• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.35 no.3
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• pp.53-58
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• 2003

The newly developed system for measuring a contact angle on a sheet was examined to investigate reliability and reproducibility of the measured results. It was clearly confirmed that the automatic contact angle measuring system was much faster and more reliable way to determine the water resistance of a sheet, comparing with Cobb and Stockigt sizing tests. Cobb test showed less significant results with stringently sized sheets, and Stockigt test exhibited the big deviations by discrepancy of the recognition point of coloring according to different testers in spite of explicit test results. On the other hand, the contact angles measured by the automatic system were reproduced with less deviations, irrespectively of different testers. It was interesting to note that the contact angle might be able to used to predict Cobb and Stockigt sizing degree, based upon the high correlation coefficients of 0.95 and 0.97. Hereafter the automatic system will be upgraded to predict Cobb and stockigt sizing degree through the measurement of contact angle.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.662-665
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• 2008

We experimentally investigate the evaporation characteristics of water droplet on surfaces of various wettabilities in the range of contact angle from 30$^{circ}$ to 150$^{circ}$. When a liquid droplet on a solid surface evaporates, the contact angle generally decreases with time and the evaporation rate varies with the droplet geometry such as the contact angle and the radius of curvature. Experimental data on the contact angle as a function of the droplet volume obtained by digital image analysis techniques cannot be explained by the existing theories. By measuring the temporal evolutions of the droplet radius and contact angle, we find the qualitative difference between the evaporation patterns on the hydrophilic surfaces where the contact radius remains constant initially and those on the superhydrophobic surfaces where the contact angle remains constant. Also, the evaporation rate is observed to depend on the surface material although the currently available models assume that the rate is solely determined by the droplet geometry. Despite the fact that the theory to explain this dependence on the surface remains to be pursued by the future work, we give the empirical relations that can be used to predict the droplet volume evolution for each surface. It is expected that the present study will contribute to interpreting the effect of droplet geometry on the evaporation.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.2
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• pp.182-187
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• 2024

Currently, the most developed new energy source is solar energy. Because solar power is installed outside, it is exposed to many pollutants. Pollutants are causing the characteristics of solar energy to deteriorate. Therefore, this study aims to develop a water-repellent coating to prevent contamination of solar modules. Silica and Titania materials are mainly used as water-repellent coating materials. In this study, it was based on silica and the contact angle characteristics were measured according to the change in the amount of silica and ammonia water added and the number of coatings. As a result of the measurement, it was confirmed that the contact angle was more than 60 degrees when 0.5 mol of TEOS was added to 50 mL and 0.15 M when 1 mL of ammonia water was added to 296.47 ml of distilled water. And it was confirmed that the contact angle improved when the number of coatings was applied twice. A water-repellent coating material was applied to low iron tempered glass used to protect dye-sensitized solar cell modules. The characteristics of the module were measured after spraying DI-Water on low-emission tempered glass with a water-repellent coating. As a result of the measurement, the efficiency of the module without application, the efficiency of the module coated once, and the module coated twice were 4.87%, 4.90%, and 4.91%, respectively. It was confirmed that the efficiency of the module increased by applying water-repellent coating. As a result of this study, it is determined that the water-repellent coating material will help improve solar power generation efficiency and lifespan by being self-cleaning and non-reflective.

• Corrosion Science and Technology
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• v.15 no.4
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• pp.166-170
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• 2016

The combined process of porous type anodizing and desiccation treatment was applied to improve wettability of A1050 aluminum alloy. The water contact angles of anodized samples were increaseds considerably with desiccation treatment. However, there was no considerable effect of polishing and anodizing time on water contact angle. The corrosion behavior with the treatments was investigated electrochemically. The corrosion resistance of the samples in 3.5 mass% NaCl solutions increased with higher contact angle. Anodized and desiccated samples showed better corrosion resistance than un-desiccated samples around rest potential region.

• Tribology and Lubricants
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• v.33 no.6
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• pp.251-255
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• 2017

In this study, we aimed to clarify the wettability and anisotropic flow characteristics of rice leaves as a basic study for engineering applications of anisotropic flow characteristics of rice leaf surface. To investigate the surface structure of rice leaf, the micro grooves and asperities of rice leaves were analyzed and quantified by scanning electron microscope, Confocal laser scanning microscopy, and stylus profilometer. The analysis of the structure of rice leaf surface confirmed that asymmetrical cone - like protrusions in leaf veins were inclined toward the leaf tip. The static contact angle test showed that the contact angle at the midline vein or leaf vein location where the micropapilla is concentrated is about $20^{\circ}$ higher than the leaf blade position. The contact angles of fresh and dried rice leave were also compared. The dried rice leaves showed a contact angle of about $5^{\circ}$ to $15^{\circ}$ higher than that of fresh leaves, suggesting that the volume of the protrusions decreased as the water was removed, thus reducing the contact area with the droplet. In the contact angle history test the hysteresis in the leaf tip direction was found to be much lower than that in the leaf petiole direction. This results can be explained that asymmetrical cone - like protrusions had a significant effect on the droplet flow characteristics through contact angle hysteresis experiment.

