Earticle

In this study, infrared thermometry techniques were used to conduct surface wetting performance tests (wicking tests) on micropillar structures with good fluid supply capabilities to enhance the critical heat flux. Wicking tests were conducted based on various micropillar shapes (i.e., diameter and spacing) to investigate the surface wetting performance near the boiling point of the fluid(~100°C). The surface temperature was increased from 20°C to 95°C, to examine the wicking performance The shape of the micropillars were quantified by the roughness and the effect of the roughness and temperature on the wicking performance was analyzed. As a result, we confirmed that the roughness of the micropillars increases the capillary pressure, improving the wicking performance. The sample D04 G10 with the highest roughness coefficient at room temperature (r=2.51) exhibited the highest wicking coefficient, showing a 170% improvement in wicking performance compared to D04G20 with the smallest roughness coefficient at room temperature(r=1.51). Additionally, the D04 G10 sample (r=2.51) recorded a 50% improvement in the wicking coefficient at the highest temperature(95°C) compared to room temperature(20°C). The wicking coefficient data will be utilized as a database for developing a new correlation for critical heat flux.

Rainfall is a major external factor contributing to landslides. The development of a wetting front due to rainfall increases the self-weight of the soil mass and reduces the negative pore water pressure, ultimately leading to a decrease in shear strength along the slope. Therefore, accurately estimating the depth and amount of infiltration associated with rainfall is crucial for predicting landslides. Although numerous studies have been conducted to predict the movement of the wetting front and the corresponding changes in soil water content during rainfall infiltration, many of these studies assume vertical piston flow, which leads to discrepancies from actual field behavior. In reality, a transition zone exists within the wetting front, and infiltration progresses in an unsaturated state without complete saturation. In this study, it was confirmed that the transition zone within the wetting front follows a Sigmoid-shaped profile. Based on this observation, a rainfall infiltration model was developed that incorporates both unsaturated conditions and the transitional behavior of the wetting front. The proposed model was applied to infinite slope analysis under unsaturated conditions, and its results were compared with those from conventional theoretical approaches. As a result, the proposed model demonstrated improved accuracy in predicting the wetting front and effectively captured the unsaturated and transitional characteristics of the infiltration process. Furthermore, compared to existing models, the safety factor of slopes was found to be relatively higher, with a gradual variation in safety factor observed due to the influence of the transition zone.

Generally, in the previous researches, it is found that a water droplet is respectively in Wenzel and Cassie-Baxter states on hydrophilic/hydrophobic rough surfaces. And Wenzel and Cassie-Baxter equations are used to estimate the apparent contact angle on the surfaces. However, difference between measured apparent contact angle and estimated apparent contact angle with the equations is recently reported and new model to estimate apparent contact angle on rough surfaces is proposed. In this study, wetting state and apparent contact angle on the surfaces with micro-pillars should be investigated to find solution of this argument. Using the high resolution microscope, the wetting state of the D.I.water droplet on the surface with micro-pillars was visualized and apparent contact angle of the D.I.water droplet was measured. On the basis of experimental data, the equations to estimate apparent contact angle were verificated and the general wetting characteristics on the surfaces with micro-pillars are finally classified.

The oscillation in the entropy change at the NI(nematic-isotropic) phase transition temperature becomes less distinct when the linking group is replaced by the carbonate. In our previous work, we have suggested that such characteristics arise from the geometrical arrangement of the linkage. In this work, deuterium NMR studies have been carrier out for a series of carbonate-type dimer liquid crystals MCOC(O)O(CH2)OC(O)CN(CBC-c, c=5.6) to elucidate the conformational characteristics of the spacer in the nematic phase. The H-NMR spectra were recorded on a JEOL GSX-500 apparatus by using deuterium labelled CBC-n. Following the previous treatment, the single-ordering-matrix model was adopted, in which the molecular axis was defined along the line connecting the centers of the terminal mesogenic cores. Conformer fractions were estimated by simulation so as to reproduce the observed NMR profile. Under a nematic constraint the conformers should be restricted to a certain portion of all the allowed conformations of the spacer in the free stats. Hence the calculations were carried out for an ensemble of conformer having the angle between the mesogenic core and the molecular axis smaller than a certain valur Successful results were as follows:

