• Journal of the Korean Vacuum Society
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• v.9 no.3
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• pp.279-284
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• 2000

In order to analysis the degradation process of epoxy/glass fiber for outdoor condition, FRP laminate was exposed to high temperature and water. Then the degradation process was evaluated by comparing contact angle, surface potential decay, and surface resistivity. For the change of wettability, the contact angle of thermal-treated specimen with the high temperature of $200^{\circ}C$ increased. But that of water-treated specimen decreased. The characteristic of surface potential decay shows the tendency of the remarkable decrease on water-treated specimens, but increase on thermal-treated specimen compared with untreated one. Also, for the surface resistivity, it shows the same trend compared with the change of contact angle.

• Journal of the Korean Chemical Society
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• v.57 no.6
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• pp.691-696
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• 2013

Black carbon contributes to global warming and melting of polar ice as well as causing respiratory diseases. However, it is also an inexpensive, easily available carbon nano material for elementary chemistry experiments. In this study, black carbon samples collected from candle light and automobile exhaust pipes have been investigated to examine their compositions and surface characteristics. The observed broad G and D bands and amorphous $sp^3$ band in their Raman spectra as well as the high intensity of the D (defect) band reveal that black carbon is principally made of amorphous graphite. The black carbon deposits in automobile exhaust pipes are apparently more amorphous, probably due to the shorter time allowed for formation of the carbonaceous matter. An exceptionally large water contact angle ($159.7^{\circ}$) is observed on black carbon, confirming its superhydrophobicity. The surface roughness evidently plays an important role for the contact angle much larger than that of crystalline graphite ($98.3^{\circ}$). According to the Sassie-Baxter equation, less than 1% the area actually in contact with the water drop.

• Journal of the Korean Geosynthetics Society
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• v.21 no.4
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• pp.93-100
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• 2022

This study describes the evaluation results on the effect of soil particle surfaces coated with various hydrophobic conditions on spectral information according to water content. Wettability test and spectral information evaluation test were performed on the hydrophobic coated standard sand. When the standard sand was coated with 1%, 3%, and 5% hydrophobic, the contact angles of sand-water interface were 130°~143°, 129°~144°, and 131°~144°, respectively. This means that the contact angle increased as the degree of hydrophobic coating increased at the same drying time, but the range of the contact angle had the same wettability. This means that the contact angle increases as the hydrophobic coating degree increases at the same drying time, whereas the contact angle range has the same wettability. As a result of spectral information evaluation, the maximum spectral reflectance of the dried sand with hydrophobic condition decreased compared to that of the hydrophilic sand, as the degree of hydrophobic increased. However, the maximum spectral reflectance was increased by increasing the degree of hydrophobic under the same water content conditions.

• Journal of Adhesion and Interface
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• v.4 no.4
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• pp.1-6
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• 2003

After atmospheric pressure plasma treatment of polypropylene(PP) film surface, we measured the contact angle of the surface by using polar solvent (water) and non-polar solvent (diiodomethane). We also calculated the surface free energy of PP film by using the measured values of contact angles. And then we analyzed contact angle and surface free energy with changing the condition of atmospheric pressure plasma treatment. Upon each condition of atmospheric plasma treatment, contact angle and surface free energy showed an optimum value or leveled off.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.30 no.1
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• pp.33-43
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• 2018

This study numerically investigated statistic and dynamic behaviors of the water droplet on plate with or without various structured-pillars at nano-scale by molecular dynamics simulation. This study considered smooth plate, plate with the rectangular-structured pillar, and the plate with dual-structured pillar under various characteristic energy conditions. The static behavior of water droplet depending on the plate shape, plate surface energy, and the pillar characteristics were examined. After the water droplet reaches its steady state, this study investigated the dynamic behavior of the water droplet by applying a constant force. Finally, this study investigated the static and dynamic behaviors of the water droplet by measuring its contact angle and contact angle hysteresis. As a result, we found that the structure was more hydrophobic.

