• The Journal of Korean Academy of Prosthodontics
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• v.45 no.2
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• pp.274-282
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• 2007

Statement of problem: Main consideration was given to the stresses at the site of implant entry into the cortical bone at the alveolar crest. As a suspectible factor affecting the occurrence of stress concentrations, the contact angle between the implant and the alveolar crest bone was addressed. Purpose: The purpose of this study is to evaluate angles between the alveolar crest bone and the implant effect on the implant crestal area induced stresses using a finite element method. Material and methods: Cylindrically shaped, standard size ITI implants entering into alveolar crest with four different contact angles of 0, 15, 30, and 45 deg. with the long axis of the implant were axisymmetrically modelled. Alterations of stresses around the implants were computed and compared at the cervical cortical bone. Results and conclusion: The results demonstrated that regardless of the difference of the implant/alveolar crest bone contact angles, stress concentration occurred at the cervical bone and the angle differences led to insignificant variations in stress level.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1098-1102
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• 2008

To increase the ink transfer rate in the micro-gravure-offset printing, the liquid transfer process between two separating plates is investigated. During the liquid transfer process, in which one plate is fixed and the other one moves vertically, a sessile droplet is separated into two droplets. The volume ratio of the two droplets depends on the contact angles of the two plates. In a numerical study of the ink transfer processes, liquid transfer between two parallel separating plates and between a trapezoidal cavity and an upward moving plate are simulated, as models of the printing of ink from the offset pad onto the substrate and the picking up of ink from the gravure plate by the offset pad, respectively. Also, in experimental study, to obtain various surface contact angles, chemical treatment, plasma treatment, and electrowetting- on-dielectric (EWOD) surface are considered. The transfer rate between two plates is calculated by analyzing the droplet images. From the results, the optimal surface contact angles of the units of the micro-gravure-offset printing can be characterized.

• Tribology and Lubricants
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• v.33 no.5
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• pp.202-206
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• 2017

In this study, the hydrophobicity properties for riblet surfaces that replicate shark skin are simulated. Riblet surfaces with surface roughness on riblets are generated numerically based on the measured data of real shark skin. We assumed that a rib on a scale is hemi-elliptical surface. The surface used in the simulation for the calculation of contact angle is composed of 9 scales like checkerboard type with a roughness. The contact angle of a water droplet can be calculated using the Wenzel equation and Cassie-Baxter equation for the generated riblet surfaces. The variation of contact angles with a fractional depth of penetration for the generated shark skin surfaces without and with coatings is demonstrated in the condition of solid-air-water. The results show that the contact angle for the surface without coating decreases with an increase of the fractional depth of penetration more drastically than that for the surface with coating. We compared the experimental and simulated results. It is shown that the measured contact angles of the shark skin template and the shark skin replica are within the simulated results. Therefore the contact angle of water droplet for rough surfaces can be estimated by the developed numerical method in this study.

• Journal of Korean Ophthalmic Optics Society
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• v.16 no.1
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• pp.31-40
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• 2011

Purpose: This study was performed to investigate the actual state about ultrasonic cleaning of soft contact lenses in local optical shops and evaluate the removal effect of protein deposit on soft contact lenses with different lens containers by ultrasonic cleaner for eyeglasses. Methods: The actual state about ultrasonic cleaning of soft contact lenses was surveyed in total 75 local optical shops in Seoul, Korea. The cleaning efficacy of different lens containers was compared by measuring the protein remained on ocufilcon D contact lenses after washing by an ultrasonic cleaner for eyeglasses. The changes on surfaces and wetting angles of ocufilcon D contact lenses by repeat ultrasonication were further investigated. Results: The main purpose to use ultrasonic cleaners in local optical shops was rapid cleaning. The ultrasonic cleaning efficacy of ocufilcon D contact lenses with glass containers was little higher than it with plastic containers, but was not significantly different. The changes on surfaces and wetting angles of ocufilcon D contact lenses in a plastic lens container by repeat ultrasonication such as 30 and/or 60 times were shown. Conclusions: There was not significant difference in cleaning efficacy between glass and plastic lens containers. However, repeat cleaning with ultrasonic cleaner for eyeglasses would be carefully considered since some significant changes in the parameters of lens surface and wetting angles were detected by repeat ultrasonification even when lens containers were used for ocufilcon D contact lens during ultrasonictions.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.6
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• pp.559-566
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• 2013

The effects of solid surface roughness on the contact angle of a nanofluid droplet were experimentally investigated. The experiments were conducted using the solid surface of a 10 mm cubic copper block and the nanofluid of water mixed with CuO nanoparticles. The experimental results showed that the contact angles of nanofluid droplets were lower than those of water droplets and that the contact angle of the nanofluid droplet increased with the solid surface roughness. Furthermore, it was found that the contact angles of water droplets on the solid surface quenched by both water and the nanofluid were lower than those of water droplets on the pure solid surface. However, significant differences were not observed between the contact angles on the solid surfaces quenched by water and the nanofluid.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.5
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• pp.424-429
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• 2008

