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Solution Viscosity of Polar Perfluoropolyether Lubricants
Jhon, Myung S.,Izumisawa, Satoru,Choi, Hyoung Jin 한국공업화학회 2003 Journal of Industrial and Engineering Chemistry Vol.9 No.5
It is commonly known that the roughness and uniformity of the perfluoropolyether (PFPE) thin lubricant films depend on the solvent used. To determine this solvent effect during the dip-coating process, we examined the viscosity for dilute PFPE solutions, which depends on aspect ratio and interacting potential among PFPE molecules. We found that the intrinsic viscosity, or Huggins' coefficient, measured in the early stage of manufacturing steps, is related to the film morphology, or media noise.
SLIDERS FOR THE NEXT GENERATION MAGNETIC HARD DISK DRIVE SYSTEMS - NUMERICAL SIMULATION
Myung S. Jhon,Paul R. Peck,Soo-Choon Kang,Benjamin L. Wang,In-Eung Kim,Ki-Ook Park 한국자기학회 1995 韓國磁氣學會誌 Vol.5 No.5
Fundamental issues and general procedures of modeling the head disk interface (HDI) in order to provide design criteria for future ultra-low flying sliders are given. Intermittent contact and gaseous rarefaction effects are discussed using nonconventional kinetic theory. To illustrate the simulation results, we modeled IBM 3370 taper flat sliders and positive/negative bow tie sliders. Several alternative HDI concepts for future disk drives - viscoelastic bearings, a hybrid system, and contact recording - are also briefly discussed.
Polymer Conformation in an Extensional Flow with Bead - Wall Hydrodynamic Interacti
Jhon, Myung S,Choi, Hyoung J,Armstrong, Robert 한국화학공학회 1988 NICE Vol.6 No.4
A simplified investigation into the properties of polymers near surfaces in a flow field is presented. A kinetic theory for a two-bead harmonic dumbbell model is derived, centering primarily on the effect of anisotropic hydrodynamics due to the presence of a wall. A comparison of the anisotropic and isotropic cases is made, and it is found that the difference manifest in the polymer concentration is only substantial at relatively high strain rates, or within a few molecular diameters of the wall for realistic values of molecular parameters.
Effect of Temperature on Polymer Migration
Jhon, Myung S,Inn, Yong Woo,Choi, Hyoung Jin 한국화학공학회 1990 NICE Vol.8 No.3
In this study, we investigated the temperture gradient effect on the polymic dynamics in a flow field. To simplify our analysis. we adapted a two-bead hatmonic dumbbell model and found that there were significant effects on the polymer migration no only due to the nonhomogeneity of the flow field, but also due to the temperature difference.
전명식(Myung S. Jhon),강수춘(Soo-Choon Kang),김재영(Jai-Young Kim) 한국자기학회 1997 韓國磁氣學會誌 Vol.7 No.2
A personal computer equipped with high recording density capabilities will become critical for individual users in the upcoming multimedia era. The United States and Japan have established their own information storage research consortia, the National Storage Industry Consortium (NSIC-USA) and the Storage Research Consortium (SRC-Japan), in collaboration with governments, industries, and universities to expand their information technologies for the 21st century. In this paper, we present NSIC’s research trends as examples and suggest the necessity of establishing a similar research consortium in Korea.
