• Journal of Sensor Science and Technology
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• v.32 no.3
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• pp.169-173
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• 2023

With the increasing concern of global warming caused by greenhouse gases owing to the recent industrial development, there is a growing need for advanced technology to control these emissions. Among the various greenhouse gases, nitrogen dioxide (NO₂) is a major contributor to global warming and is mainly released from sources, such as automobile exhaust and factories. Although semiconductor-type NO₂ gas sensors, such as SnO₂, have been extensively studied, they often require high operating temperatures and complicated manufacturing processes, while lacking selectivity, resulting in inaccurate measurements of NO₂ gas levels. To address these limitations, a novel sensor using PbS quantum dots (QDs) was developed, which operates at low temperatures and exhibits high selectivity toward NO₂ gas owing to its strong oxidation reaction. Furthermore, the use of P3HT conductive polymer improved the thin film quality, reactivity, and reaction rate of the sensor. The sensor demonstrated the ability to accurately measure NO₂ gas concentrations ranging from 500 to 100 ppm, with a 5.1 times higher sensitivity, 1.5 times higher response rate, and 1.15 times higher recovery rate compared with sensors without P3HT.

• Applied Chemistry for Engineering
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• v.5 no.5
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• pp.764-771
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• 1994

Electrochemical synthesis of conductive polypyrrole films was carried out in nucleophilic solvent containing p-toluenesulfonic acid or bezensulfonic acid as supporting electrolyte and dopant. Also characteristics of degradation and improvement of mechanical properties were studied. The conductivity, tensile strength and elongation of the films obtained in dimethyformamide/p-toluenesulfonic acid had the highest value of 10-40S/cm, $25N/mm^2$ and 10%, respectively. The optimum condition of electrochemical synthesis was $2mA/cm^2$ for constant current method and 0.9V for constant potential method containing 0.5M pyrrole and 0.5M p-TSA. The obtained films showed good stability in air and electrode characteristics of secondary battery by reversibility in doping and undoping. The degradation process was 1st order reaction at various temeprature. The activation energy and rate constant of degradation reaction were $1.01JK^{-1}mol^{-1}$ and $3.1{\times}10^{-7}min^{-1}$ respectively at $25^{\circ}C$. For the improvement of mechanical properties, composition of polypyrrole films with various host polymer were investigated and increase of tensile strength and elongation was confirmed.

• Journal of Korean Society of Steel Construction
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• v.16 no.5 s.72
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• pp.609-619
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• 2004

An investigation was conducted on the activities around Europe in order to solve the problem of the thermal bridging of steel studs, which had caused a significant disadvantage. This study included the following: diminishing the contact area between the studs and the sheathing, lengthening the heat transfer route, replacing the steel web with a less conductive material, and placing foam insulation in locations where the thermal shorts are most critical. Although energy efficiency is usually the focus of such foreign cases because their stud application is mostly limited to low-rise residential buildings, both structural and thermal performance are taken into consideration in this study because these target middle-story buildings. A hybrid stud composed of steel and polymer was also developed. This hybrid stud, which is 150 SL in size, is made of a galvanized steel sheet (SGC58) and a glass fiber reinforced polymer (GFRP) withepoxy bonding. A total of 32 specimens were manufactured. Its parameters comprise two types of connection detail,s: the thickness of steel (1.0mm and 1.2mm) and of the GFRP (4mm-4ply and 6mm-6ply), and the ratio of the length to the depth (L/D = 3, 6, 9, 12). Steel stud specimens with the same conditions were compared to the hybrid stud. The test revealed that in the case of the steel specimen with a thickness of 1.0mm, the maximum load of hybrid studs increased an average of 1.62 times comparedto that of the steel stud. In the case of the steel specimen with a thickness of 1.2mm, on the other hand, the average increase was 1.46times. All specimens showed full composite action until the collapse.

• Polymer(Korea)
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• v.35 no.5
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• pp.472-477
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• 2011

To study the effects of the acid group of functionalized MWNT (multiwalled carbon nanotube) on the thermal and mechanical properties of polyacrylonitrile(PAN) nanofibers, acid ($H_2SO_4/HNO_3$) treated MWNT (O-MWNT) were further functionalized by diazonium salt reaction with 5-aminoisophthalic acid (IPA). Compared to O-MWNT, IPA-MWNT with isophthalic acid group showed a better dispersion stability in polar solvents and IPA-MWNT/PAN composite film displayed lower heat of reaction (${\Delta}H$) than that of homo PAN when stabilized under air atmosphere. The continuous electrospun fibers were prepared using a conductive water bath. PAN fibers containing 1 wt% of IPA-MWNT showed an increase of tensile strength by 100% and tensile modulus by 240% compared to the PAN fibers without IPA-MWNT.

