• Membrane Journal
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• v.25 no.3
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• pp.287-294
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• 2015

Photovoltaic (PV) modules are environmentally friendly energy-conversion devices to generate electricity via the photovoltaic effect of semiconductors on solar energy. One of key elements in PV modules is "Backsheet," a multi-layered film to protect the devices from a variety of chemicals including water vapor. A representative Backsheet is composed of polyvinyl fluoride (PVF) and poly(ethylene terephthalate) (PET). PVF is relatively expensive, while showing excellent resistance to chemical attacks. Thus, it is necessary to develop alternatives which can lower its high production cost and guarantee lifetime applicable to practical PV modules at the same time. In this study, PET films with certain levels of crystallinity were utilized instead of PVF. Since it is well known that PET is suffering from trans-esterification and hydrolysis under a wide pH range, it is needed to understand decomposition behavior of the PET films under PV operation conditions. To evaluate their chemical decomposition behavior within a short period of times, accelerated decomposition test protocol is developed. Moreover, electrochemical long-term performances of the PV module employing the PET-based Backsheet are investigated to prove the efficacy of the proposed concept.

• Composites Research
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• v.35 no.6
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• pp.394-401
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• 2022

Two polymer precursors, polyvinylidene chloride-resin (PVDC-resin) and polyvinylidene fluoride (PVDF), are assembled into the microporous carbon by pyrolysis. Microporous carbon is advantageous as an electrode for supercapacitors that store electric charges through ion adsorption/desorption. The pyrolysis also turns the various heteroatoms of two precursors into functional groups, contributing to the additional charge storage. The analysis of the porous structure and function group during carbonization are important to develop the carbon for energy storage. Here, we analyzed the functional groups of two polymer-derived carbons through X-ray photoelectron spectroscopy. The electrochemical properties of the functional groups were explored in various pH electrolytes. The specific capacitance of two carbons in the acidic electrolyte (1 M H₂SO₄) was improved compared to that in the neutral electrolyte (0.5 M Na₂SO₄) due to the faradaic charge/discharge reaction of the quinone functional group. In particular, the carbon electrode derived from PVDC-resin exhibits a lower capacity than the carbon from PVDF due to the small micropores. In the alkaline electrolyte (6 M KOH), the highest specific capacitance and rate capability were obtained among the three electrolytes for both electrodes based on the facile adsorption of the constituent electrolyte ions (K⁺, OH^-).

• Fibers and Polymers
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• v.4 no.4
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• pp.188-194
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• 2003

Phase behavior and spinodal phase separation kinetics in binary blends of a random copolymer of vinylidene fluoride and trifluoroethylene (75/25) [P(VDF/TrFE)] and poly(l,4-butylene adipate) (PBA) have been investigated by means of optical microscopic observation and time-resolved light scattering. The blends exhibited a typical lower critical solution temperature (LCST)∼${34}^{\circ}C$ above the melting temperature of the P(VDF/TrFE) crystals over the entire blend composition range. P(VDF/TrFE) and PBA were totally miscible in the temperature gap between the melting point of P(VDF/TrFE) and the LCST. Temperature jump experiments of the 3/7 P(VDF/TrFE)/PBA blend were carried out on a light-scattering apparatus from a single-phase melt state (${180}^{\circ}C$) to a two-phase region (205∼${215}^{\circ}C$). Since the late stage of spinodal decomposition (SD) is prevalent in the 3/7 blend, SD was analyzed using a power law scheme. Self-similarity was preserved well in the late stage of SD in the 3/7 blend.

