• Journal of the Korean Society for Precision Engineering
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• v.29 no.9
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• pp.1020-1025
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• 2012

In this study, we fabricated the superhydrophobic and super-water-repellent surface with the micro/nano scale structures using simple conventional silicon wet-etching technique and the black silicon method by deep reactive ion etching. These fabrication methods are simple but very effective. Also we reported the droplet impact experimental results on the micro/nano-scaled surface. There are two representative impact behaviors as "rebound" and "fragmentation". We found the transition Weber number between "rebound" and "fragmentation" statements, experimentally. Additionally, we concerned about the dimensionless spreading diameters for our super-water-repellent surface. The novel characterization method was introduced for analysis including the "fragmentation" region. As a result, our super-water-repellent surface with the micro/nano-scaled structures shows the different impact behaviors compared with a reference smooth surface, by some meaningful experiments.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.224-224
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• 2012

For decades, carbon fiber has expanded their application fields from reinforced composites to energy storage and transfer technologies such as electrodes for super-capacitors and lithium ion batteries and gas diffusion layers for proton exchange membrane fuel cell. Especially in fuel cell, water repellency of gas diffusion layer has become very important property for preventing flooding which is induced by condensed water could damage the fuel cell performance. In this work, we fabricated superhydrophobic network of carbon fiber with high aspect ratio hair-like nanostructure by preferential oxygen plasma etching. Superhydrophobic carbon fiber surfaces were achieved by hydrophobic material coating with a siloxane-based hydrocarbon film, which increased the water contact angle from $147^{\circ}$ to $163^{\circ}$ and decreased the contact angle hysteresis from $71^{\circ}$ to below $5^{\circ}$, sufficient to cause droplet roll-off from the surface in millimeter scale water droplet deposition test. Also, we have explored that the condensation behavior (nucleation and growth) of water droplet on the superhydrophobic carbon fiber were significantly retarded due to the high-aspect-ratio nanostructures under super-saturated vapor conditions. It is implied that superhydrophobic carbon fiber can provide a passage for vapor or gas flow in wet environments such as a gas diffusion layer requiring the effective water removal in the operation of proton exchange membrane fuel cell. Moreover, such nanostructuring of carbon-based materials can be extended to carbon fiber, carbon black or carbon films for applications as a cathode in lithium batteries or carbon fiber composites.

• Structural Engineering and Mechanics
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• v.86 no.1
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• pp.109-118
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• 2023

Any place where exercise is common, such as a club, sports hall, or school, is considered a place for teaching sports. When doing sports, a very safe environment for sports should be chosen. The athlete should consider the safety of sports facilities and equipment, and if there is a defect, he should refrain from exercising in these places. The safety of sports facilities is very effective in creating people's sports activities, with the benefits of staying away from physical harm, enjoying sports, and having mental peace. Everyone has the right to participate in sports and recreation and to ensure that they enjoy a safe environment. The ability to manage and solve issues that may arise plays the most critical role in creating a safe environment. The quality of construction materials used for the construction of sports facilities is of great importance. In this work, the resistance and water repellency of concrete constituents for the construction of sports buildings have been investigated by nanoscience. Nano-concrete material solves the main problem of concrete surfaces, i.e., the entry of water and humidity into the structure. It also gives it a self-cleaning ability with its water repellency. Nanoparticles are placed between pores and cover the cracks, which causes roughness in the surface structure of concrete. The high roughness of the surface of the coated concrete caused its super-hydrophobicity. In hydrophobic surfaces, the higher the contact angle, the more hydrophobic the surface will be. In order to investigate the hydrophobic properties, silica nanoparticles, silica nanoparticles, and fly ash were prepared on concrete, and their properties were analyzed.

• Journal of the Korean Applied Science and Technology
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• v.36 no.2
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• pp.531-540
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• 2019

Hydrophilic and hydrophobic nanosilica and tetraethyl orthosilicate (TEOS) as a coupling agent was used to form a coarse spike structure as well as an excellent reactive hydroxyl groups on the glass surface. Then, a second treatment was carried out using a trichloro-(1H,1H,2H,2H)perfluorooctylsilane(TPFOS) solution for ultimate water repellent glass surface formation. The formation of hydrophobic coating layer on glass surface using silica aerosol, which is hydrophobic nanosilica, was not able to form a durable hydrophobic coating layer due to the absence of reactive -OH groups on the surface of nanosilica. On the other hand, a glass surface was first coated with a coating liquid prepared with hydrophilic hydroxyl group-containing nanosilica and hydrolyzed TEOS, and then coated with a TPFOS solution to introduce a hydrophobic surface on glass having a water contact angle of $150^{\circ}$ or more. The sliding angle of the coated glass was less than $1^{\circ}$, which meant the surface had a super water-repellent property. In addition, as the content of hydrophilic nanosilica increased, the optical transmittance decreased and the optical transmittance also decreased after 2nd coating with the TPFOS solution. The super-hydrophobic property of the coated glass was remained up to 50 times of rubbing durability test, but only hydrophobic property was shown after 200 times of rubbing durability test. Conclusively, the optimal coating conditions was double 1st coatings with the HP3 coating solution having a hydrophilic nanosilica content of 0.3 g, and subsequent 2nd coating with the TPFOS solution. It is believed that the coating solution thus prepared can be used as a surface treatment agent for solar cells where light transmittance is also important.