연구목적: 본 연구에서는 석탄 심부 화재 발생 시 대응과 침윤소화약제의 실효성 확대를 위한 기술기준 개선방안을 제시하고자 하였다. 연구방법: 석탄 8톤과 침윤소화약제 3종, 소화용수를 활용하여 침투 실 험을 수행하고, 국내⋅외 기술기준 및 해외 사례를 분석하였다. 연구결과: 소화용수는 높은 표면장력으 로 인해 석탄 심부로 침투하지 못하였고, 침윤소화약제는 5~25cm 깊이까지 침투되었다. 국내 기술기준 은 침투성에 대한 간접 측정 방식인 표면장력만 언급되어있고, 소화능력시험도 목재를 활용하는 것으 로 확인되었다. 반면 해외에서는 면직물을 활용한 심부 화재 실험, 헵탄을 이용한 B급 화재 실험이 있는 것을 확인하였다. 그 외, 미 광산국에서는 모세관 상승 시험, 침전시험, 접촉각 측정이 있는 것으로 분석 되었다. 결론: 미국 NFPA 및 광산국의 기준과 사례를 토대로 국내 기술기준도 침투성을 직접적으로 측 정할 수 있는 기준을 추가하여 실효성을 확대할 필요가 있을 것으로 사료된다.

Purpose: This study is about offering ways of improving existing technical standards in order to propose how to deal with coal deep-seated fire and to increase effectiveness of wetting agent. Method: This study conducts infiltration experiment using eight tons of coal, three types of wetting agents and fire water. And this study analyzes domestic and international technical standards, overseas experimental cases. Result: It is found that two findings are identified; one is fire water cannot infiltrate into the coal due to high level of surface tension, and the other is three types of wetting agent can infiltrate into the coal to the depth of 5~25cm. Also, domestic wetting agent technical standards include measuring surface tension only and testing wood on extinguishing capacity test. On the other hand, this study found that deep-seated fire experiment using cotton, B-class fire test using heptane are used from abroad. Besides it is analyze that capillary rise test, sink test, contact angle measurement are conducted to increase effectiveness of wetting agent at the U.S. Bureau of Mines. Conclusion: Based on standards and cases of U.S. NFPA and Bureau of Mines, this study suggests that domestic technical standards should include adding a new test standard which measures infiltration directly.

Ultra-thin liquid films on solid substrates in contact with the saturated vapor are studied by using molecular dynamics simulation. The properties of evaporation and condensation of the films of various adsorptive strengths and thicknesses are obtained during the quasi-steady film evolution. Net condensations occur when the ultra-thin films on the high energy surface come into contact with the saturated vapor phase because the normal film pressure stays lower than the saturated vapor pressure. The net condensation rate is higher for the material combination of higher adsorptive strength. It becomes more so when the film thickness is of a lesser size. On the other hand, that of lower adsorptive strength has lower net condensation rate and depends less on the film thickness. Therefore, the size effect of the condensation phenomenon is more significant for the system of a higher adsorptive strength. This properties come from the state of ultra- thin film, which can be quantified by using disjoining pressure in the quasi-steady processes. These results have implications in practical problems concerning the moving contact line when the precursor film formation is critical.

Water resistance of three biopolyester films, such as poly-L-lactate (PLA), poly-hydroxybutyrate-co-valerate (PHBV), and Ecoflex, and low density polyethylene (LDPE) film was investigated by measuring contact angle of various probe liquids on the films. The properties measured were initial contact angle of water, dynamic change of the water contact angle with time, and the critical surface energy of the films. Water contact angle of the biopolyester films (57.62-68.76) was lower than that of LDPE film (85.19) indicating biopolyester films are less hydrophobic. The result of dynamic change of water contact angle also showed that the biopolyester films are less water resistant than LDPE film, but much more water resistant than cellulose-based packaging materials. Apparent critical surface energy for the biopolyester films (35.15-38.55 mN/m) was higher than that of LDPE film (28.59 mN/m) indicating LDPE film is more hydrophobic.