• Journal of Adhesion and Interface
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• v.9 no.3
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• pp.7-13
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• 2008

The particulate type silicon carbide (SiC) and fiber type carbon fiber (CF) filler, of similar thermal conductivities, were mixed with polyetheretherketone (PEEK) to investigate the filler effects on the thermal diffusivity. The SiC and CF fillers had a good and uniform dispersion in PEEK matrix. Thermal diffusivities of PEEK composites were measured from ambient temperature up to $200^{\circ}C$ by laser flash method. The diffusivities were decreased as increasing temperature due to the phonon scattering between PEEK-filler and filler-filler interfaces. Thermal diffusivity of PEEK composites was increased with increasing filler content and the thermal conductivities of two-phase system were compared to the experimental results and it gave ideas on the filler dispersion, orientation, aspect ratio, and filler-filler interactions. Nielson equation gave a good prediction to the experimental results of PEEK/SiC. The easy network formation by CF was found to be substantially more effective than SiC and it gave a higher thermal diffusivities of PEEK/CF than PEEK/SiC.

• Membrane Journal
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• v.32 no.6
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• pp.411-426
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• 2022

Energy plays a significant role in modern lifestyle because of our extensive reliance over energy-operating devices. Therefore, there is a need for alternative and green energy resources that can fulfill the energy demand. For this, fuel cell (FCs) especially anion exchange membrane fuel cells (AEMFCs) have gained tremendous attention over the other (FCs) due to their fast reaction kinetics without using noble catalyst and allow to use of cheaper polymers with high performance. But lack of highly conductive, chemically, and mechanically stable anion exchange membrane (AEM) still main obstacle to the development of high performance AEMFCs. Therefore, graphene-based polymer composite membranes came into the existence as AEMs for the FCs. The exceptional properties of the graphene help to improve the performance of AEMs. Still, there are lot of challenges in the graphene derivatives based AEMs because of their high tendency of agglomeration in polymer matrix which reduced their potential. To overcome this issue surface modification of graphene derivatives is necessary to restrict their agglomeration and conserved their potential features that can help to improve the performance of AEM. Therefore, this review focus on the surface modification of graphene derivatives and their role in the fabrication of AEMs for the FCs.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.100-101
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• 2012

The plasma damage free and room temperature processedthin film deposition technology is essential for realization of various next generation organic microelectronic devices such as flexible AMOLED display, flexible OLED lighting, and organic photovoltaic cells because characteristics of fragile organic materials in the plasma process and low glass transition temperatures (Tg) of polymer substrate. In case of directly deposition of metal oxide thin films (including transparent conductive oxide (TCO) and amorphous oxide semiconductor (AOS)) on the organic layers, plasma damages against to the organic materials is fatal. This damage is believed to be originated mainly from high energy energetic particles during the sputtering process such as negative oxygen ions, reflected neutrals by reflection of plasma background gas at the target surface, sputtered atoms, bulk plasma ions, and secondary electrons. To solve this problem, we developed the NBAS (Neutral Beam Assisted Sputtering) process as a plasma damage free and room temperature processed sputtering technology. As a result, electro-optical properties of NBAS processed ITO thin film showed resistivity of $4.0{\times}10^{-4}{\Omega}{\cdot}m$ and high transmittance (>90% at 550 nm) with nano- crystalline structure at room temperature process. Furthermore, in the experiment result of directly deposition of TCO top anode on the inverted structure OLED cell, it is verified that NBAS TCO deposition process does not damages to the underlying organic layers. In case of deposition of transparent conductive oxide (TCO) thin film on the plastic polymer substrate, the room temperature processed sputtering coating of high quality TCO thin film is required. During the sputtering process with higher density plasma, the energetic particles contribute self supplying of activation & crystallization energy without any additional heating and post-annealing and forminga high quality TCO thin film. However, negative oxygen ions which generated from sputteringtarget surface by electron attachment are accelerated to high energy by induced cathode self-bias. Thus the high energy negative oxygen ions can lead to critical physical bombardment damages to forming oxide thin film and this effect does not recover in room temperature process without post thermal annealing. To salve the inherent limitation of plasma sputtering, we have been developed the Magnetic Field Shielded Sputtering (MFSS) process as the high quality oxide thin film deposition process at room temperature. The MFSS process is effectively eliminate or suppress the negative oxygen ions bombardment damage by the plasma limiter which composed permanent magnet array. As a result, electro-optical properties of MFSS processed ITO thin film (resistivity $3.9{\times}10^{-4}{\Omega}{\cdot}cm$, transmittance 95% at 550 nm) have approachedthose of a high temperature DC magnetron sputtering (DMS) ITO thin film were. Also, AOS (a-IGZO) TFTs fabricated by MFSS process without higher temperature post annealing showed very comparable electrical performance with those by DMS process with $400^{\circ}C$ post annealing. They are important to note that the bombardment of a negative oxygen ion which is accelerated by dc self-bias during rf sputtering could degrade the electrical performance of ITO electrodes and a-IGZO TFTs. Finally, we found that reduction of damage from the high energy negative oxygen ions bombardment drives improvement of crystalline structure in the ITO thin film and suppression of the sub-gab states in a-IGZO semiconductor thin film. For realization of organic flexible electronic devices based on plastic substrates, gas barrier coatings are required to prevent the permeation of water and oxygen because organic materials are highly susceptible to water and oxygen. In particular, high efficiency flexible AMOLEDs needs an extremely low water vapor transition rate (WVTR) of $1{\times}10^{-6}gm^{-2}day^{-1}$. The key factor in high quality inorganic gas barrier formation for achieving the very low WVTR required (under ${\sim}10^{-6}gm^{-2}day^{-1}$) is the suppression of nano-sized defect sites and gas diffusion pathways among the grain boundaries. For formation of high quality single inorganic gas barrier layer, we developed high density nano-structured Al2O3 single gas barrier layer usinga NBAS process. The NBAS process can continuously change crystalline structures from an amorphous phase to a nano- crystalline phase with various grain sizes in a single inorganic thin film. As a result, the water vapor transmission rates (WVTR) of the NBAS processed $Al_2O_3$ gas barrier film have improved order of magnitude compared with that of conventional $Al_2O_3$ layers made by the RF magnetron sputteringprocess under the same sputtering conditions; the WVTR of the NBAS processed $Al_2O_3$ gas barrier film was about $5{\times}10^{-6}g/m^2/day$ by just single layer.

