• Korean Journal of Materials Research
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• v.13 no.3
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• pp.185-190
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• 2003

Titanium dioxide films were prepared by RF sputtering method on glass for various oxygen partial pressures at power 270 W. The crystal structure, photocatalytic property and the hydrophilicity of $TiO_2$thin film the deposition conditions were investigated. Crystallized anatase phase was observed in $TiO_2$film deposited at the ratio of oxygen partial pressure 10% and 20% for 2 hrs. As the increase of deposition time, the grain size and void size of $TiO_2$film have increased and also $V_2$films have been good crystallinity. The ultraviolet-visible light absorption of $TiO_2$films was increased with increasing of deposition time and occured chiefly at the wavelength between 280 and 340 nm. The absorption band was shifted to a longer wave length as deposition time increased. Water contact angle on the X$TiO_2$film of anatase structure was decreased with increasing ultraviolet illumination time and became lower than $11^{\circ}$ from $83^{\circ}$. When hydrophilic $TiO_2$film changed by enough ultraviolet illumination was stored in the dark, the film surface gradually turned to hydrophobic state.

• Journal of the Korean institute of surface engineering
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• v.46 no.3
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• pp.105-110
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• 2013

ZnS thin films were prepared on glass substrate by using chemical bath deposition method. The influence of ammonia ($NH_4OH$) and $Na_2EDTA$ ($Na_2C_{10}H_{16}N_2O_8$) as complexing agents on structural and optical properties of ZnS thin films were investigated. Zinc acetate dihydrate ($Zn(CH_3COO)_2{\cdot}2H_2O$) and thiourea ($H_2NCSNH_2$) were used as a starting materials and distilled water was used as a solvent. All ZnS thin films, regardless of a kind of complexing agents, had the hexagonal structure (${\alpha}$-ZnS) and had a preferred <101> orientation. ZnS thin films, with 4 M ammonia and with 4 M ammonia and 0.1 M $Na_2EDTA$, had the highest <101> peak intensity. In addition, their average particle size are 280 nm and 220 nm, respectively. The average optical transmittances of all films were higher than 60% in the visible range. The optical direct band gap values of films were about 3.6~3.8 eV.

• Applied Chemistry for Engineering
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• v.2 no.4
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• pp.340-347
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• 1991

Siloxane containing copolyimide (SPI) was synthesized from 3, 3', 4, 4'-benzophenonetetracarboxylic dianhydride(BTDA), 4, 4'-methylene dianiline(MDA), 4, 4'-oxydianiline(ODA) and amine-terminated polydimethyl-siloxane(PDMS). Homopolyamic acid(HPAA) in tetrahydrofuran(THF) was reacted with PDMS to obtain siloxane containing polyamic acid(SPAA) followed by the thermal curing to manufacture SPI. SPAA and HPAA exhibited inherent viscosity value of 0.35~0.48dl/g. Glass transition temperature of SPI ranged in $258^{\circ}C{\sim}264^{\circ}C$. SPI had a lower $T_g$ than that of HPI. ODA based HPI and SPI showed slightly higher $T_g$ values, thermal stability, and water content.

• Korean Journal of Materials Research
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• v.22 no.9
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• pp.494-498
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• 2012

Geopolymer cements and geopolymer resins are newly advanced mineral binders that are used in order to reduce the carbon dioxide generation that accompanies cement production. The effect of additives on the compressive strength of geopolymerized class-F fly ash was investigated. Blast furnace slag, calcium hydroxide($Ca(OH)_2$), and silica fume powders were added to fly ash. A geopolymeric reaction was initiated by adding a solution of water glass and sodium hydroxide(NaOH) to the powder mixtures. The compressive strength of pure fly ash cured at room temperature for 28 days was found to be as low as 291 $kgf/cm^{-2}$, which was not a suitable value for use in engineering materials. On the contrary, addition of 20 wt% and 40 wt% of blast furnace slag powders to fly ash increased the compressive strength to 458 $kgf/cm^{-2}$ and 750 $kgf/cm^{-2}$, respectively. 5 wt% addition of $Ca(OH)_2$ increased the compressive strength up to 640 $kgf/cm^{-2}$; further addition of $Ca(OH)_2$ further increased the compressive strength. When 2 wt% of silica fume was added, the compressive strength increased to 577 $kgf/cm^{-2}$; the maximum strength was obtained at 6 wt% addition of silica fume. It was confirmed that the addition of CaO and $SiO_2$ to the fly ash powders was effective at increasing the compressive strength of geopolymerized fly ash.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.5
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• pp.533-551
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• 2015

The rock fracturing during waterjet cutting is very complicated because rock is inhomogeneous and anisotropic, compared with artificial materials (e.g., metal or glass). Thus, it is very important to verify the effects of rock properties on waterjet rock cutting performance. Properties affecting the rock cutting efficiency have been variously described in the literature, depending on the experimental conditions (e.g., water pressure, abrasive feed rate, or standoff distance) and rock-types studied. In this study, a rock-property-related literature review was performed to determine the key properties important for waterjet rock cutting. Porosity, uniaxial compressive strength, and hardness of the rock were determined to be the key properties affecting waterjet rock cutting. The results of this analysis can provide the basic knowledge to determine the cutting efficiency of waterjet rock cutting technology for rock excavation-related construction.

