• Journal of Environmental Science International
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• v.19 no.9
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• pp.1161-1167
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• 2010

The effects of addition of non degradable polymers, polystyrene (PS) and poly(methyl methacrylate) (PMMA) on the rate of enzymatic degradation of biodegradable poly(l-lactide) (PLLA) have been studied in term of surface structure. Since a component in multicomponent polymeric system has shown surface enrichment, PS and PMMA which have lower surface energy than PLLA were selected as a minor blend component (5 wt%). Enzymatic degradation was carried out at $37^{\circ}C$ and pH 8.5 in the aqueous solution of Proteinase K. Two blend systems, partially miscible (PS/PLLA) and immiscible (PMMA/PLLA), showed the surface enrichment of 4 and 2 times of PS and PMMA, respectively. From the weight loss profile data, the slow degradation rate of both blend films was observed. This indicates that PS or PMMA domains which exist at surface act as a retardant of enzymatic attack.

• Biotechnology and Bioprocess Engineering:BBE
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• v.3 no.2
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• pp.103-108
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• 1998

A hydrophobic substrate triolein was hydrolyzed by lipase in a mono-phase reaction system containing cyclodextrin(CD) as emulsifier. The triolein was transformation to an emulsion-like state in the CD containing reaction system in contrast to the oil-droplet like state without CD due to the formation of an inclusion complex between the lipids and CDs. The hydyrolysis reaction increased substantially in the CD containing reaction system, and the optimum reaction conditions including the amount of lipase, ${\beta}$-CD concentration, and mixing ratio of triolein and ${\beta}$-CD, were determined. The performance of the enzyme reaction in a mono-phase reaction system was compared with that of a two-phase reaction system which used water immiscible hexane as the organic solvent. The role of a CD in the mono-phase reaction system was elucidated by comparing the degree of the inclusion complex formation with triolein and oleic acid, Km and Vmax values, and product inhibition by oleic aicd in aqueous and CD containing reaction systems. The resulting enhanced reaction seems to be caused by two phenomena; the increased accessibility of lipase to triolein and reduced product inhibition by oleic acid through the formation of an inclusion complex.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.18 no.2
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• pp.65-69
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• 2013

In situ measurement of a primary production in East Sea, a marginal sea with a fair accessibility, is nonetheless an arduous task because of dynamic variability. In this study, we estimated the mean value of background (gross) primary production over the warm region of the East Sea based on a biogeochemical hypothesis. We propose an immiscible-shoaling hypothesis for the estimation of primary production, which assumes that primary production in the warm region occurred only by the nutrient supply through the Korea Strait. Annual primary production thus estimated is $209\;gC\;m^{-2}\;y^{-1}$, which is comparable to the satellite-based estimates of net primary production in the region. However, since this hypothesis assumes that primary production is based on only the new nutrients supplied to the system, primary production would increase by 40% if we release the assumption, and assume f = 0.6. This suggests that nutrient influx through the Korea Strait alone is more than enough to support primary production previously reported. Primary production may increase as much as two times if we considered other external perturbations excluded intentionally to estimate the background level of primary production, such as coastal upwelling, submerged ground water discharge, aeolian input, ocean dumping, and mixing by typhoons as well as the contribution of cyanobacteria that has not been quantified in the region. This implies the primary production in the warm region of the East Sea would be comparable to that of the Peru upwelling region with f = 0.6.

• Korea-Australia Rheology Journal
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• v.16 no.3
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• pp.135-140
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• 2004

Morphological and rheological properties of the poly(methyl methacrylate) (PMMA) and polystyrene (PS) blends were studied by scanning electron microscopy (SEM) and advanced rheometric expansion system (ARES). From the SEM results, the PMMA-PS blends showed dispersed morphology and the particle size of the dispersed phase was quite small (0.1~0.6 $\mu\textrm{m}$ compared with other immiscible polymer blends. Values of the interfacial tension of the PMMA-PS blend were obtained from the Choi-Schowalter and the Palierne emulsion models using the storage modulus of the PMMA and PS, and found to be 1.0 and 2.0 mN/m, respectively. The interfacial tension between the PMMA and PS was also calculated from the Flory-Huggins polymer-polymer interaction parameter ($\chi$) and found to be from 0.98 to 1.86 mN/m depending on the molecular weight and composition. Comparing the values of the interfacial tension from the Flory-Huggins polymer-polymer interaction parameter and the values measured by oscillatory rheometer, it is suggested that the interfacial tension of the PMMA-PS blend obtained from the polymer-polymer interaction parameter are in good agreement with the values obtained by rheological measurements.

• Journal of Powder Materials
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• v.10 no.1
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• pp.46-50
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• 2003

Lee et al. reported that a mixture of Cu and Ta, the combination of which is characterized by a positive heat of mixing, $\{Delta}H_{mix}$ of +2 kJ/㏖, can be amorphized by mechanical alloying(MA). It is our aim to investigate to what extent the MA is capable of producing a non-equilibrium phase with increasing the heat of mixing. The system chosen is the binary $Cu_{30}Mo_{70}$ with $\{Delta}H_{mix}$=+19 kJ/㏖. The mechanical alloying was carried out using a Fritsch P-5 planetary mill under Ar gas atmosphere. The vial and balls are made of Cu containing 1.8-2.0 wt.%Be to avoid contaminations arising mainly from Fe when steel balls and vial are used. The MA powders were characterized by the X-ray diffraction, EXAFS and thermal analysis. We conclude that two phase mixture of nanocrystalline fcc-Cu and bcc-Mo with grain size of 10 nm is formed by the ball-milling for a 3:7 mixture of pure Cu and Mo, the evidence for which has been deduced from the thermodynamic and structural analysis based on the DSC, X-ray diffraction and EXAFS spectra.