• Journal of Korean Dental Hygiene Science
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• v.3 no.2
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• pp.1-8
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• 2020

This study investigated the relationship between oral health knowledge, behavior and orthodontic satisfaction in orthodontic patients visiting dental hospitals and clinics and provided suggestions to improve orthodontic patients' satisfaction. This study anayzed structured self-administered questionnaires collected from 245 patients who visited 5 dental clinics in Gwangju Metropolitan City. Regarding oral health knowledge, the highest percentage of correct answers was for the item "Cavities heal themselves over time" (97.1%), and the lowest percentage of correct answers was for the item "Cavity bacteria move from tooth to tooth" (16.7%). Five fluoride items showed a lower percentage of correct answers than those for cavity and gingival diseases. Regarding the survey on oral health behavior, the highest score was found for the item "I brush my teeth with a certain method and order" (3.78 out of 5), and the lowest score was found for the item "I use an electric toothbrush" (1.34 out of 5). Regarding the survey on orthodontic satisfaction, the highest score was found for the item "I would recommend receiving medical treatment at the department of orthodontics" (4.23), and the lowest score was found for the item "Orthodontic cost is reasonable" (3.46). While oral health behavior had on orthodontic satisfaction, oral health knowledge had no effect on it. Oral health behaviors should be improved to enhance orthodontic satisfaction. To improve oral health behavior, it is necessary to develop and activate education programs for tooth brushing and oral care for orthodontic patients.

• The Korean Journal of Health Service Management
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• v.8 no.4
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• pp.141-147
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• 2014

Dental clinic programs for elementary school children to live healthy life by promote healthy lives by oral health self-management skills. This study on schools with and without dental clinics compared and analyze teacher's knowledge of and attitudes toward oral care and determines whether or not to recommend the school dental clinic program. The subjects of the study were 239 teachers in schools with dental clinics and 201 teachers in schools without dental clinics. In total, the study included 20 schools and 440 teachers. Teachers from schools with dental clinics had a higher recognition rate of the purpose of tooth brushing and the fluoride caries preventive effect than teachers from schools without dental clinics. However, there was no significant difference between schools with and without dental clinics when we compared the daily tooth brushing frequency and oral health attitude. There is also need of a school dental clinic program for teachers because if teachers lack knowledge and professionalism of oral health it will affect the student's oral health attitudes.

• Journal of Korean society of Dental Hygiene
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• v.14 no.2
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• pp.173-179
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• 2014

Objectives : The purpose of this study is to provide the basic data for the development of oral health education program and to make schoolchildren practice the right oral health care behaviors. Methods : Data were collected from 259 elementary school students including 134 boys and 125 girls in Busan from November 26 to December 20, 2012. The groups were tooth brushing group and dental clinic group. All statistical analyses were analyzed by frequency analysis and chi-square test using SPSS 18.0 program. Results : School dental clinic group showed higher awareness level of fluoride and sealant effect of prevention(p=0.000). Toothbrushing facility group showed higher awareness level of brushing tooth(p=0.011). School dental clinic group showed higher awareness level of fluoride toothpaste(p=0.000). Both school dental clinic group and toothbrushing facility group showed higher awareness level of oral health education(p=0.001). School dental clinic group showed higher awareness level for tooth brushing method after education(p=0.000). Both school dental clinic group and toothbrushing facility group showed higher level of education. Conclusions : School dental clinic group showed higher level for oral health knowledge and toothbushing facility group showed high level for oral health behavior. Both School dental clinic group and toothbrushing facility group showed higher level of oral health education and tooth brushing method after education. Both school dental clinic group and toothbrushing facility group proved to promote oral health. Activation of school toothbrushing facility is very important to change the oral health workforce.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.169-170
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• 2006

