• Tribology and Lubricants
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• 제37권1호
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• pp.1-6
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• 2021

This paper presents the experimental results of hydrophobic surfaces developed using a stereolithography-based additive-manufacturing technique. The additive manufacturing technique can be used to manufacture objects with complex geometries from computer-aided design data. Several additive manufacturing methods, such as selective laser sintering, fused deposition modeling, stereolithography apparatus (SLA), and inkjet-based system, have been developed. The SLA is a form of three-dimensional printing technology used to create prototypes, patterns, and production parts in successive layers through photochemical processes. Light causes chemical monomers and oligomers to cross-link together to form objects composed of polymers. Moreover, this method is economical for fabricating surfaces with high output resolution and quality. Here, we fabricate various surfaces using different shapes using an SLA. The surfaces with micro-patterns are fabricated for 10 cases, including the biomimetic surface. The fabricated surfaces with various micro-patterns are evaluated for hydrophobicity performance based on the static contact angle. The contact angle is measured three times for each case, and the averaged value is used. The results indicate that the arrangements in a staggered structure have a larger contact angle than those in a line when the same micro-pattern is applied. Moreover, the mimetic surfaces exhibit more hydrophobic characteristics than those of artificial micro-patterns.

• Tribology and Lubricants
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• 제20권5호
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• pp.237-244
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• 2004

Micro/nano tribological characteristics of PTFE coating films were experimentally studied. PTFE (polytetrafluoroethylene) modified polyethylene and low molecular weight PTFE were used as a coating materials. These films were deposited on Si-wafer (100) by IBAD (ion beam assisted deposition) method. The Ar ion beam sputtering was performed to change the surface topography of films using a hollow cathode ion gun under different Ar ion dose conditions in a vacuum chamber. Micro/nano tribological characteristics, water wetting angles and roughness were measured with a micro tribotester, SPM (scanning probe microscope), contact anglemeter and profilometer, respectively. The durability of the films were measured with macro tribotester. Results showed that the PTFE coating surfaces were converted to hydrophobic. The water contact angle of coated surfaces and surface roughness increased with the coating thickness. Adhesion and friction in micro and nano scale were governed by magnitude of normal load in soft material such as PTFE films. As the increase of sputtering time on low molecular weight PTFE films, the surface roughness was increased and nano adhesion and friction were decreased. The nano tribological characteristics of surfaces are mainly improved by chemical modification such as PTFE coating and given a synergy effect by the physical modification such as topographic modification.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.255-256
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• 2002

In this paper, the frictional behavior according to the contact geometry was investigated using a micro-tribotester built inside a Scanning Electron Microscope (SEM) and an Atomic Force Microscope (AFM). FFT (Fast Fourier Transform) analysis for friction was conducted as a method to interpret the contact condition. From the experimental results, it could be concluded that the relative dimensions and distribution of contact asperities on the surface could be predicted by the power spectrum and main frequency in the FFT analysis of the friction signal.

• Tribology and Lubricants
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• 제19권3호
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• pp.123-132
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• 2003

The effect of surface texture on elastohydrodynamic lubrication (EHL) point contact of a ball Joint mechanism in small reciprocating compressors is studied numerically by using multigrid method. Pressure and film thickness profiles have been calculated for surface roughness with waviness of different orientations and transverse ridge and dent at minimum and maximum Hoes M parameter conditions. The influence of the amplitude and the wavelength of the surface roughness was also studied. Results show that the oblique waviness with orientation angle of 30$^{\circ}$generates the smallest minimum film thickness as compared with those of longitudinal, transverse, and other oblique roughness. The influence of transverse waviness on the minimum film thickness is smaller than for the longitudinal waviness case.

• Bulletin of the Korean Chemical Society
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• 제35권3호
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• pp.731-736
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• 2014

An organic junction transistor with a vertical structure based on an active layer of poly(3-hexylthiophene) was fabricated by facile micro-contact printing combined with the Langmuir-Schaefer technique, without conventional e-beam or photo-lithography. Direct printing and subsequent annealing of Au-nanoparticles provided control over the thickness of the Au electrode and hence control of the electrical contact between the Au electrode and the active layer, ohmic or Schottky. The junction showed similar current-voltage characteristics to an NPN-type transistor. Current through the emitter was simply controllable by the base voltage and a high transconductance of ~0.2 mS was obtained. This novel fabrication method can be applied to amplifying or fast switching organic devices.

