• 한국환경과학회지
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• 제19권9호
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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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• 제3권2호
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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.

• 한국해양학회지:바다
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• 제18권2호
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• pp.65-69
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• 2013

대륙주변해인 동해의 일차생산력은 조사하기 쉬운 듯하지만 해황의 역동적 변동성 때문에 현장 관측으로 파악하기 매우 어렵다. 이 연구에서는 난수역의 평균적인(총)일차생산 배경값을 생지화학적 가설에 기반하여 추정하였다. 계산에 사용된 비혼합-부상 가설은 일단 일차생산이 오로지 대한해협을 통해 수송된 영양염에 의해서만 일어난다고 가정했을 경우로서, 결과($209\;gC\;m^{-2}\;y^{-1}$)는 발표된 위성기반 순일차생산력과 대등한 것으로 나타났다. 그런데 일차생산이 100% 신생산에 의존한다고 가정했었기 때문에 이 구속을 풀어 신생산지표를 0.6이라 가정하면 일차생산력은 40% 가량 높아진다. 결과는 오로지 대한해협을 통해 유입되는 영양염만으로도 기존에 알려진 일차생산을 지지하고도 남음을 말해준다. 그런데 배경값을 구하기 위해 배제시켰던 여러 가지 변동 요인들, 예컨대 용승, 지하수 유입, 대기 유입, 해양 투기, 태풍 등 배경에 더 해지는 교란은 모두 일차생산을 추가로 부양하는 요인이고, 여기에 아직 정량화 되지 못한 초미소남세균의 광합성에 대한 기여까지 고려하게 되면 실제 일차생산력은 배경값의 두 배 이상도 가능할 것으로 추정된다. 이 경우에 일차생산력은 신생산지표가 0.6으로 알려진 페루 용승역과 비등한 규모가 된다.

• Korea-Australia Rheology Journal
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• 제16권3호
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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.

• 한국분말재료학회지
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• 제10권1호
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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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• 제7권1호
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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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• 제13권3호
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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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• 제52권1호
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• pp.106-112
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• 2014

본 연구에서는 미세액적을 효과적으로 합류시키기 위하여 미세기둥 구조들에 따른 영향 및 정체 현상 조절에 관한 연구를 수행하였다. 최적의 미세액적 합류조건을 찾기 위하여 매우 정교하게 조절이 가능한 미세 밸브를 접목하였다. 수용성 미세액적은 연속상으로 0.5 wt% Span 80이 함유된 미네랄 오일을 사용하였다. 합류과정은 미세유체 칩 내부에 위치한 미세기둥의 구조와 배치를 통해 액적 주위의 압력과 액적 내부의 라플라스 압력의 차이를 조정하여 수행된다. 마지막으로 최적의 합류 구조를 지닌 미세유체시스템에서 효소 생화학반응 실험을 수행함으로써 본 장치가 생물학 및 생화학 실험을 수행하는 유용한 도구로서 사용될 수 있음을 입증하였다.

• 한국식품과학회지
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• 제32권2호
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• pp.454-460
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• 2000

지용성 물질은 물에 용해되지 않아 수용액 효소반응계에서의 특정효과를 평가하기가 어렵다. 생체내에서 멜라닌을 합성하는 효소인 tyrosinase의 지용성 저해제를 탐색하고자 유기용매, 계면활성제 및 물로 구성된 광학적으로 투명한 RM을 도입하였다. Tyrosinase의 겉보기 반응이 물에서와 유사한 RM의 형성조건 중 유기용매는 isooctane, 계면활성제는 100 mM의 dioctyl sulfosuccinate(AOT)가 적절하였다. RM에서 물과 AOT의 몰 농도 비율이 15일 때 tyrosinase(103.5 units)는 기질인 3,4-dihydroxy-L-phenylalanine(0.18 mM)에 대하여 수용액에서와 유사한 거동을 나타내었다. 또한 tyrosinase 저해제인 cinnamic acid 존재 하에서도 tyrosinase 촉매 반응의 반응 생성물이 반응 시간에 비례하여 형성됨이 확인되어 지용성 물질도 RM에서는 tyrosinase 저해활성이 가능함을 시사하였다. 따라서 RM은 수용성인 효소와 기질 그리고 지용성인 저해제를 모두 하나의 상(phase)에 용해시킬 수 있어 지용성 물질의 tyrosinase 저해 효과를 분석할 수 있는 중요한 수단으로 활용할 수 있을 것으로 판단되었다.

• 공업화학
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• 제2권3호
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• pp.209-215
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• 1991

n-헥산과 40 wt % p-TSA 수용액으로 이루어진 비혼화성 액상계에서 교반에 의한 유기상의 분산을 해석하였다. 사용된 교반기는 blade의 형태가 flat와 금망으로 된 4가지 형태의 6-bladed turbine 교반기를 사용하였다. 실험결과, 동일한 교반속도에서 유기상의 분산정도는 blade의 형태가 flat, 60 mesh, 40 mesh, 20 mesh의 순서로 감소하였고 계면활성제인 TBA의 농도가 증가할수록, 그리고 유기상의 부피비가 작을수록 유기상은 잘 분산되었다. 또한 완전분산에 필요한 최소교반속도는 flat, 60 mesh, 40 mesh, 20 mesh의 순서로 증가하였으나 최소소요동력은 거의 동일하였다. 이때 Power number와 Reynolds number와의 관계는 $N_p=a\;N_{Re}{^b}$ 이었으며 교반기의 형태에 따른 상수 a와 혼합계의 종류에 따른 상수 b의 값은 각각 2200~4100, -0.69~-0.63 범위이었다.