the board. To address this problem, we have developed liquid coverlay inks (LCIs) with superior bendable properties, in comparison with CL films, when applied onto flexible electronics using a screen-printing method. The results show that LCIs have the potential to become one of the leading candidates to replace existing CL films because of their lower cost and faster manufacturing process.

The decomposition of formic acid (HCOOH) over ZrO2 catalysts synthesized by precipitation method was investigated and their catalytic activity based on unit mass of catalyst was compared by varying the calcination temperature in the 500–1000 °C range. The calcined ZrO2 samples were characterized using temperature-programed desorption (TPD) of iso-propanol (IPA), H2O, and HCOOH as well as X-ray diffraction (XRD), pyridine-adsorbed infrared spectroscopy (Py-IR) and N2 sorption. The catalytic activity as a function of the calcination temperature of ZrO2 showed a volcano-type curve with a maximum at 900 °C. The catalytic activity of ZrO2 in the decomposition of HCOOH well correlated with Bronsted acid site density, and it was influenced by the crystalline phase of ZrO2. Furthermore, the evolution of the Bronsted acid site density measured by Py-IR as a function of the calcination temperature was in good accordance with the desorption temperature determined by IPA- and HCOOH-TPD experiments. When H2O vapor was added, the conversion of HCOOH slightly decreased, while the CO selectivity remained almost constant. However, when CO was supplied, the conversion of HCOOH decreased continuously, and the selectivity to H2 gradually increased, indicating that the formation of zirconium suboxides with characteristics approaching those of metals was successful using CO as a reductant.

Molten-carbonate fuel cells (MCFCs) are high-temperature fuel cell systems that typically operate at approximately 650 °C. Due to their high operating temperature, the thermal degradation of MCFC components limits the lifetime of the MCFC. Therefore, lowering the operating temperature is an effective way to reduce thermal degradation. However, the electrochemical reaction on the cathode also becomes slower as the operational temperature decreases. To improve the performance and stability, atomic layer deposition (ALD) of ZrO2 on the cathode is proposed. ALD produces a uniform, thin coating with precise thickness control. Therefore, nano-coating can be performed via ALD without affecting the porous structure of the cathode. The uniform ZrO2 coating donates electrons to NiO due to the low electronegativity of Zr. The electron-rich environment of NiO improves the cell performance by providing electrons for the oxygen reduction reaction. Also, the single cell using ZrO2-coated cathode demonstrates improved stability compared to the uncoated cathode cell due to the inhibition of NiO sintering by the ZrO2 coating layer.

New diamines for high-performance poly(ester imide)s (PEsIs) containing dimethyl groups at the ortho-position of amino groups and ester derivatives have been developed to improve optical transparency and glass transition temperature (Tg) while maintaining a low coefficient of thermal expansion (CTE). Four kinds of PEsIs derived from bis(4-amino-3,5-dimethylphenyl) terephthalate (BADMT) and aromatic dianhydrides such as 1,2,4,5-benzenetetracarboxylic dianhydride (PMDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 4,4’-oxydiphthalic anhydride (ODPA), and 4,4'-(hexafluoroisopropylidene)diphthalic (6FDA) were synthesized via a two-step polycondensation. All PEsIs exhibited outstanding properties, such as light color, a good transmittance of >90% at 550 nm, high Tg above 289 °C and 5% weight loss temperature (483–511 °C), and low CTE (11–68 ppm/°C). The effect of the substituent on molecular packing and properties, including optical and thermomechanical properties for the resulting PEsIs were examined in detail. The temperature-dependent CTE of the PEsIs was determined using molecular dynamics (MD) simulation. The molecular orbital (MO) calculation models support the discussions on the electronic substituent effect of the PEsI main chains. Our molecular architecture and systematic property studies with MD and MO promote a better understanding of the polyimides.

