• Journal of the Korean Ceramic Society
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• v.53 no.6
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• pp.700-706
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• 2016

Etch rate, surface roughness and microstructure as plasma resistance were evaluated for six kinds of oxide glass with different compositions. Borosilicate glass (BS) was found to be etched at the highest etch rate and zinc aluminum phosphate glass (ZAP) showed a relatively lower etch rate than borosilicate. On the other hand, the etching rate of calcium aluminosilicate glass (CAS) was measured to be similar to that of sintered alumina while yttrium aluminosilicate glass (YAS) showed the lowest etch rate. Such different etch rates by mixture plasma as a function of glass compositions was dependent on whether or not fluoride compounds were formed on glass and sublimated in high vacuum. Especially, in view that $CaF_2$ and $YF_3$ with high sublimation points were formed on the surface of CAS and YAS glasses, both CAS and YAS glasses were considered to be a good candidate for protective coating materials on the damaged polycrystalline ceramics parts in semi-conductor and display processes.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1190-1192
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• 1995

Poly(vinylidene fluoride)(PVDF) is one of the most studied polymers in the latest date. The interest in PVDF lies in its remarkable piezoelectric and pyroelectric properties. Also, PVDF has at least four known crystalline structures(; they are referred to as the ${\alpha},\;{\beta},\;{\gamma}\;and\;{\alpha}_p$ phase or forms II, I, III and $IV_p$). In this study, the manufactured PVDF thin film through vapor deposition method had form II(; the glass at $70^{\circ}C$). This thin film was investigated by x-ray diffraction(XRD), Fourier Transform Infrared(FT-IR) spectroscopy and Differential Thermal Analysis(DTA). XRD and FT-IR indicate crystallization forms from the glass at $70^{\circ}C$ into form II.

• Journal of dental hygiene science
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• v.19 no.4
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• pp.288-293
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• 2019

Background: Dental caries is one of several prevalent oral diseases caused by dental plaque biofilms. This study evaluated the anti-cariogenic effects of a bamboo salt (BS) and sodium fluoride (NaF) mixture on oral bacteria. Methods: The effects of several mixtures of NaF and BS on acid production, growth, and adhesion to glass beads of Streptococcus mutans, and their anti-cariogenic properties were investigated. The growth of S. mutans was measured according to optical density at 3, 6, 9, 12, 15, 18, and 24 hours after treatment using spectrophotometry at a wavelength of 600 nm, while pH was measured using a pH meter. Adhesion of S. mutans was measured according to the weight of glass beads from each group before and after incubation. Gene expression was measured using real-time polymerase chain reaction. Acid production and growth patterns of S. mutans were compared using repeated measures analysis of variance, followed by Scheffe's post-hoc test. The Kruskal-Wallis test was used to compare adhesion, followed by the Mann-Whitney test. Gene expression in the experimental and control samples was compared using the Student's t-test. Results: Growth, acid production, and adhesion of S. mutans were inhibited in all experimental groups. Expression of gft and fructosyltransferase in S. mutans was inhibited in all groups. A mixture of NaF and BS significantly reduced growth, acid production, adhesion, and gene expression of S. mutans compared with the other groups. Conclusion: Results of the present study demonstrated that a mixture of NaF and BS was useful as a mouth rinse in preventing dental caries.

• The korean journal of orthodontics
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• v.28 no.5 s.70
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• pp.689-698
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• 1998

