• Tribology and Lubricants
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• v.33 no.6
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• pp.245-250
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• 2017

In this work, we examine pure water and water with nanoparticles to investigate water lubrication characteristics and the effect of nanoparticles as lubricant additives for different substrates. We test carbon-based coatings and metals such as high-speed steel and stainless steel in pure deionized (DI) water and DI water with nanoparticles. We investigate water lubrication characteristics and the effect of nanoparticles based on the friction coefficient and wear rate for different substrates. The investigation reveals that nanoparticles enhance the friction and wear properties of high-speed steel and stainless steel. The friction coefficient and wear rate of both high-speed steel and stainless steel decreases in DI water with nanoparticles compared with the results in pure DI water. The presence of nanoparticles in water show good lubricating effect at the contact area for both high-speed steel and stainless steel. However, for carbon-based coatings, nanoparticles do not improve friction and wear properties. Rather, the friction coefficient and wear rate increases with an increase in the concentration of nanoparticles in case of water lubrication. Because carbon-based coatings already have good tribological properties in a water environment, nanoparticles in water do not contribute toward improving the friction and wear properties of carbon-based coatings.

• Journal of Korean society of Dental Hygiene
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• v.20 no.4
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• pp.535-543
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• 2020

Objectives: The aim of this study was to investigated the surface roughness and change in the amount of adhesion of Streptococcus mutans to the commercial pit and fissure sealant containing cerium oxide nano particles(CNPs). Methods: The CNPs was incorporated into a commercial pit and fissure sealant at 0-4.0 wt%. Disk Specimens (ϕ 10 mm × 2 mm) were prepared by light polymerization the front and back for 40s. Average surface roughness was measured and Streptococcus mutans adhesion was observed under confocal laser scanning microscopy (CLSM) after 24 hour. Data were statistically analyzed by one-way ANOVA and Tukey HSD^a post-hoc test. Results: Difference of the surface roughness(Ra) between groups was not statistically significant in both non CNPs group and CNPs group(p>0.05). In CNPs group, the amount of S. mutans adhesion was significantly different between control group and decreased in order of CNPs 4.0, CNPs 0.5, CNPs 1.0 and CNPs 2.0(p<0.05). Conclusions: Within the limitation of this study, these aspects of oral bacteria performances suggest potential usefulness of the CNPs incorporation, especially CNPs 1% and 2%, in pit and fissure sealant for inducing antibacterial effect.

• Polymer(Korea)
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• v.37 no.5
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• pp.563-570
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• 2013

Poly(vinyl pivalate) (PVPi) was bulk polymerized to make poly(vinyl alcohol) (PVA) microfibrils to apply for polymeric embolization coils replacing metalic coils. Then, syndiotactic PVA (s-PVA) microfibrils having number-average degree of polymerization of 1100 and s-diad content of 60.4% were prepared via saponification of the PVPi with no separate spinning process. To make s-PVA microfibrils with radiopacity, zirconium dioxide ($ZrO_2$) and barium sulfate ($BaSO_4$) were added into s-PVA microfibrils during saponification. The computed tomography (CT) value indicating radiopacity reached up to over 1000 when the amount of $ZrO_2$ and $BaSO_4$ were 12 and 6 wt%, respectively.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.377-382
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• 2010

The Present study uses non-Newtonian simulant gel propellant mixed by Water, Carbopol 941, and NaOH solution in order to analyze the gel propellant flow behavior. Rheological data have been measured and obtained prior to the analysis of flow characteristics where water-gel propellant as well as water-gel propellant with $Al_2O_3$ nano particles are both used. The critical Dean number were examined by numerical simulation of gel propellant in the U-shape duct flow. It is found that though gel-nano propellants have higher apparent viscosity, the critical Dean number did not showed notable difference with respect to the water-gel propellant. It is believe that this is due to the fact that the power law index of both propellants have close value, as was demonstrated by Fellouah et al.[1]

• Tribology and Lubricants
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• v.25 no.6
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• pp.404-408
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• 2009

In this paper, the relationship between the material removal rate and the interfacial mechanical properties at particle-surface contact situation, which can be seen in an abrasive machining process using micro/nano-sized particles, was discussed. Friction and stiffnesses were measured experimentally on an atomic force microscope (AFM) by using colloidal probes which have a silica colloid particle in place of tip to simulate a particle-flat surface contact in an abrasive machining process. From the experimental investigation and theoretical contact analysis, the interfacial contact properties such as lateral stiffness of contact, friction, the material removal rate were presented with respect to some of material surfaces and the relationship between the properties as well.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.07a
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• pp.35-37
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• 2005

