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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 ...

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.

It is developing an engine for an unmanned aerial vehicle that performs missions without a person in the turboshaft method. This engine is equipped with a recuperator to drive the engine with higher efficiency, which can extend the distance for performing a given aircraft’s mission. This study evaluates the various performances (heat exchange efficiency and pressure loss) of a recuperator developed for the purpose of installing it on the 100-horsepower engine and conducts the tests in various engine driving environments. These results can more accurately predict the performance of the engine to be developed and can serve as an opportunity to further increase engine efficiency.

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

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.

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.

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°.

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.

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.

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.

We herein report an effective way to fabricate high-performance polybenzimidazole (PBI) nanocomposite membranes using sulfophenylated titanium oxide (s-TiO2) nanoparticles for application in high temperature polymer electrolyte membrane fuel cell (HT-PEMFC). The s-TiO2, multifunctional inorganic proton conductors that can improve proton conductivity and cell performance of PBI, was obtained through the surface modification. The PBI nanocomposite membranes were doped with phosphoric acid (PA) for performance evaluation. Properties such as PA doping level, proton conductivity, PA retention and cell performance were evaluated and compared to neat PBI. PA doped PBI-sTP2 (2 wt% TiO2) showed the highest doping of 12.1 and proton conductivity of 0.096 S/cm at 150 °C. In the cell test, peak power density of 621 mW/cm2 was obtained, roughly 30% better performance compared to neat PBI (471 mW/cm2).

In this study, the swelling method for controlling the pore size of the polyimide aerogel is demonstrated. The swelling method allows the pore size to be increased by changing the spherulitic formation. This newly developed method is simple and hardly affects original polymer chain and thus can be applied to a variety of precursor polymers without hindering the synthesis process. Unlike other methods, no foreign additives such as additional chemicals or crosslinkers are required to enlarge the pores of the aerogel, which contributes to higher homogeneity of the material. In order to test its effectiveness in pore size control and observe its behavior with different polyimides, various monomers—pyromellitic dianhydride, 3,3′,4,4′-benzophenonete-trac-arboxylic dianhydride, and 4,4′-oxydiphthalic anhydride—were tested to verify the potential of the proposed method. Depending on different polymer backbone, each aerogel showed a similar slope but different increase rate of the pore size. The retained thermal and structural properties of the synthesized aerogels were confirmed by thermogravimetric analysis, differential scanning calorimetry, and Fourier-transform infrared spectroscopy. This newly proposed simple method showed its effectiveness in increasing the pore sizes, enlarging the mesopore size from 4 nm to 20 nm and total pore volume from 1.29 cm 3 / g to 2.06 cm 3 / g for swollen aerogel when pyromellitic dianhydride was used. Also, the surface area increased from 54 m 2 / g to 88 m 2 / g , and the porosity increased from 58% to 73%.

The current paper describes enhanced electrochemical capacitive performance of chemically grown Cobalt hydroxide (Co(OH)2) nanorods (NRs) decorated porous three dimensional graphitic carbon foam (Co(OH)2/3D GCF) as a supercapacitor electrode. Freestanding 3D porous GCF is prepared by carbonizing, high internal phase emulsion (HIPE) polymerized styrene and divinylbenzene. The PolyHIPE was sulfonated and carbonized at temperature up to 850 °C to obtain graphitic 3D carbon foam with high surface area (389 m2 g−1) having open voids (14 μm) interconnected by windows (4 μm) in monolithic form. Moreover, entangled Co(OH)2 NRs are anchored on 3D GCF electrodes by using a facile chemical bath deposition (CBD) method. The wide porous structure with high specific surface area (520 m2 g−1) access offered by the interconnected 3D GCF along with Co(OH)2 NRs morphology, displays ultrahigh specific capacitance, specific energy and power. The Co(OH)2/3D GCF electrode exhibits maximum specific capacitance about ~1235 F g−1 at ~1 A g−1 charge-discharge current density, in 1 M aqueous KOH solution. These results endorse potential applicability of Co(OH)2/3D GCF electrode in supercapacitors and signifies that, the porous GCF is a proficient 3D freestanding framework for loading pseudocapacitive nanostructured materials.

Page 1115, the Acknowledgments should be corrected as follows: This work was supported by the KIST Institutional Program (Project No. 2E26600-16-041) and National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2017R1D1A1B03033332).

This paper presents the heat transfer and pressure drop characteristics of a primary surface heat exchanger (PSHE) with corrugated surfaces. The PSHE was experimentally investigated for a Reynolds number range of 156–921 under various flow conditions on the hot and cold sides. The inlet temperature of the hot side was maintained at 40 °C, while that of the cold side was maintained at 20 °C. A counterflow was used as it has a higher temperature proximity in comparison with a parallel flow. The heat transfer rate and pressure drop were measured for various Reynolds numbers on both the hot and cold sides of the PSHE, with the heat transfer coefficients for both sides computed using a modified Wilson plot method. Based on the results of the experiment, both Nusselt number and friction factor correlations were suggested for a PSHE with corrugated surfaces.