• Korean Chemical Engineering Research
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• v.57 no.2
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• pp.177-184
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• 2019

Non-fluorinated water repellent coating solutions were obtained using methyltrimethoxysilane (MTMS) and trimethylethoxysilane (TMES) as precursors. The solutions were spin-coated on a cold-rolled steel sheet and cured thermally to prepare water repellent coating films. During this process, the effect of molar ratio of TMES/MTMS was studied for the hydrophobic properties of the coating films. Hydrophobic properties of coating films were characterized using contact angle measurement, surface morphology analysis and infrared spectroscopy. When the molar ratio of TMES/MTMS was varied from 0 to 30, the contact angle of the un-coated cold-rolled steel sheet was $30^{\circ}$, whereas when the molar ratio of TMES/MTMS was 1, the contact angle increased to $104^{\circ}$ and water repellency was significantly improved. In the case of TMES/MTMS molar ratios of 10, 15, 25 and 30, the contact angles of coating films showed $109^{\circ}$, $114^{\circ}$, $117^{\circ}$ and $144^{\circ}$, respectively. At this time, the hydrophobicity of the coating films was improved by the increase of the surface roughness and the content of the methyl component at the coating surface. In particular, when the molar ratio of TMES/MTMS was 30, the overall surface roughness was greatly increased due to the presence of surface particles as well as the water repellency due to methyl groups of TMES, resulting in super hydrophobicity of $144^{\circ}$.

• Applied Microscopy
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• v.42 no.2
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• pp.95-103
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• 2012

The cell surface sculpture of the plant epidermis has received great interest recently. It has also been an active area of research, as the biological microstructures of the surface, such as papillae and waxes, exhibit several unique properties, including self-cleaning character; namely the "Lotus effect" first described in the leaves of the lotus, Nelumbo nucifera. The Lotus effect is the phenomenon in which the super-hydrophobic and water-repellent nature of lotus leaves allow water drops to run off easily on the surface in a rolling and sliding motion thereby facilitating the removal of dirt particles. It is well-known that surface roughness on the micro- and nanoscale is a primary characteristic allowing for the Lotus effect. This effect is common among plants and is of great technological importance, since it can be applied industrially in numerous fields. In the present study, Nelumbo nucifera leaf and stem epidermal surfaces have been examined with a focus on the features of papillae and wax crystalloids. Both young and mature Nelumbo nucifera leaf epidermis demonstrated the Lotus effect on their entire epidermal surface. The central area of the upper epidermis, in particular, formed extremely papillose surfaces, with an additional wax layer, enabling greater water repellency. Despite the presence of wax crystalloids, epidermal surfaces of the lower leaf and stem lacking papillae, were much more easily wetted.

• Journal of the Korean Applied Science and Technology
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• v.34 no.1
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• pp.66-82
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• 2017

Organosilicone-based surfactants consist of hydrophobic organosilicone groups coupled to hydrophilic polar groups. Organosilicone surfactants have been widely used in many industrial fields starting from polyurethane foam to construction materials, cosmetics, paints & inks, agrochemicals, etc., because of their low surface tension, lubricity, spreading, water repellency and thermal and chemical stability, resulted from the unique properties of organosilicone. Especially, trisiloxane surfactants, having low molecular weight organosilicone as hydrophobe, exhibit low surface tension and excellent wettability and spreadability, leading to their applications as super wetter/super spreader, but have the disadvantage of vulnerability to hydrolysis. A variety of trisiloxane surfactant structures are required to provide the functional improvement and the defect resolution for reflecting the necessities in the various applications. This review covers the synthetic schemes of reactive trisiloxanes as hydrophobic siloxane backbones, the main reaction schemes, such as hydrosilylation reaction, for coupling reactive trisiloxanes to hydrophilic groups, and the synthetic schemes of the main trisiloxane surfactants including polyether-, carbohydrate-, gemini-, bolaform-, double trisiloxane-type surfactants.

• Journal of the Korean Applied Science and Technology
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• v.34 no.3
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• pp.461-477
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• 2017

Organosilicone-based surfactants, consisting of hydrophobic organosilicone groups coupled to hydrophilic polar groups, have been widely used in many industrial fields starting from polyurethane foam to construction materials, cosmetics, paints & inks, agrochemicals, etc., because of their low surface tension, lubricity, spreading, water repellency and thermal and chemical stability, resulted from the unique properties of organosilicone. Especially, organosiloxane surfactants, having low molecular weight siloxane as hydrophobe, exhibit low surface tension and excellent wettability and spreadability, leading to their applications as super wetter/super spreader, but have the disadvantage of vulnerability to hydrolysis. A variety of low molecular weight siloxane surfactant structures are required to provide the functional improvement and the defect resolution for reflecting the necessities in the various applications. This review includes the synthetic schemes of reactive tetrasiloxanes and disiloxanes as hydrophobic siloxane backbones, the main reaction schemes, such as hydrosilylation reaction, for coupling reactive tetrasiloxanes or disiloxanes to hydrophilic groups, and the main synthetic schemes of the tetra- and di-siloxane surfactants having polyether-, carbohydrate-, gemini-, bola-type surfactant structures.