의심문서에 유류된 잠재지문을 안정적으로 현출할 수 있는 새로운 불소계(CFs) 화합물을 탐색 하고자, 습윤지수(WI)에 관한 정량적인 구조와 물리-화학적인 성질과의 관계를 설명하는 최적화 된 QSPR 모델 No.5 (R2= 0.90)를 유도하고 FC-72 용매를 예측하였다. 그리고 유류된 잠재지문 중 아미노산에 대하여 Ninhydrin 방법보다 민감한 Dansyl 방법으로 acetone, HFE-7100 및 예측된 FC-72 등 3가 지 용매중에서 잠재지문 현출실험을 실행하였다. 또한, 용매분자의 소수성(logP)과 습윤지수(WI) 사이 에 성립하는 유의미한 비례관계로부터 실습윤지수의 86% (100*R2)를 설명할 수 있는 유용한 모델 No. 4를 얻었다. 그러므로 용매들의 소수성(logP)에 관한 모델 No. 4에 근거하여 최적화 된 QSPR 모델 No. 5는 불소계(CFs) 지문현출 용매를 탐색하는 목적으로 효과적인 수단이 될 수 있을 것이다. Dansyl 방법에 의한 지문현출 결과로부터 예측된 FC-72 용매는 HFE-7100 용매에 비하여 양호하였으며 특히, 액상 현출제임에도 불구하고 비다공성 재질에서 양호한 현출성을 나타내었다.

To search new fluorine family (CFs) compounds as carrier solvent that can stably detecting from the latent fingerprint deposited on the suspicious document in the forensic science, the optimized QSPR (Quantitative structure -property relationship) model No. 5 (R=0.90) on Wetting index (WI) was derived and predicted the FC-72 solvent. And latent fingerprint detection experiments were carried out in three carrier solvents, acetone, HFE-7100 and predicted FC-72 by Dansyl method. This method is more sensitive than Nihydrin method to amino acids in deposited latent fingerprints. Also, useful the model No.4 that can explain 86% (100*R2) of real wetting index from the meaningful proportional relationships between hydrophobicity (logP) of solvents and wetting index (WI) was obtained. Therefore, based on the Model No.5 for hyrophobicity of solvents, the optimized QSPR model No.5 would be able to an effective way in searching of fluorine family (CFs) fingerprint detection solvents. From the results of fingerprint detection by Dansyl method, it was found that the predicted solvent FC-72 was more effective as compared to HFE-7100 solvent. Particularly, it shows very good detection rate on the nonporous materials even though FC-72 solvent is liquid phase detection agent.

Recently, there has been a continuous researches on solders having sophisticated and improved performance due to demand for high-density and miniaturization of electronics, and development of solder for automotive electronics which can be used in harsh environment. When developing a new solder alloy, there is a wettability of solder on substrate for things to consider, and the wetting balance test is one of the methods for measuring that one. In this paper, the wetting balance test is introduced, and the calculus of the surface tension of solder and the contact angle between solder and substrate using wetting curve obtained is introduced too. In detail, the principle and test method of the wetting balance test, the introduction of the parameters with important meaning in the wetting curve, the method of calculating the contact angle as well as the surface tension of the solder using the shape of the solder meniscus.