• Composites Research
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• v.30 no.2
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• pp.138-144
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• 2017

Damage sensing of polymer composite films consisting of poly(dicyclopentadiene) p-DCPD and carbon nanotube (CNT) was studied experimentally. Only up to 1st ring-opening polymerization occurred with the addition of CNT, which made the modified film electrically conductive, while interfering with polymerization. The interfacial adhesion of composite films with varying CNT concentration was evaluated by measuring the wettability using the static contact angle method. 0.5 wt% CNT/p-DCPD was determined to be the optimal condition via electrical dispersion method and tensile test. Dynamic fatigue test was conducted to evaluate the durability of the films by measuring the change in electrical resistance. For the initial three cycles, the change in electrical resistance pattern was similar to the tensile stress-strain curve. The CNT/p-DCPD film was attached to an epoxy matrix to demonstrate its utilization as a sensor for fracture behavior. At the onset of epoxy fracture, electrical resistance showed a drastic increase, which indicated adhesive fracture between sensor and matrix. It leads to prediction of crack and fracture of matrix.

• Applied Chemistry for Engineering
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• v.7 no.5
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• pp.954-962
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• 1996

Four kind of polysilanes which had side chains of methyl, phenyl, and mixed structures, were synthesized and modified by doping with iodine. The structural, thermal, and electric characteristics of obtained polymers were systematically observed with iodine, The structural, thermal, and electric characteristics of obtained polymers were systematically observed with FT-IR, UV/VIS, TGA/DTG, DSC, and measurement of electric conductivity. From FT-IR spectra, it was confirmed that the synthesized polysilanes had side chains of methyl, phenyl, and mixed structures. The thermal stabilities of the polymers were found to increase with phenyl substituents. The polysilanes with phenyl side groups showed ${\sigma}-{\sigma}*$ transition absorption at wavelengths longer than 350 nm. The bathochromic shift of polysilanes with phenyl substituents relates probably to the narrowed band gap caused by delocalization of ${\pi}$-electron. The polymers doped with iodine showed multi-step pyrolysis behavior and higher residue compared with that of the undoped polymers. The electric conductivities of the undoped and doped polysilanes were $10^{-5}S/cm$ and $10^{-4}S/cm$, respectively.

• Journal of Energy Engineering
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• v.20 no.3
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• pp.171-177
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• 2011

PVA/GLA/$Al_2O_3{\cdot}3SiO_2$ composite membranes were prepared through the reaction polyvinyl alcohol (PVA) with glutaraldehyde (GLA) as a cross-linking agent and subsequently adding aluminum silicate ($Al_2O_3{\cdot}3SiO_2$) as an inorganic material. The water uptake decreased as the GDL contents increased due to cross-linking process of PVA with GDL, and the ion conductivity increased as the $Al_2O_3{\cdot}3SiO_2$ contents increased in PVA/GLA/$Al_2O_3{\cdot}3SiO_2$ composite membranes. The cross-linking structure of the polymers was confirmed using IR and the tendency of water uptake. The thermal analysis of the copolymers was carried out by TGA. TGA results showed that PVA/GLA composite membrane were more heat-resistant than PVA due to the cross-linking of PVA, and the heat stability of the composite membranes improved much more as the concentration of $Al_2O_3{\cdot}3SiO_2$ increased. Membranes prepared in this study seem to be have thermal stability and increase a tendency of the cation conductivity up to $60^{\circ}C$, but to be exhibit lower performance tendency at over $90^{\circ}C$. Therefore, it is necessary to do more aggressive effort to explore the possibility of application as an ion-conductive composite electrolyte.