A facile one-step method for synthesis of a porous monolithic polyimide aerogel was successfully developed. The specific thermal curing, slow desiccating process and swelling method were used in synthesizing monolithic polyimide aerogel without any additional chemical reaction to create a connected structure among the polyimide-based spherical aerogel microparticles. Using this method, the monolithic polyimide aerogel can be easily fabricated whilst using no additional chemicals for crosslinking. This type of polyimide aerogel was produced homogeneously by the polyimidization of pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA). The synthesized porous monolithic polyimide aerogel has many good properties which could be used in various industries, as it maintained a high thermal decomposition temperature (10% weight decomposition temperature: T d10% ) of approximately 577 °C and a glass transition temperature (T g ) of 432 °C, with bulk density of 490.7 kg/m 3 , porosity of approximately 45% and average pore size of 4 nm (by nitrogen adsorption test) of polymer and 157 nm (by mercury intrusion method) of space observed in FE-SEM image. Also, the monolithic polyimide aerogel had an excellent oil-adsorbing capacity of 150%, and the adsorbed oil could be separated easily using a simple drying process. The dried monolithic polyimide aerogel showed significant recoverability and reusability of adsorbed oil. In addition, the monolithic polyimide aerogel exhibited high mechanical resistance such that the structure can withstand a high pressure greater than 122.3 kPa, under which the monolithic polyimide aerogel (MPA) was compressed but did not break. This type of MPA shows excellent thermal, mechanical properties and great processability, and could be the new candidate for high performance materials in various industries, especially catalyst field.

In development of modern electric fields, the growth of kinds of electronic devices has made the supply and research on heat dissipating films become important. To synthesize heat dissipation films with high thermal resistance for possible use in electronics applications, carbon black is doped into polyimide to increase the dissipating rate of films, at loadings of 50, 100, and 150 wt%. The resulting films display excellent thermal properties; the thermal conductivity of the film with 150 wt% carbon black is 5.59W∙m−1K−1, a value that is 35 times higher than that of pure polyimide (0.16W∙m−1K−1). To theoretically confirm the increased dissipating ability of composite films, the Nielsen equation is used for verification. The experimental results show an excellent fit with the theoretical values calculated by the Nielsen equation. The great thermal stability of polyimide composite film with carbon black is verified by using TGA and DSC, the temperature for 1% thermal decomposition of the 150wt% film is 541°C, and the glass transition temperature is 315 °C. The heat conduction results also show high heat dissipation data, which make the carbon black composite polyimide films an excellent candidate for use in electric devices to deplete the heat generated.

We report an efficient route for ferroelectric polar β phase generation in poly(vinylidene fluoride) (PVDF) through incorporation of amine functionalized, porous silica (MCM-41 and fumed silica) based nanofillers. These porous highly functionalized surfaces exhibit the efficient secondary interaction with polymer chain via hydrogen bonding. Structural analysis through FTIR, XRD, and TEM confirm high degree of ferroelectric polar β phase generation of PVDF through incorporation of amino modified porous silica nanofillers. Optimized loading (5 wt %) of amine functionalized, porous silica in PVDF matrix enhances relative intensity of β phase up to 75%. Disappearance of spherulite structure of PVDF with amino modified porous silica nanofillers, as confirmed through POM, TEM, SEM and AFM studies also supports the above conclusion. The P-E hysteresis loop at sweep voltage of ±50 V of a thin PVDF-amino modified porous nanofiller film shows excellent ferroelectric property with nearly saturated high remnant polarization 2.8 µC.cm−2 owing to its large proportion of β PVDF, whereas, a nonpolar pure PVDF thin film shows unsaturated hysteresis loop with 0.6 µC.cm−2 remnant polarization. PVDF films with the nanofillers exhibit strong adhesive strength over different metallic substrates making them have edge over PVDF in various thin film applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2401–2411

Supercritical methanol is a popular fluid as a supercritical medium for decrosslinking reaction of crosslinked polyethylene. However, due to its toxicity, a safe alternative medium is much to be desired. In this work, various sub- and supercritical fluids with different polarity characters were investigated to find a safe alternative medium for continuous decrosslinking of silane-crosslinked polyethylene (S-XLPE). Like methanol, all examined fluids, including ethanol, propanol, and water, exhibited first-order reaction kinetics regarding the gel content in the continuous decrosslinking process. The reaction rate constant values were observed as 2.806, 2.569, 2.383, and 2.130 min −1 in supercritical methanol, supercritical ethanol, supercritical 2-propanol, and subcritical water at 380 °C, respectively. As a non-toxic fluid with reaction kinetics very comparable to that of methanol, ethanol was found to be the best alternative medium for the continuous decrosslinking reaction of S-XLPE.