Recently, the high speed railway comes into the spotlight as the important and convenient traffic infrastructure. In Korea, Kyung-Bu high speed train service began in about 400km section at 2004, and the Ho-Nam high speed railway will be constructed by 2017. The high speed train will run with a design maximum speed of 300-350km/hr. Since the trains are operated at high speed, the differential settlement of subgrade under the rail is able to cause a fatal disaster. Therefore, the differential settlement of the embankment must be controlled with the greatest care. Furthermore, the characteristics and causes of settlements which occurred under construction and post-construction should be investigated. A considerable number of studies have been conducted on the settlement of the natural ground over the past several decades. But little attention has been given to the compression settlement of the embankment. The long-term settlement of compacted fills embankments is greatly influenced by the post-construction wetting. This is called 'hydro collapse' or 'wetting collapse'. In spite of little study for this wetting collapse problem, it has been recognized that the compressibility of compacted sands, gravels and rockfills exhibit low compressibility at low pressures, but there can be significant compression at high pressures due to grain crushing by several researchers(Marachi et al. 1969, Nobari and Duncan 1972, Noorany et al. 1994, Houston et al. 1993, Wu 2004). The characteristics of compression of fill materials depend on a number of factors such as soil/rock type, as-compacted moisture, density, stress level and wetting condition. Because of the complexity of these factors, it is not easy to predict quantitatively the amount of compression without extensive tests. Therefore, in this research I carried out the wetting collapse tests, with focusing in various soil/rock type, stress levels, wetting condition more closely.

Pt nanotubes with diameter of 200 nm were fabricated by simple and convenient method of Template-Wetting Process. Porous alumina membranes were prepared by 2 step anodic oxidation as the template. To improve wetting properties and lower surface energy, pt solution was mixed with polymer. Polymer was removed completely during annealing. Grain growth process of pt nanotubes during baking and furnace annealing was examined by FE-SEM and XRD.

This study presents a molecular simulation of adhesion control between carbon nanotube (CNT) and Ag thin film deposited on silicon substrate. Rough and flat Ag thin film models were prepared to investigate the effect of surface roughness on adhesion force. Heat treatment was applied to the models to modify the adhesion characteristics of the Ag/CNT interface based on thermal wetting. Simulation results showed that the heat treatment altered the Ag thin film morphology by thermal wetting, causing an increase in contact area of Ag/CNT interface and the adhesion force for both the flat and rough models changed. Despite the increase in contact area, the adhesion force of flat Ag/CNT interface decreased after the heat treatment because of plastic deformation of the Ag thin film. The result suggests that internal stress of the CNT induced by the substrate deformation contributes in reduction of adhesion. Contrarily, heat treatment to the rough model increases adhesion force because of the expanded contact area. The contact area is speculated to be more influential to the adhesion force rather than the internal stress of the CNT on the rough Ag thin film, because the CNT on the rough model contains internal stress regardless of the heat treatment. Therefore, as demonstrated by simulation results, the heat treatment can prevent delamination or wear of CNT coating on a rough metallic substrate by thermal wetting phenomena.

This article discusses about the droplet movement on the super-hydrophobic surface by the electro-wetting on dielectric and the effect of particles on the contact angle as well as the movement is investigated. The movement of droplet, driven by the principle of electro-wetting on dielectric, and the effect of particles are experimentally verified according to the driving voltage and different particles concentrations (fluorescent, charged particles). To increase the contact angle, the super-hydrophobic surface is fabricated and applied to the dielectric layer for the EWOD device. Then its performance is verified and discussed.

세라믹 방열 복합체의 특성 비교를 위해 casting method로 제작하였으며, 이들의 광학적 이미지와 단면 FE-SEM 분석을 실시하였다. 각각의 복합체의 열전도성 특성을 비교 분석하였으며, silicon carbide(SiC)의 분산도 문제를 해결하기 위해 wetting process를 도입하여 SiC/epoxy 복합체를 제작하였다. 기존의 방법에서 발견된 복합체 내공극과 분산도 문제가 wetting process를 통해 향상되었으며, 충전제 함량에 따른 열전도성 특성을 분석하였다. SiC 복합체의 함량에 따른 공극률 해석을 통해 70 wt% SiC 복합체에서 가장 높은 열전도도 값을 보였으며, 이들의 단면 FE-SEM 분석을 통해 복합체 내의 충전제 분산도를 확인하였다.