• Coupled systems mechanics
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• v.7 no.1
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• pp.95-109
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• 2018

The relevance of turbulent mixing in estuarine numerical models for stratified two-layer shallow water flows is analysed in this paper. A one-dimensional numerical model was developed for this purpose by extending an immiscible two-layer model with an additional source term, which accounts for turbulent mixing effects, namely the entrainment of fluid from the lower to the upper layer. The entrainment rate is quantified by an empirical equation as a function of the bulk Richardson number. A finite volume method based on an approximated Roe solver was used to solve the governing coupled system of partial differential equations. A comparison of numerical results with and without entrainment is presented to illustrate the influence of entrainment on both the salt-water intrusion length and lower layer dynamics. Furthermore, one example is given to demonstrate how entrainment terms may help to stabilize the numerical scheme and prevent a possible loss of hyperbolicity. Finally, the model with entrainment is validated by comparing the numerical results to field measurements.

• Macromolecular Research
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• v.13 no.3
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• pp.243-252
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• 2005

The effect of the vinyl acetate (VA) content on the thermal, viscoelastic, rheological, morphological and mechanical behaviors in various blends of ethylene-vinyl acetate (EVA)/ethylene-$\alpha$-olefin copolymers was investigated using 28, 22 and $15 mol\%$ of VA in EVA. In the DSC melting and crystallization thermograms of all of the EVA systems blended with ethylene-$\alpha$-olefin copolymers, discrete peaks were observed which were related to the constituents. In the dynamic mechanical thermal analysis, the storage modulus increased with increasing content of ethylene-$\alpha$-olefin copolymers. In addition, the transition regions relating to the tan bpeaks varied with the VA content. The crossover point between G' and G" varied depending on the VA contents, and shear-thinning was more prominent in the EVA/EtBC system. In the SEM investigation, a discrete phase morphology was observed in both the EVA/EtBC and EVA/EtOC blends, but the contrast improved with decreasing VA content. However, the tensile strength and modulus improved, but the elongation at break reduced with decreasing VA content, implying that the ethylene-$\alpha$-olefin copolymers play the role of reinforcing materials. Thus, the EVA and ethylene-$\alpha$-olefin components in the copolymers are immiscible in the molten and solid states, but are nevertheless mechanically compatible.

• Korean Chemical Engineering Research
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• v.52 no.1
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• pp.106-112
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• 2014

Here, we demonstrated the optimum design of pillar microstructure for efficient microdroplet merging. The microfluidic device mainly consisted of programmable microvalves and pillar microstructures. Based on the system, aqueous droplets were continuously generated at T-junction using actuating of integrated programmable microvalaves under the immiscible continuous fluid (mineral oil containing 0.5 wt% Span 80). The principle of merging process depended on the competitive correlation of hydraulic pressure of continuous phase and Laplace pressure of the droplet. We found that the design of the micropillars controls above two pressures. Finally, it was demonstrated that the microfluidic system could be able to efficient biochemical reaction. We expect that the microfluidic system is useful analytical or reaction tools in fundamental science, biotechnology, and chemical engineering.

• Korean Journal of Food Science and Technology
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• v.32 no.2
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• pp.454-460
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• 2000

It is difficult to accurately evaluate the effect of lipophilic compounds in aqueous reaction system of enzymes because they are immiscible with water. To screen lipophilic inhibitors of tyrosinase which catalyzes the synthesis of melanin in vivo, an optically clear organic system composed of organic solvent, surfactant, and water, often called reverse micelles(RM), was introduced. Optimal RM to let tyrosinase act normally was composed of isooctane as an organic solvent and dioctyl sulfosuccinate(AOT) of 100 mM as a surfactant. When a molar ratio of water to surfactant was 15, tyrosinase(105.3 units) in RM showed a similar reactivity toward 3,4-dihydroxyphenylalanine(0.18 mM) as in the aqueous assay system. In the presence of cinnamic acid, the product formation of tyrosinase reaction was proportional to the reaction time. This indicates that the inhibitory effect of lipophilic compounds could be analyzed in RM.

• Applied Chemistry for Engineering
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• v.2 no.3
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• pp.209-215
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• 1991

The effect of agitation on the dispersion of organic phase was investigated in an immiscible liquid system (n-hexane/40 wt % p-TSA aqueous solution). Four different types of six-bladed turbine impellers were used : a flat blade type and three screen blade types. The experimental results showed that the extent of dispersion of organic phase at the same agitation speed was decreased in the order of flat blade, 60 mesh, 40 mesh, and 20 mesh screen blades. Otherwise, it was increased with increasing the concentration of TBA as a surfactant agent and with decreasing volume fraction of organic phase. Also, the minimum agitation speed for a complete dispersion was increased in the order of flat blade, 60 mesh, 40 mesh, and 20 mesh screen blades. However, the minimum power consumption did not vary significantly. In this condition, the relationship between Power number and Reynolds number was expressed as $N_p=a\;N_{Re}{^b}$, where the values of constant a and constant b were ranged 2200~4100 and -0.69~-0.63 respectively.