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Articles : The Sorption and Permeation Of CO2 and CH4 for Dimethylated Polysulfone Membrane
( Hyun Joon Kim ),( Suk In Hong ) 한국화학공학회 1997 Korean Journal of Chemical Engineering Vol.14 No.3
The sorption and permeation properties of the CO₂ and CH₄ were measured for polysulfone and dimethylated polysulfone to investigate the structure-property relationships. The effect of operating pressure on the transport properties of the polysulfones was examined. The permeation properties for a mixture of CO₂and CH₄(CO₂/CH₄=57.5/42.5 vol%) were also measured and these results were compared with those obtained from the experiments of pure gases. The sorptions of CO₂and CH₄are well described by $quot;dual-sorption model$quot;. The permeability coefficients of CO₂and CH₄decreases with increasing upstream pressure, as is often the case with other glassy polymers. The permeability coefficients of each gas of binary mixture are reduced than those for pure gases. This result is due to the competition of each gas for the Langmuir sites. The free volume of the dimethylated polysulfone is lower than that of polysulfone, and dimethylated polysulfone shows relatively lower permeability coefficients and higher selectivity than polysulfone.
Hyun-Joon Kim,Tae-Seok Oh,Dae-Eun Kim IEEE 2009 IEEE transactions on magnetics Vol.45 No.5
<P>Silicon probe tips are used widely in micro and nano-systems such as AFM, MEMS, and probe recording. The mechanical integrity of the tip is important to assure reliable performance of the tip during contact as well as sliding. Crystalline silicon normally forms a tetrahedral structure, however, under high pressure it is known that the structure transforms to a different phase. This can cause a change in the contact phenomena. In this work, the silicon probe tip deformation process during nano-indentation was investigated by using molecular dynamics simulation. In addition, scribing simulation was carried out to observe the frictional characteristics of crystalline and amorphous silicon structures. The simulation results showed that the structure of silicon near the surface was permanently deformed at a contact stress of approximately 17 GN/m<SUP>2</SUP> and the deformation process could be monitored by observing the bond-angle distribution graph. It was also found that the atomic structure of the silicon tip in the contact region affected the frictional behavior of the tip with respect to fluctuation periodicity and magnitude.</P>
Nano-scale Friction : A Review
Hyun-Joon Kim,Dae-Eun Kim 한국정밀공학회 2009 International Journal of Precision Engineering and Vol.10 No.2
Frictionalforce is a resistant force that must be overcome to achieve relative motion between tow components in contact. The economical and technological benefits of controlling friction and wear are tremendous. However, due to the complex nature of the phenomena, clear understanding of the mechanisms are yet to be achieved, particularly at the nano-scale where surface forces tend to dominate the tribological behavior of the syste. In this paper the results of numerous theoretical, experimental, and numerical works on the fundamental mechanisms of friction at the nano-scale are reviewed. It is shown that friction coefficient values for nano-scale systems are quite varied depending on the conditions under which the system is investigated. As for the mechanism that causes friction at the nano-scale, interaction of the atoms plays a vital role. Furthermore, factors such as atomic radius, interatomic potential energy, and lattice parameters contribute to the degree of atomic interaction.
Articles : The Transport Properties of CO2 and CH4 for Trimethylsilylated Polysulfone Membrane
( Hyun Joon Kim ),( Suk In Hong ) 한국화학공학회 1997 Korean Journal of Chemical Engineering Vol.14 No.5
The transport properties of CO₂and CH₄for TMSPSf (bisphenol A trimethylsilylated polysulfone) were measured, and compared with the values for PSf (bisphenol A polysulfone) and MPSf (bisphenol A methylated polysulfone) to explain the effect of molecular structure of polysulfones on gas transport properties. The permeability coefficients of three polysulfones rank in the order: TMSPSf$gt;PSf$gt;MPSf. TMSPSf is several times more permeable than PSf. The effect of the substituents on chain packing was related to the gas transport properties. The ranking of permeability coefficient correlates well with fractional free volume. The variation of d-spacing is also reasonably consistent with the permeability coefficient. The effects of pressure on the sorption and permeation properties of polysulfones were examined. The permeation properties for a mixture of CO₂and CH₄were also measured and these results were compared with the values of pure gases. The sorbed concentrations and permeability coefficients are well fitted to dual mode model. The permeability coefficients of each gas of binary mixture are reduced than those for pure gases, and the extent of reduction in permeability coefficient is the smallest for TMSPSf, which has the highest value of Langmuir capacity constant.