Molecular Spreading of Pure and Binary Mixture PFPE Nano Films on Carbon-Overcoated Disks
Chung, Pil Seung,Jhon, Myung S. IEEE 2010 IEEE transactions on magnetics Vol.46 No.6
<P> Due to continuous increase in areal density, the head-media spacing combining head & media overcoat, lubricant film and fly height, is expected to be less than 6.5 nm for 1 <TEX>$\hbox {Tbits/in}^{2}$</TEX> hard disk drives (HDDs). The intermittent contacts between head and disk during operation are unavoidable and cause lubricant depletion in the film. Therefore, the nanoscale conformation and self-healing ability (i.e., spreading) of perfluoropolyether (PFPE) lubricant nano films is critically important in the head-disk interface to maintain long-term reliability of HDDs. In this paper, the spreading phenomena for pure and binary mixture PFPE lubricant nano films on the carbon-overcoated media were examined via molecular dynamics simulation. </P>
곡선경계처리법을 이용한 주기적으로 진동하는 실린더주위의 유동해석
김형민(Hyung Min Kim),Myung S. Jhon 대한기계학회 2007 大韓機械學會論文集B Vol.31 No.11
CMBT(Curved Moving Boundary Treatment) is a newly developed scheme for the treatment of a no slip condition on the curved solid wall of moving obstacle in a flow field. In our research, CMBT was used to perform LBM simulation of a flow over a moving circular cylinder to determine the flow feature and aerodynamics characteristic of the cylinder. To ascertain the applicability of CMBT on the complex shape of the obstacle, it was first simulated for the case of the flow over a fixed circular cylinder in a channel and the results were compared against the solution of Navier-Stokes equation with deforming mesh technique. The simulations were performed in a moderate range of reynolds number at each moving cylinder to identify the flow feature and aerodynamic characteristics of circular cylinder in a channel. The drag coefficients of the cylinder were calculated from the simulation results. We have numerically confirmed that the critical reynolds number for vortex shedding is ar Re=250 and the result is the same as the case of fixed cylinder. As the cylinder approaching to one wall, the 2nd vortex is developed by interacting with the wall boundary-layer vorticity. As the velocity ratio increase the third vortex are generated by interacting with the 2nd vortexes developed on the upper and lower wall boundary layer. The resultant Cd decrease as reynolds number increasing and the Cd approached to a value when Re>1000.
Microscopic Spreading of Nonreactive Perfluoropolyalkylether Film on Amorphous Carbon Surfaces
Kim, Min Chan,Jhon, Myung S . 한국화학공학회 2000 Korean Journal of Chemical Engineering Vol.17 No.4
A spreading mechanism of nonfunctional perfluoropolyalkylehter (PFPE) on carbon surfaces is proposed. For the thin thin-film regime, adsorption-desorption is a main driving force for spreading, and the surface diffusion coefficients increase as the film thickness increases. A two-dimensional virial equation is employed to explain the dependency of surface diffusion coefficient on the film thickness. For the thick thin-film regime, the spreading characteristic is determined by the disjoining pressure gradient. We adopt a slip boundary condition to analyze the thick thin-flim regime. This modification of the boundary condition reasonably explains the dependence of surface diffusion coefficients on flim thickness.
Kim, Soo,Kim, Chunjoong,Jhon, Young-In,Noh, Jae-Kyo,Vemuri, Sesha Hari,Smith, Robert,Chung, Kyung Yoon,Jhon, Myung S.,Cho, Byung-Won The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.48
<P>Li<SUB>2</SUB>MnO<SUB>3</SUB>-stabilized LiCoO<SUB>2</SUB> electrode materials were synthesized using the method of mechanochemical process. Li<SUB>2</SUB>MnO<SUB>3</SUB> was prepared and the mechanochemical process was carried out with LiCoO<SUB>2</SUB>, which yielded the layered–layered integrated structure nanocomposites. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy studies confirmed the structural integration of 0.5Li<SUB>2</SUB>MnO<SUB>3</SUB>·0.5LiCoO<SUB>2</SUB> electrode materials. We also performed the high temperature heat treatment, where our 0.5Li<SUB>2</SUB>MnO<SUB>3</SUB>·0.5LiCoO<SUB>2</SUB> electrode materials showed improvement in the discharge capacity (∼180 mA h g<SUP>−1</SUP>) with good cycleability. To obtain a physical insight into the performance of the nanocomposite structure, we carried out first principles calculations to obtain activation energy barriers of Li<SUP>+</SUP> de-/intercalation, which suggested that utilizing both Li<SUB>2</SUB>MnO<SUB>3</SUB> and LiCoO<SUB>2</SUB> components can enhance the Li<SUP>+</SUP> diffusion for the layered–layered integrated structure.</P> <P>Graphic Abstract</P><P>Li<SUB>2</SUB>MnO<SUB>3</SUB>-stabilized LiCoO<SUB>2</SUB> electrode materials were synthesized using the method of mechanochemical process. First principles calculations were carried out to further obtain the physical insight of the layered-layered system. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm35654f'> </P>