The purpose of this study was to evaluate the shear bond strength of light cured glass ionomer cement to enamel surface which treated with $37\%$ phosphoric acid, $10\%$ polyacrylic acid, $1.23\%$ acidulated phosphate fluoride gel and no etching agent. To compare the shear bond strength of glass ionomer cement, light-cured composite resin and chemically-cured composite resin were empoloyed as controls. Eight experiments groups were composed. 10 specimens of each group were bonded by metal bracket by tested in universal testing machine for shear bond strength, in stereoscope for adhesive remnants index. The data were evaluated statistically by SPSS/PC+. The results were as follows. 1. Among the groups of $37\%$ phosphoric acid treated and dry and bonded with light cured glass ionomer, light cured composite resin, and chemically cured composite resin, the shear bond strength of glass ionomer group showed no significant difference to the others, but the shear bond strength of chemically cured resin showed statistically lower than that of light cured resin (p<0.05). 2. The shear bond strengths of glass ionomer cement to enamel treated group with $1.23\%$ acidulated phosphate fluoride gel and $10\%$ polyacrylic acid and $37\%$ phosphoric acid showed statistically higher than that of no etched enamel group(p<0.U). 3. In the groups of glass ionomer cement, the presence of moisture was not significantly effect to the shear bond strength (p<0.05). 4. After debonding, no etched enamel group showed less residual materials on the enamel surface than the group of enamel etched with $37\%$ Phosphoric acid.

• Journal of the korean academy of Pediatric Dentistry
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• v.37 no.4
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• pp.429-437
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• 2010

The aim of this study was to evaluate the fluoride release and microhardness of Beautifil II as giomer(Group I), F2000 Compomer as compomer(Group II), GC Fuji II LC Capsule as resin-modified glass ionomer(Group III) and $Filtek^{TM}$ Z350 as composite resin(Group IV) according to time. Forty discs(5 mm diameter and 2 mm height) were prepared for each material. Each disc was immersed in 3 ml of de-ionized water within polyethylene tube and stored at $37^{\circ}C$. Evaluations were performed by pH/ISE meter for analysis of fluoride release and hardness testing machine for analysis of microhardness over 31 days. The results can be summarized as follows : 1. For all groups except group IV, the greatest fluoride release was observed after the first day of the study period and then dramatically diminished over time. On the 7th day of the study period, fluoride release level was stabilized. 2. Group III showed the highest fluoride release among test groups and then group II, group I were followed. Significant difference in cumulative fluoride release over 31 days was found between each groups. Group IV showed no fluoride release during study period. 3. Group IV showed the highest microhardness among test groups and then group I, group II, group III were followed. Significant difference in microhardness was found between each group, except between group I and group II. 4. After 31 days, microhardness was slightly diminished in every group. However, no significant difference was found.

• Journal of Electrical Engineering and Technology
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• v.13 no.4
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• pp.1692-1696
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• 2018

Ferroelectric $BaTiO_3$/poly(vinylidene fluoride) (PVDF) nanocomposite films were successfully prepared by mixing $BaTiO_3$ nano-particles into PVDF solution dissolved in dimethylformamide under ultrasonification. The mixture was casted onto glass petri dish and then annealed at $100^{\circ}C$ for 12 h in vacuum dry oven. Crystal structure and surface morphology of the samples were analyzed by using an X-ray diffraction analysis and a field emission-scanning electron microscope, respectively. The relative dielectric permittivity and loss tangent were determined in the frequency range of 50 Hz to 1 MHz. For the $BaTiO_3/PVDF$ nanocomposites, the entire diffraction peaks match those indicated by standard $BaTiO_3$ perovskite structure. The FE-SEM image reveals the homogeneity of the $BaTiO_3$ nanopowder distribution and also predominant 0-3 connectivity. All results show that the dielectric properties of the nanocomposite films are desirable and the fabrication technique for preparing the $BaTiO_3/PVDF$ nanocomposites has a potential in the electronic applications.

• Korean Journal of Materials Research
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• v.5 no.7
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• pp.794-801
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• 1995

To connect the driver IC and Al coated glass, a method has been developed to plate electrolessly Ni on Al/PR system. It Is necessary to pretreat Al to remove oxide film before plating. In order to find pretreatment process which does not damage photoresist or glass, alkaline and fluoride zincate process have been investigated. Because photoresist and aluminum thin film can easily dissolve in alkaline solution, it is considered that the fluoride zincate process was a suitable one. After immersion in the zincate solution containing 1.5 g/$\ell$ ammonium bifluoride and 100 g/$\ell$ zinc sulfate, electroless nickel plating could be performed. The additive in the zincate solution and thiourea in the plating solution increased smoothness of the plated surface. Acld dip could improve the uniformit of the surface.