For the first time, a kinetic study on the supercritical decrosslinking reaction of silane-crosslinked polyethylene (S-XLPE) in a continuous process was conducted. The decrosslinking reaction in a continuous process was corresponding to the first-order reaction model in which the reaction rate was linearly proportional to the gel content. The residual gel content exponentially decreased with reaction time. Reaction constant was observed exponentially related to the reaction temperature. The continuous decrosslinking reaction revealed kinetic constants of 1.355 ± 0.103, 2.715 ± 0.177, and 4.348 ± 0.218 min −1 at 360, 380 and 390 °C, respectively and activation energy of 132.36 kJ mol −1 .

A polyimide aerogel (PIA) was used to synthesize low-dielectric-constant polyimide composite films. Unlike silica aerogel (SIA) composites, the PIA films were synthesized using polyimide. The resulting films maintained the original thermal and chemical properties of polyimide, which contribute to their homogeneity. The dielectric constant of the aerogel composite film was decreased to ~2.4, a value similar to that of a SIA composite film. The increase in dielectric constant as a result of water adsorption exhibited by SIA films was counteracted by the hydrophobicity of the polyimide in the PIA film. The PIA composite film exhibited a 3% water uptake, compared with a 29% water uptake in the SIA film, indicating that the polyimide film is the preferred choice in wet conditions. The presence of a uniformly dispersed aerogel, a 1% thermal decomposition temperature of 589 °C and a glass transition temperature of 298 °C for the PIA composite film were confirmed by field emission scanning electron microscopy, thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC) analysis, respectively. The TGA and DSC results demonstrated that the excellent thermal properties of polyimide were maintained in the PIA composite film. Polyimide aerogel (PIA) was used to synthesize low-dielectric-constant polyimide composite films. Unlike silica aerogel composites, the polyimide aerogel composite films were synthesized solely based on polyimide. The films maintained the original thermal and chemical properties of polyimide contributing to their homogeneity. The presence of uniformly dispersed aerogel, the high-thermal decomposition and glass transition temperature of the PI–PIA sample films were confirmed by field emission scanning electron microscope, TGA and DSC analysis. The FE-SEM image of the PI–PIA film samples indicates that the PIA particles were well-dispersed in the film and retained their spherical shape.

The changes to Ubiquitous Network Environment leads existing learning environment to Smart Learning Environment. Expecially, Smart Learning Environment is in changing paradigm existing teacher centered environment and learner centered environment, recently the demand of Smart Learning Environment for learners are growing up. This study analyzed Learning Environments for Smart Learning Environment focused on the learners through analyzing Ubiquitous Network Environment that is concentrated on the physical aspects and the non-physical aspects. Also, we suggested learning several ways that can be effectively applied based on the environmental characteristics of Smart Learning.

In this study, poly(amide-imide)s are synthesized for electronic materials by adding amide groups into polyimide. As it is expected, poly(amide-imide) shows an amorphous structure with a lower glass transition temperature and residual stress than the neat polyimide due to the high steric hindrance of the amide group. Also, the modification to the polyimide structure leads to higher transmittance and enhances colorless properties. Consequently, successful synthesis of poly(amide-imide)s is demonstrated which has wide applicability in the electronic industries due to their low glass transition temperature. It is expected that semiconductor and integrated circuit products can be manufactured utilizing poly(amide-imide)s with high reliability and a low chance of cracking due to their lower residual stress. Furthermore, it envisioned that the improved optical properties of poly(amide-imide) materials will allow for their applications in transparent displays and coating products.

Graphene nanoparticles coated with tannic acid were synthesized as non-halogen flame retardants; further, these nanoparticles were electrospun with polyurethane to produce multifunctional composite nanofibers. The composite nanofibers showed improved flame retardant, antimicrobial, and mechanical properties with increasing amounts of bio-based, non-halogen flame retardant. For instance, at 5 wt% of flame retardant, the peak heat release rate was reduced from 340.75 to 235.23 W/g along with 500% and 135% improvement in the antimicrobial activity and Young's modulus, respectively, compared to neat polyurethane fibers. These multifunctional composite nanofibers have potential applications in various fields, such as automobile, construction, and biomedical device.