Various kinds of thermal conductive ceramic/polymer composites (aluminum nitride, aluminum oxide, boron nitride, and silicon carbide/epoxy) were prepared by a casting method and their optical images were observed by FE-SEM. Among these, SiC/epoxy composite shows inhomogeneous dispersion features of SiC and air voids in the epoxy matrix layer, resulting in undesirable thermal conductive properties. To enhance the thermal conductivities of SiC/epoxy composites, the epoxy wetting method which can directly infiltrate the epoxy droplet onto filtrated SiC cake was employed to fabricate the homogeneously dispersed SiC/epoxy composite for ideal thermal conductive behavior, with maximum thermal conductivity of 3.85W/mK at 70 wt% of SiC filler contents.

Wetting agent is a substance that reduces the soil water repellency and causes a liquid to spread more easily into the soil. Wetting agents are well known as to improve irrigation efficiency. Phosphorus is one of the 17 essential nutrient elements and promote faster seed germination. The objective of this study was to evaluate wetting agent and P rates for fast germination and establishment of Kentucky bluegrass. Three levels of wetting agent which were 0.23, 0.46, and $0.92ml\;m^{-2}$ were applied and the P treatments were 5, 10, and $15g\;m^{-2}$. The medium and high rate of wetting agent at the high P rate had the greatest turfgrass coverage and took 28 days to reach 50% turfgrass coverage regardless of P application. Based on this study, wetting agent is effective for fast germination and establishment of Kentucky bluegrass if sufficient phosphorus is applied.

Wetting properties between silver-copper-titanium braze alloys with different titanium contents up to 2.8 mass% and hexagonal boron nitride ceramics were investigated using sessile drop method at 1123K in Argon. The final contact angle is less than $30^{\circ}$ when the Ti content was over 0.41 mass%. Meanwhile, the contact angle curves show different behavior. In case of using braze alloy containing 2.8 mass% of titanium, the initial contact angle is acute angle just after the melting of braze. In case of brazes containing titanium less than 2.26 mass%, the contact angle is larger than $90^{\circ}$ at the beginning and slowly decreases to acute angle. The reaction layer of titanium nitride is observed at the interface. In addition, the reaction of Ti in the braze and N in the bulk h-BN seemed to show diffusion limited spreading.

The use of dolomite refractories has increased during the past several years in the manufacturing of clean steel during the stainless steelmaking process. However, at the same time, the use of dolomite refractories has led to what is known as the skull formation. In the present work, to understand the skull formation, the wetting characteristics of dolomite substrates by liquid Fe-19wt%Cr-10wt%Ni alloys in various oxygen partial pressures were initially investigated at 1753K using the sessile drop technique. For comparison, the wetting characteristics of alumina substrates were investigated with the same technique. It was found that the wetting index, (1+$cos{\theta}$), of dolomite is approximately 40% higher compared to those of alumina. In addition, the oxygen partial pressure to generate the surface oxide, which may capture the liquid metal on the refractory surface, for dolomite is much lower than that for alumina. From this study, it was concluded that the use of dolomite is much more closely associated with the skull formation compared to the use of alumina due to the stronger wettability and the surface oxide formation at a lower oxygen partial pressure of dolomite.

The reliability of the solder joint is affected by type and extent of the interfacial reaction between solder and substrates. Therefore, understanding of intermetallic compounds produced by soldering in electronic packaging is essential. In-based alloys have been favored bonding devices that demand low soldering temperatures. For photonic and fiber optics packaging, m-based solders have become increasingly attractive as a soldering material candidate due to its ductility. In the present work, the interfacial reactions between indium solder and bare Cu Substrate are investigated. For the identification of intermetallic compounds, both Scanning Electron Microscopy(SEM) and X-Ray Diffraction(XRD) were employed. Experimental results showed that the intermetallic compounds, such as Cu$_{11}$In$_{9}$ was observed for bare Cu substrate. Additionally, the growth rate of these intermetallic compounds was increased with the reaction temperature and time. We found that the growth of the intermetallic compound follows the parabolic law, which indicates that the growth is diffusion-controlled.d.