Surface wettability in terms of the size of the micro nano structures has been examined. To evaluate the influence of the nano structures on the contact angles, we fabricated two different kinds of structures: squarepillar-type microstructure with nano-protrusions and without nano-protrusions. Microstructure and nanostructure arrays were fabricated by deep reactive ion etching (DRIE) and reactive ion etching (RIE) processes, respectively. And plasma polymerized fluorocarbon (PPFC) was finally deposited onto the fabricated structures. Average value of the measured contact angles from microstructures with nanoprotrusions was $6.37^{\circ}$ higher than that from microstructures without nano-protrusions. This result indicates that the nano-protrusions give a crucial effect to increase the contact angle.

• Korean Membrane Journal
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• v.4 no.1
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• pp.20-24
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• 2002

The surface of polysulfone membranes has been modified using the fluorine chemicals, ITFE (2-iodo-1,1,1-trifluoro-ethane F.W.=209.94) and PFPI (1H,1H-pentafluoro-n-propyl iodide F.W.=259.95), and PFI (1H,1H,2H,2H-perfluorohexyl iodide, F.W.=373.99) based on Friedel-Crafts reaction mechanism with varying reaction temperatures, reaction time, and catalysis types. The resulting membranes were characterized through mainly the contact angle measurement and pure water permeability. The smaller reactant shows the larger contact angles. FeBr$_3$ catalyst is more effective than AlCl$_3$. Typically, the PS film treated with ITFE at $25^{\circ}C$ under FeBr$_3$ catalyst showed the contact angle 78.5$^{\circ}C$ which indicated 10% over the value of unreacted PS films. More than 50% of pure water flux 8.0 g/$m^2$hr, reduced at reaction time 10 min relative to the original flux, 3.49 g/$m^2$hr.

• Advances in concrete construction
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• v.11 no.4
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• pp.323-333
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• 2021

The main objective of this study is to characterize and evaluate the hydrophobic performance of polymer-based water-repellent coatings on cementitious mortar surfaces. Different concentrations of poly(vinyl acetate) (PVAc) and poly(1,4-butylene adipate) (PBA) were prepared in the laboratory and their applicability and performance was tested experimentally by water absorption test and analysis of surface contact angles of cementitious mortar specimens. According to the results of this study, it can be stated that incorporation of nano polymer particles on the surface of cementitious mortar specimens can enhance contact angles and reduce water absorption by increasing hydrophobicity. However, a dosage limit exists for polymer materials in coating, and observed hydrophobic improvements decreases when polymer dosage reached beyond the limit. Additionally, it is observed that water absorption of polymer coated cementitious mortars is closely related with the results of surface contact angle.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.2
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• pp.171-178
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• 2014

In this study, the apparent contact angle on the hydrophilic/hydrophobic surfaces with micropillars was studied. The previous researches showed that the Wenzel equation and the Cassie-Baxter equation were thermodynamically derived for the rough hydrophilic/hydrophobic surfaces and generally referenced on the field of wetting phenomena. For the verification of both equations, the apparent contact angle on the hydrophilic/hydrophobic surfaces with micro-pillars was measured. In the comparison between the measured and estimated apparent contact angles with the equations, the differences between the apparent contact angles were analyzed. Conclusively, the available range and limitation of theoretical equations were investigated and further researches about the apparent contact angle on the rough surfaces were proposed.

• Journal of Korean Foot and Ankle Society
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• v.14 no.1
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• pp.5-10
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• 2010

Purpose: This study was performed to compare the contact area between three different correcting angles after the proximal crescentic and Ludloff osteotomies of the first metatarsal. Materials and Methods: We used the two sawbone models. Proximal crescentic (PCO) and Ludloff osteotomies (LO) were performed and secured using K-wires under the correcting intermetatarsal angle (IMA) $5^{\circ}$, $10^{\circ}$, and $15^{\circ}$. Then each 6 osteotomized model was scanned five times and measured the contact area using the calculating program. We excluded the highest and lowest values. Results: The mean area of cutting surface was 189 $mm^2$ in PCO, 863 $mm^2$ in LO. The mean contact area (contact ratio; contact area $\times$100/area of cutting surface) of PCO was 149 $mm^2$ (79%) in $5^{\circ}$, 139.5 $mm^2$ (74%) in $10^{\circ}$, 107 $mm^2$ (57%) in $15^{\circ}$ IMA. The mean contact area (contact ratio) of LO was 711 $mm^2$ (82%) in $5^{\circ}$, 535.5 $mm^2$ (62%) in $10^{\circ}$, 330 $mm^2$ (38%) in $15^{\circ}$ IMA. Conclusion: A significant decrease in the contact area and contact ratio according to increase in correcting IMA was noticed in LO. We recommend the PCO rather than LO, when the IMA is needed to correct over $15^{\circ}$.