100, 200nm 크기의 colloidal silica 각각에 나노 ceria 입자를 수열합성법으로 코팅하였다. Colloidal silica 입자에 ceria를 코팅 시 slurry의 pH조절과 수열처리에 이용하여 silica에 ceria가 코팅됨을 TEM과 zeta-potential을 이용하여 확인하였다. 연마 슬러리의 분산 안정성과 연마효율을 높이기 위하여 슬러리의 pH 는 9로 하였으며, 이때의 zeta-potential 값은 -25 mV이었다. 1 wt%로 제조된 연마슬러리를 이용하여, 4 inch $SiO_2$, $Si_3N_4$ wafer를 압력변화에 따른 연마특성을 관찰 하였다. Ceria coated colloidal silica 100 nm, 200 nm와 commercial한 $CeO_2$입자를 연마압력 6 psi로 oxide film을 연마한 결과 연마율이 각각 2490 ${\AA}/min$, 4200 ${\AA}/min$, 4300 ${\AA}/min$으로 측정되었다. 또한 $SiO_2$, $Si_3N_4$ film의 6 psi압력에서 ceria coated colloidal silica 100 nm, 200 nm와 commercial 한 $CeO_2$입자의 선택비는 3, 3.8, 6.7 이었다. 입자크기가 클수록 연마율이 높으며, Preston equation을 따라 연마 압력과 연마율이 비례하였다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.6
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• pp.239-244
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• 2019

Two hydrogenation surface modifications, namely hydrogen atmosphere heat treatment and hydrogen plasma treatment, were found to lead to improved dispersion of nanodiamond (ND) seed particles and enhanced nucleation density for deposition of smooth ultrananocrystalline diamond (UNCD) film. After hydrogenation, the C-O and O-H surface functionalities on the surface of nanodiamond particles were converted to the C-H surface functionalities, and the Zeta potential was increased. As the degree of dispersion was improved, the size of nanodiamond aggregates decreased significantly and nucleation density increased dramatically. After hydrogen heat treatment at 600℃, average size of ND particles was greatly reduced from 3.5 ㎛ to 34.5 nm and a very high nucleation of ~3.9 × 10¹¹ nuclei/㎠ was obtained for the seeded Si surface.

• Journal of the Korean Ceramic Society
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• v.41 no.3
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• pp.253-258
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• 2004

Non-aggregated nanoscale $\alpha$-Al$_2$O$_3$ powders were prepared successfully by polyacrylamine (PAA) gel method. The method was very simple and polymer network inhibited the aggregate of $\alpha$-Al$_2$O$_3$ powders. In this investigation, nanoparticles of $\alpha$-Al$_2$O$_3$ with a diameter of about 8-15 nm were fabricated by calcining the gel precusors with various concentrations of aluminum sulfate, acrylamide and N,N'-methylene-bis-acrylamide (BIS) in air at 110$0^{\circ}C$ for 2 h. The molar ratio of aluminum sulfate to acrylamide did not have any influence on the size of particles. On the other hand, as the molar ratio of BIS to acrylamide increased, the size of nanoparticles decreased.

• Proceedings of the Korean Society of Dyers and Finishers Conference
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• 2011.03a
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• pp.55-55
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• 2011

실리카 지지체 위에 은 (silver) 나노 입자를 부착시키는 방법으로는 지지체 표면을 먼저 은입자와 친화성이 큰 amino(-NH2), mercapto(-SH), cyan(-CN) 등의 관능기로 표면처리 하는 방법이 일반적으로 사용된다. 구체적으로 설명하면 첫 단계로 지지체인 실리카입자의 표면을 아민으로 표면 처리 한다. 실리카 입자위에 부착된 아민관능기는 입자 생성의 단계에서 은 (silver) 나노 입자가 붙는 접촉점의 역할과 핵 생성 장소로서의 역할을 하게되고, 아민 관능기의 이런 역할로 실리카 입자 표면에 부착된 핵이 생장하여 입자가 됨으로써 최종적으로 은(silver) 나노 입자가 실리카 지지체위에 부착된 형태의 나노복합체가 형성된다. 분자량이 다른 PVP를 사용하여 제조한, NH2와 SH로 계면처리 된 은-실리카 나노복합체제조를 시도하였다. 사용되는 PVP의 분자량이 증가함에 따라 긴 고분자 사슬에 의하여 생성된 입체장애가 증가하게 되어, 은 핵의 성장에 대한 물리적 장벽이 증가하게 된다. 그러므로 고정화된 은 입자의 크기가 감소하게 된다. 이러한 형상은 NH2기 또는 SH기로 계면 처리된 실리카를 이용하여 제조된 은-실리카 나노복합체 입자들에서 모두 관찰되지만, SH기로 계면처리된 실리카를 사용할 경우 고정화된 은 입자의 수가 더욱 많고, 크기 역시 더욱 균일함을 알 수 있다.

• Applied Chemistry for Engineering
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• v.24 no.3
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• pp.260-265
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• 2013

In this study, nano-emulsions containing 0.01, 0.03, 0.05, and 0.10% ethyl acetate fraction of Hippophae rhamnoides (H. rhamnoides) leaf extracts were prepared. The particle size, particle size distribution and skin permeability of the nano-emulsions were evaluated for five weeks. Nano-emulsion was prepared by the sequential use of homogenizer and microfluidizer. Nano-emulsion containing the ethyl acetate fraction exhibited a monodispersed form. Nano-emulsion containing 0.03% ethyl acetate fraction was the most stable for five weeks. The in vitro skin permeation study of nano-emulsion containing 0.03% ethyl acetate fraction was carried out using Franz diffusion cell. The nano-emulsion showed a better skin permeability than that of O/W emulsion. These results indicate that the nano-emulsion containing the ethyl acetate fraction of H. rhamnoides leaf extract showed a remarkable stability and skin permeability than that of O/W emulsion.