• Journal of the Korea Institute of Building Construction
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• v.21 no.6
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• pp.529-538
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• 2021

In this study, the compressive strength and water contact angle were measured before and after surface abrasion of mortar specimens prepared by mixing two types of water repellents and two types of sands. In addition, the hydration products and chemical bonding of cement mortar by repellent were examined using X-ray diffraction(XRD), thermogravimetry-differential thermal analysis(TG-DTA), and Fourier-transform infrared spectroscopy(FT-IR) to evaluate the performance of these cement mortar mixtures as repair materials. We found that the compressive strength of the cement mortar with water repellent added was decreased compared to that of the plain cement mortar, and that of the oligomeric system was higher than that of the monomeric system. We further found that the contact angle of mortar with water repellent added was increased compared to that of the plain cement mortar, and that of the oligomeric system was increased compared to that of the monomer.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.6 s.261
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• pp.679-685
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• 2007

Superhydrophobic surface, with a water contact angle greater than $150^{\circ}$, has a self-cleaning effect termed 'Lotus effect'. This surface is created by the combination of rough surface and the low surface energy. We proposed square pillar and square shapes to control surface roughness. Microstructure arrays are fabricated by DRIE(Deep Reactive Ion Etching) process and followed by PPFC(Plasma Polymerized Fluorocarbon) deposition. On the experimental result, contact angle at square pillar arrays is well matched with Cassie's model and largest contact angle is $173.37^{\circ}$. But contact angle of square pore shape arrays is lower than Cassie's theoretical contact angle about $5{\sim}10%$. Nevertheless, square pore arrays have more rigidity than square pillar arrays.

• Tribology and Lubricants
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• v.35 no.5
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• pp.294-299
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• 2019

Most previous studies on water repellent surfaces using lasers rely on the use of pico- or femtosecond lasers. However, in industrial application, these methods have the disadvantages of high cost and low efficiency. In this study, we implement a hydrophobic surface using a high-power general-purpose diode laser. We have fabricated the microsurface using laser groove processing technology, and we present the correlation of wettability characteristics with space and width. The metal material is stainless steel (SUS 304), and the groove height during laser processing is set to $30{\mu}m$ to evaluate the wettability based on the gap and width of various grooves. Results show that the contact angle of the groove-shaped surface is increased by $40^{\circ}$ or more as compared with the surface without patterning, and the contact angle in the parallel direction is greater than that in the perpendicular direction. Results from contact angle hysteresis measurement experiments show that the groove width has a greater influence on the contact angle history than does the gap between grooves. In addition, the coating reveals that the contact angle can be increased using a chemical method and that the laser grooving process can further improve the wetting properties of the surface.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.1
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• pp.95-101
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• 2000

The effect of surface contact angle on the behavior of frost formation in a fin-tube heat exchanger is investigated experimentally. It is shown that both heat exchangers with hydrophilic and hydrophobic surfaces appear to have a better thermal performance than bare aluminium heat exchanger, but the improvements are very small. There is a little increase in the amount of the frost deposited onto the heat exchanger with both hydrophilic and hydrophobic surface. However, the effect of contact angle on the frost density is observed ; the frost with high density forms on the heat exchanger with hydrophilic surface ; and the frost with low density is deposited onto the heat exchanger with hydrophobic surface when compared with the frost deposited onto the heat exchanger with bare aluminium surface. This may be attributed to the fact that the shape of water droplets which condense on the surface of heat exchanger at the early stage of frosting varies with contact angle, and thus makes a difference on the structure of frost formation. From the experiments with different relative humidity of inlet air, it is shown that the variations of operating parameter make no influence on the effect of surface contact angle on the frosting behavior in the heat exchanger.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.10
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• pp.553-558
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• 2000

This paper deals with change of contact angle, surface potential decay, surface resistivity and XPS of water-treated epoxy insulator. From the experimental results on the contact angle was reduced from $74^{\circ}$to $24^{\circ}$ due to the formation of polar hydroxyl groups on surface which was associated with intermolecular reaction between epoxy chains of three-dimensional network structure and water molecules. From the experimental results in the surface potential decay of water treated-samples, it was found that the accumulation of charge is decreased and the surface potential decay time is shortened by the interaction of polar hydroxyl groups induced on the treated surface as the increment of treatment time. The positive charging on the treated surface compared with negative charging is relatively lowered by the induction of polar hydroxyl groups. The surface resistivity was changed from $10^{15}[{\Omega}/cm^2$] to $10^{12}[{\Omega}/cm^2$] caused by water treatment. From XPS, it was found that the changes affected by the surface degradation of epoxy were caused by the generation of carboxyl groups through the chain decomposition and recombination with oxygen molecules in the air.