• Polymer(Korea)
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• v.30 no.3
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• pp.207-209
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• 2006

We fabricated a capacitive-type humidity sensor using poly (p-phenylene ether sulfone: PES) as a humidity sensitive layer. The PES was dissolved in m-cresol $(CH_3C_6H_4OH)$ and spin-coated on ITO-coated glass substrate. Gold was deposited by sputtering as a water-permeable upper electrode. The capacitance of the sensor was inversely proportional to sensing film thicknesses and showed an excellent linearity of less than 1% in the humidity range of 20 to 90%. The sensor haying a $1.4{\mu}m$ sensing layer showed a hysteresis of 1.3% and a good sensitivity of 1.14 at 20 kHz.

• The Journal of Advanced Prosthodontics
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• v.10 no.2
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• pp.101-112
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• 2018

PURPOSE. The purpose of this study was to investigate the effect of various surface treatments (ST) on the shear bond strength of resin composite to three bilayer dental ceramics made by CAD/CAM and two veneering ceramics. MATERIALS AND METHODS. Three different bilayer dental ceramics and two different veneering ceramics were used (Group A: IPS e.max CAD+IPS e.max Ceram; Group B: IPS e.max ZirCAD+IPS e.max Ceram, Group C: Vita Suprinity+Vita VM11; Group D: IPS e.max Ceram; Group E: Vita VM11). All groups were divided into eight subgroups according to the ST. Then, all test specimens were repaired with a nano hybrid resin composite. Half of the test specimens were subjected to thermocycling procedure and the other half was stored in distilled water at $37^{\circ}C$. Shear bond strength tests for all test specimens were carried out with a universal testing machine. RESULTS. There were statistically significant differences among the tested surface treatments within the all tested fracture types (P<.005). HF etching showed higher bond strength values in Groups A, C, D, and E than the other tested ST. However, bonding durability of all the surface-treated groups were similar after thermocycling (P>.00125). CONCLUSION. This study revealed that HF etching for glass ceramics and sandblasting for zirconia ceramics were adequate for repair of all ceramic restorations. The effect of ceramic type exposed on the fracture area was not significant on the repair bond strength of resin composites to different ceramic types.

• Journal of the Korean Applied Science and Technology
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• v.35 no.2
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• pp.502-508
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• 2018

The acrylate copolymer having good coating, water-repellent and adhesion properties was designed and prepared. We prepared copolymers with high yield of > 95% using methyl methacrylate(MMA), 2,2,2-trifluoroethyl acrylate (FMA) and 2-hydroxyethyl methacrylate monomers(HEMA) by either bulk or emulsion polymerization techniques. The $^1H-NMR$ spectrum was used to identify chemical structure and DSC and DMA analysis were conducted. As a result, the glass transition temperature decreased by $3^{\circ}C$ as FMA content increased from 5% to 10%, and decreased by $2{\sim}8^{\circ}C$ when HEMA content increased from 5 % to 10 %. The physical properties were measured using Instron and TGA. As FMA or HEMA content increased by 10%, tensile strength decreased from 29 MPa to 22 MPa and Td decreased from $200^{\circ}C$ to $180^{\circ}C$ in both bulk and emulsion. The contact angle relatively decreased as hydrophilic HEMA content increased.

• Journal of the Korean Society for Marine Environment & Energy
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• v.15 no.1
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• pp.47-53
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• 2012

As one of the methods for recycling the FRP from the waste ships, separation of roving layer from the mat has some merits in a sense of the eco-friendly and economical recycling process. Similar characteristics, however, between the roving and the mat even with different ratio of the resin and the glass and the thickness of the roving, much thinner than the mat, make the mechanically automatic differentiation difficult. In this study spectrochemical differentiation between the two layers has been made using boiling concentrated sulfuric acid, methanol and isopropanol solution saturated with KOH, or hydrogen fluoride (HF) solution. Furthermore efficiently coloring water-soluble dye following the HF treatment makes the roving layer more distinguishable photophysically. The layer differentiation and the automatic layer distraction move up the date of simple and automatic separation process for the waste FRP.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.335-335
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• 2011

Instability of a thin film attached to a compliant substrate often leads to emergence of exquisite wrinkle patterns with length scales that depend on the system geometry and applied stresses. However, the patterns that are created using the current techniques in polymer surface engineering, generally have low aspect ratio of undulation amplitude to wavelength, thus, limiting their application. Here, we present a novel and effective method that enables us to create wrinkles with a desired wavelength and high aspect ratio of amplitude over wavelength as large as to 2.5:1. First, we create buckle patterns with high aspect ratio of amplitude to wavelength by deposition of an amorphous carbon film on a surface of a soft polymer poly(dimethylsiloxane) (PDMS). Amorphous carbon films are used as a protective layer in structural systems and biomedical components, due to their low friction coefficient, strong wear resistance against, and high elastic modulus and hardness. The deposited carbon layer is generally under high residual compressive stresses (~1 GPa), making it susceptible to buckle delamination on a hard substrate (e.g. silicon or glass) and to wrinkle on a flexible or soft substrate. Then, we employ glancing angle deposition (GLAD) for deposition of a high aspect ratio patterns with amorphous carbon coating on a PDMS surface. Using this method, pattern amplitudes of several nm to submicron size can be achieved by varying the carbon deposition time, allowing us to harness patterned polymers substrates for variety of application. Specifically, we demonstrate a potential application of the high aspect wrinkles for changing the surface structures with low surface energy materials of amorphous carbon coatings, increasing the water wettability.