• Textile Coloration and Finishing
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• v.10 no.5
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• pp.24-31
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• 1998

The effects of DMDHEU alone and DMDHEU/Fluorochemical(FC) combined treatment on the physical properties of 75％/25％ cotton/polyester(CP) blended fabrics were investigated. FC water repellent and DMDHEU durable press finishes were applied in combination to CP fabrics to provide good water repellency as well as great durable press(DP) performance. The physical properties of the fabrics were evaluated by wrinkle recovery angle(WRA), DP performance, contact angle, demand wettability, and water repellency. The durable press/water repellent finished(DP/WR) CP fabrics show considerably improved WRA and DP performance. The DP/WR finishes do not change the water contact angie of polyester fibers significantly, while the DP finishes increase it. Both DP and DP/WR finishes increase the contact angle of cotton fibers. The water uptake amount increases in the following order : DP/WR cotton, DP/WR CP＜DP cotton, DP CP ＜ Control CP, Control cotton. The water uptake amount increases in the following order DP/WR CP, DP/WR cotton ＜DP cotton ＜DP CP＜Control CP, Control cotton. Considerable improvements for water repellency are imparted to the CP fabrics treated with DP/WR, and the level of improvement is not significantly different from that of the DP/WR cotton fabrics. These results lead to the conclusion that DP/YVR treatments a single pad bath on CP are effective finishes for improving both DP performance and water repellency.

• Journal of the Korean Home Economics Association
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• v.35 no.3
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• pp.275-286
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• 1997

The effects of water-and oil-repellent finishes on the surface characteristics of polyester fabrics were investigated in this study. Three kinds of fluoropolyment were selected as water=and oil-repellent finishing agents. The effects of water-and oil-repellent finishes were determined by the water repellency and oil repellency. The surface properties of untreated and treated polyester fabrics were evaluated with respects to crease resistance, contact angle and wicking time. The results of this study were as follows: 1. The polyester fabrics treated with fluoropolymers showed much higher water repellency and oil repellency than those of untreated polyester fabrics. Water-and oil-repellency of fabrics were increased with the crystallinity and the hydrophobic-hydrophillic components of fluoropolymers. 2. Water repellency of fabrics treated with fluoropolymer with hydrophobic components was the highest. Oil repellency of fabrics treated with fluoropolymer with high crystallinity was the highest. Water-and oil-repellency of fabrics treated with fluoropolymer with hydrophyllic components was low comparatively. 3. The crease resistance of polyester fabrics treated with fluoropolymer nearly approached to that of untreated polyester fabric. 4. The water-and oil-repellent finishes improved contact angle markedly. Especially the contact angle of ployester fabric treated with fluropolymer with hydrophobic component was the biggest. 5. The wicking time of polyester fabric treated with fluropolymer with hydrophobic component was the longest.

• Journal of Biosystems Engineering
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• v.35 no.4
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• pp.257-261
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• 2010

Surface energy is the principal factor of anti-condensation. High surface energy appears hydrophilic itself and low surface energy represents hydrophobic itself. The contact angle is widely being used for measurement of surface energy of materials, evaluation of coating performances, measurement of wettability, and so on. However, the existing contact angle measuring system is so expensive for purchasing and complicated, so it takes a lot of time and money to use. This study was conducted to develop the algorithm for evaluating hydrophilic performance through measuring the contact angle of water droplet automatically, and fabricate relatively simple measuring system using a low-cost monochrome camera and image processing. A constant amount of water was firstly allocated on a slide by a micropipette, and then the image of water droplet was captured by monochrome digital camera and sent to a computer. The image was binarized and then reduced noises by labeling. Finally, the contact angle of water droplet was computed by using three points (left, right, and top coordinates), simple linear mathematics, and trigonometric function. The experimental results demonstrated the accuracy and reproducibility of the developed system showing less deviations and deviation ratio.

• Journal of the Korean Vacuum Society
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• v.19 no.1
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• pp.22-27
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• 2010

To improve surface wettability, each sample was treated by atmospheric pressure plasma (APP) using dielectric barrier discharge (DBD) system. Argon and oxygen gases were used for treatment gas to modify the $TiO_2$ surface by APP with RF power range from 50 to 200 W. Water contact angle was decreased from $20^{\circ}$ to $10^{\circ}$ with argon only. However, water contact angle was decreased from $20^{\circ}$ to < $1^{\circ}$ with mixture of argon and oxygen. Water contact angle with $O_2$ plasma was lower than water contact angle with Ar plasma at the same RF power. It seems to be increasing the polar force of $TiO_2$ surface. Also, analysis result of X-ray photoelectron spectra (XPS) shows the increase of intensity of O1s shoulder peak, resulting in increasing of surface wettability by APP. Moreover, each water contact angle increased according to increase past time. However, contact angle increase with plasma treatment was lower than without plasma treatment. Additionally, the efficiency of $TiO_2$ photocatalyst was improved by plasma surface-treatment through the degradation experiment of phenol.

• Proceedings of the KIEE Conference
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• 2001.11a
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• pp.6-8
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• 2001

This report describes the effect of the blending of poly(trifluoropropylmethylvinylsiloxane) (PTFPMVS) with poly(dimethylsiloxane) (PDMS) on the surface properties such as water repellency using dynamic contact angle (DCA) measurement. We have investigated the surface molecular mobility of the PDMS/PTFPMVS blends via a DCA measurement and an adhesion tension relaxation. It could be shown that a flexible side-chain segment in PTFPMVS having higher surface energy, could be reoriented easily in water to decrease the interfacial tension of the polymer/water interface, which seems to play a major role at the decrease of the receding contact angle and the surface resistivity of PDMS/PTFPMVS blends.