In this study, ultra thin films of ferroelectric vinylidene fluoride-trifluoroethylene (VF2-TrFE) copolymer were fabricated on degenerated Si (n+, $0.002\;{\Omega}{\cdot}cm$) using by spin coating method. A 1~5 wt% diluted solution of purified vinylidene fluoride-trifluoroethylene (VF2:TrFE=70:30) in a dimethylformamide (DMF) solvent were prepared and deposited on silicon wafers at a spin rate of 2000~5000rpm for 30 seconds. After annealing in a vacuum ambient at $200^{\circ}C$ for 60 min, upper gold electrodes were deposited by vacuum evaporation for electrical measurement. X-ray diffraction results showed that the VF2-TrFE films on Si substrates had $\beta$-phase of copolymer structures. The capacitance on $n^+$-Si(100) wafer showed hysteresis behavior like a butterfly shape and this result indicates clearly that the dielectric films have ferroelectric properties. The typical measured remnant polarization (2Pr) and coercive filed (EC) values measured using a computer controlled a RT-66A standardized ferroelectric test system (Radiant Technologies) were about $0.54\;C/cm^2$ and 172 kV/cm, respectively, in an applied electric field of ${\pm}0.75\;MV/cm$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.388-388
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• 2010

In this study, Ferroelectric vinylidene fluoride-trifluoroethylene (VF2-TrFE) copolymer films were directly deposited on degenerated Si (n+, $0.002\;{\Omega}{\cdot}cm$) using by spin coating method. A 1~5 wt% diluted solution of purified vinylidene fluoride-trifluoroethylene (VF2:TrFE = 70:30) in a dimethylformamide (DMF) solvent were prepared and deposited on silicon wafers at a spin rate of 2000 ~ 4000 rpm for 2 ~ 30 seconds. After annealing in a vacuum ambient at 100 ~ $200^{\circ}C$ for 60 min, upper aluminum electrodes were deposited by vacuum evaporation for electrical measurement. X-ray diffraction results showed that the VF2-TrFE films on Si substrates had $\beta$-phase of copolymer structures. The capacitance on highly doped Si wafer showed hysteresis behavior like a butterfly shape and this result indicates clearly that the copolymer films have ferroelectric properties. The typical measured remnant polarization ($P_r$) and coercive filed ($E_c$) values were about $5.7\;{\mu}C/cm^2$ and 710 kV/em, respectively, in an applied electric field of ${\pm}$ 1.5 MV/em. The gate leakage current densities measured at room temperature was less than $7{\times}10^{-7}\; A/cm^2$ under a field of 1 MV/cm.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.5
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• pp.522-528
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• 2011

Artificial basilar membranes made of PVDF(polyvinylidene fluoride) are manufactured using microfabrication processes. The mechanical behavior of PVDF artificial basilar membrane was measured to evaluate its performance as a mechanical frequency analyzer using scanning LDV(laser Doppler vibrometer). The experimental setup consists of the microfabricated artificial basilar membrane, a loud speaker connected to an amplifier for generating acoustic pressure of specific spectral pattern, and a scanning LDV with controlling unit for measuring the displacement of the membrane on the incoming acoustic stimulation. The microfabricated artificial basilar membrane was attached tightly upon a package containing a chamber which can be filled with silicone oil before placed on the experimental setup stage. The experiment results showed that the microfabricated artificial basilar membrane has a property as a mechanical frequency analyzer.

• Journal of Adhesion and Interface
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• v.16 no.3
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• pp.116-121
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• 2015

In this study, octadecyltrichlorosilane (OTS) has been used to replace fluoro-silanes which are much more expensive than OTS. In order to improve the mechanical and adhesive properties of coating layers, inorganic binders were separately synthesized based on sol-gel reaction in acidic condition. Since the synthesized silica nanoparticles gave only nano-scaled roughness, superhydrophobicity is not well obtained. Here, we present a new simple approach by intentionally inducing particle aggregation in the solution which is controlled by adjusting solvent amount. With selecting suitable sizes of silica nanoparticles, superhydrophobic surfaces were obtained with increasing the amount of organic solvents after surface hydrophobization using OTS, and an extremely water-repellent behavior was observed with zero sliding angle. This superhydrophobicity was achived only for the dielectric constant lower than 25, regardless of the composition of solvent, meaning that the dielectric constant could be an excellent indicator for fabricating superhydrobic surfaces induced by particle aggregation in the solution.