• 한국정밀공학회지
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• 제30권4호
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• pp.414-420
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• 2013

We developed inkjet based measurement system for micro-droplet behavior on a substrate. By using the inkjet dispenser, a droplet, which is as small as few pico-liter in volume, can be jetted and the amount can be controlled. After jetting, the droplet image on the substrate is acquired from side view camera. Then, droplet profile is extracted to measure droplet volume, contact angle and evaporation characteristics. Also top view image of the droplet is acquired for better understanding of droplet shape. The previous contact angle measurement method has limitations since it mainly measures the ratio of height and contact diameter of droplet on a substrate. Unlike previous measurement system, our proposed method has advantages because various behavior of droplet on substrate can be effectively analyzed by extracting the droplet profile.

• 한국안광학회지
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• 제19권1호
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• pp.59-67
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• 2014

목적: 콘택트렌즈 관리용품의 살균력 효능 검사법 기준 개발을 위하여 막여과법(Membrane filtration method)과 희석중화법(Dilution-neutralization method)의 살균력 검사 결과를 비교하고 시판되고 있는 콘택트렌즈 관리용품의 살균력을 제시하고자 하였다. 방법: 포도상구균(Staphylococcus aureus), 녹농균(Pseudomonas aeruginosa), 세라티아균(Serratia marces cens), 칸디다균(Candida albicans)을 대상으로 하여 FDA(Food and Drug Administration)기준인 막여과법과 식품의약품안전처에서 새롭게 가이드라인으로 제시할 희석중화법의 살균력 효능 결과를 비교하였으며 총 20종 다목적 용액의 살균력을 측정하였다. 결과: 살균효과가 강한 살균 성분 및 관리용품의 효능은 막여과법과 희석중화법 모두 동일한 결과를 나타냈다. 살균효과가 약한 관리용품의 경우는 막여과법 검사시에는 균이 뭉쳐있어 정확한 균 수 측정이 불가능하였으나 희석중화법 검사시는 정확한 균 수 측정이 가능해짐을 확인하였다. 또한 시판되고 있는 관리용품 중에는 살균력 기준을 통과하지 못한 제품이 존재하였으며 특히 세라티아균과 칸디다균에 대한 살균력이 약한 경우가 많았다. 결론: 막여과법에 비해 희석중화법이 소량의 샘플로 더 정확하게 균수를 측정하는 것이 가능하며 결과 확인이 빨라 살균력 효능 검사시 유용하게 사용될 수 있음을 알 수 있었다.

• 한국정밀공학회지
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• 제29권8호
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• pp.920-926
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• 2012

Wrinkling is a common phenomenon in nature and the shape of a wrinkle can be defined using characteristic dimensions such as pitch, length, amplitude, and density etc. Wrinkle structure can be utilized in various research fields, and especially it has special characteristics when it used in applications of heat transfer; a wrinkly surface has the effect to promote turbulent flow and increasing surface area. However, the generation of wrinkle structures in somewhat regular is not easy. Till now, there are some research works focused on realization of wrinkles in micro scale. However, most of the processes generally requires high precision equipments and high costs, and also there is a limitation to generate the wrinkles in a large area. In this study, we propose a novel method named as a RCO (repetitive contact-and-open) process to fabricate wrinkle structure with low cost and relative easy way. Using the RCO, we fabricated micro-corrugate structures successfully. From the experimental results, we found out the process parameters of RCO, and showed the possibility of RCO to be used in real applications.

• 대한기계학회논문집B
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• 제33권10호
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• pp.789-796
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• 2009

Microdroplet deposition in a micro-groove is studied numerically. The droplet shape is determined by a level-set method which is improved by incorporating a sharp-interface modeling technique for accurately enforcing the matching conditions at the liquid-gas interface and the no-slip and contact angle conditions at an immersed solid surface. The computations are carried out to investigate the droplet behavior derived by the interfacial characteristics between the liquid-gas-solid phases. The effects of contact angle, impact velocity and groove geometry on droplet deposition in a micro-groove are quantified.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.259-264
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• 2004

The hot embossing process as a method for the fabrication of polymer is becoming increasingly important because of its simple process, low cost, high replication fidelity and relatively high throughput. In this paper, we carried out experimental studies and numerical simulations in order to understand the viscous flow of polymer film during hot embossing process. As the initial step of quantitating the hot embossing process, simple parametric studies for the embossing conditions have been carried out using high resolution masters which patterned by DRIE process. Under different embossing times and pressures, the viscous flow of PMMA films into micro/nano cavities has been investigated. Also, the viscous flow during the hot embossing process has been simulated by the continuum based FDM analysis considering micro/nano effect, such as surface tension and contact angle.