• The Journal of the Acoustical Society of Korea
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• v.42 no.5
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• pp.412-421
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• 2023

Ultrasound brain stimulation is spot-lighted by its capability of inducing brain cell activation in a localized deep brain region and ultimately treating impaired brain function while the efficiency and directivity of neural modulation are highly dependent on types of stimulus waveforms. Therefore, to optimize the types of stimulation parameters, we propose a cell-cultivable ultrasonic transducer having a series stack of a spin-coated polymer piezoelectric element (Poly-vinylidene fluoride-trifluorethylene, PVDF-TrFE) and a parylene insulating layer enhancing output acoustic pressure on a glass-coverslip which is commonly used in culturing cells. Due to the uniformity and high accuracy of stimulus waveform, tens of neuronal cell responses located on the transducer surface can be recorded simultaneously with fluorescence microscopy. By averaging the cell response traces from tens of cells, small changes to the low intensity ultrasound stimulations can be identified. In addition, the reduction of stimulus distortions made by standing wave generated from reflections between the transducers and other strong reflectors can be achieved by placing acoustic absorbers. Through the proposed ultrasound transducer, we could successfully observe the calcium responses induced by low-intensity ultrasound stimulation of 6 MHz, 0.2 MPa in astrocytes cultured on the transducer surface.

• Polymer(Korea)
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• v.37 no.1
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• pp.74-79
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• 2013

Polyvinylidene fluoride (PVDF) and its copolymer with hexafluoropropylene (HFP) were successfully prepared from free radical solution polymerizations using diisopropyl peroxidicarbonate (DIPPDC) in the presence of 1,1,2-trichlorotrifluoroethane (R-113). The reactivity ratios of VDF and HFP were estimated as$r_{VDF}=2.06{\pm}0.03$ and $r_{HFP}{\approx}0$. This result indicates that HFP cannot undergo self propagation. The weight-average molecular weight and molecular weight distribution of copolymers were found to decrease with increasing HFP content. The melting temperature of copolymers linearly decreased with the increase of HFP content because of the introduction of HFP. Moreover, no melting peak was observed for the copolymers with high HFP content. The glass transition temperature of copolymers gradually increased with the increase of HFP content due to the restricted flexibility of the polymer chains.

• Korean Journal of Materials Research
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• v.33 no.12
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• pp.517-524
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• 2023

BaTiO₃-Poly vinylidene fluoride (PVDF) solution was prepared by adding 0~25 wt% BaTiO₃ nanopowder and 10 wt% PVDF powder in solvent. BaTiO₃-PVDF film was fabricated by spreading the solution on a glass with a doctor blade. The output performance increased with increasing BaTiO₃ concentration. When the BaTiO₃ concentration was 20 wt%, the output voltage and current were 4.98 V and 1.03 ㎂ at an applied force of 100 N. However, they decreased when the over 20 wt% BaTiO₃ powder was added, due to the aggregation of particles. To enhance the output performance, the generator was poled with an electric field of 150~250 kV/cm at 100 ℃ for 12 h. The output performance increased with increasing electric field. The output voltage and current were 7.87 V and 2.5 ㎂ when poled with a 200 kV/cm electric field. This result seems likely to be caused by the c-axis alignment of the BaTiO₃ after poling treatment. XRD patterns of the poled BaTiO₃-PVDF films showed that the intensity of the (002) peak increased under high electric field. However, when the generator was poled with 250 kV/cm, the output performance of the generator degraded due to breakdown of the BaTiO₃-PVDF film. When the generator was matched with 800 Ω resistance, the power density of the generator reached 1.74 mW/m². The generator was able to charge a 10 ㎌ capacitor up to 1.11 V and turn on 10 red LEDs.