Simple self-healing behavior of polymers that respond to multiple physicochemical stimuli are highly desirable for industrial applications. In this study, under various external environmental stimulating factors, we focus on the self-healing kinetics of polymer bilayer films (PBFs) comprising a colorless polyimide (CPI) bottom-substrate layer and linseed oil loaded microcapsule (LOMC)-embedded polydimethylsiloxane (PDMS) upper-healing layer. The experimental results showed clear correlation between stimulating factors and the healing time. Although the crack-healing behavior of PBF with 5 wt% microcapsule under air atmosphere is fairly slow, it has an improved healing effect at the artificial crack interface heating to 70 °C; moreover, gradual healing is observed by moisture absorption in environments with relative humidity of 70%. Remarkably, we found that ultraviolet (UV)-light irradiation through the 5 wt% LOMC-filled PDMS layer triggers a noticeable kinematic advantage for the drying reaction that initiates interfacial self-healing. Short-time (20 min) UV-irradiated PBF 5 wt% exhibits a low water vapor permeability of 35.4 g m−2 day−1 and excellent healability with ~91% recovery by single capsule-type photochemical-induced self-healing. The proposed approach advances the extrinsic healing of colorless polymers in a kinetically effective way without compromising their chemical composition.

Molten carbonate fuel cell (MCFC) is a high-temperature fuel cell for power plants. Since MCFC is operated at approximately 650 °C, the lifetime of the MCFC is limited by the thermal degradation of MCFC components. To reduce thermal degradation, the lower temperature for long-term operation is suggested. However, the electrochemical reaction on the cathode becomes slower at the lower operational temperature. To improve the performance for the long-term operation of MCFC, a ZrO2 coated cathode was fabricated by atomic layer deposition. The cell using the ZrO2 coated cathode showed a high voltage of 0.867 V at a temperature of 600 °C and a current density of 150 mA/cm2. The charge transfer resistance is also reduced dramatically at that same time. It can be confirmed that the high cell performance is presented when the electron-rich environment of NiO by ZrO2 coating improved the performance of the cell. Also, the cell using the ZrO2 coated cathode kept a stable performance over 2,000 h due to the prevention of NiO sintering by the uniform ZrO2 coating layer.

To cope with the demand for cleaner alternative energy, polymer electrolyte membrane fuel cells (PEMFCs) have received significant research attention owing to their high-power density, high fuel efficiency, and low polluting by-product. However, the water requirement of these cells has necessitated research on systems that do not require water and/or use other mediums with higher boiling points. In this work, a highly porous meta-polybenzimidazole (m-PBI) membrane was fabricated through the non-solvent induced phase inversion technique and thermal cross-linking for high-temperature PEMFC (HT-PEMFC) applications. Standard non-thermally treated porous membranes are susceptible to phosphoric acid (PA) even at low concentrations and are unsuitable as polymer electrolyte membranes (PEMs). With the porous structure of m-PBI membranes, higher PA uptake and minimal swelling, which is controlled via cross-linking, was achieved. In addition, the membranes exhibited partial asymmetrical morphology and are directly applicable to fuel cell systems without any further modifications. Membranes with insufficient cross-linking resulted in an unstable performance in HT-PEMFC environments. By optimizing thermal treatment, a high-performance membrane with limited swelling and improved proton conductivity was achieved. Finally, the m-PBI membrane exhibited enhanced acid retention, proton conductivity, and fuel cell performance.

In recent times, with increase of requirements in function and appearance, it is important to improve the function of package components which are implemented in various electronic devices by developing reliable packaging technology such as wafer level chip scale packaging (WLCSP). For the package, insulation techniques are essential to reduce noise caused by high electrical current and overcome coefficient of thermal expansion (CTE) mismatch between interfaces of multi-layers. In this study, in order to investigate properties of polyimide based materials for WLCSP as dielectrics, a series of copolyimide/silica nanocomposite (CPS) films were prepared from sol-gel method and their residual stress behavior on Si wafer was evaluated in situ during thermal cure and cooling steps. This work provides a possible candidate for application in WLCSP industries by controlling desirable properties.