• 한국군사과학기술학회지
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• 제11권5호
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• pp.71-83
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• 2008

For the major scientific laboratories around the world, nanotechnology has been one of the key scientific issues since the end of the last millenium. The basic materials of this newly emerging technology are nanoparticles, which, in fact, have been used for many centuries. However, the physical properties of the particles were understood quite recently. In order to apply the new properties we have to protect and functionalize the surfaces of the particles, since without protection of the surfaces, nanoparticles grow themselves due to Ostwald Ripening. In this review, the author describes recent technical progress in the field of fuctionalization of various nanoparticles and their applications, so that readers can grasp the overall picture of this new technological field.

• Carbon letters
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• 제14권4호
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• pp.228-233
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• 2013

In this work, we report in-situ observations of changes in catalyst morphology, and of growth termination of individual carbon nanotubes (CNTs), by complete loss of the catalyst particle attached to it. The observations strongly support the growth-termination mechanism of CNT forests or carpets by dynamic morphological evolution of catalyst particles induced by Ostwald ripening, and sub-surface diffusion. We show that in the tip-growth mode, as well as in the base-growth mode, the growth termination of CNT by dissolution of catalyst particles is plausible. This may allow the growth termination mechanism by evolution of catalyst morphology to be applicable to not only CNT forest growth, but also to other growth methods (for example, floating-catalyst chemical vapor deposition), which do not use any supporting layer or substrate beneath a catalyst layer.

• 한국주조공학회지
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• 제23권3호
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• pp.130-136
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• 2003

Rheocasting of AZ91D magnesium alloys yielded the microstructure consisted of the spherical primary particles in the matrix which is different from conventional casting. Rheocast ingots were produced under various processing conditions using batch type rheocaster. Morphology of primary particles was changed from rosette-shape to spherical shape with increasing stirring rate$(V_s)$ and decreasing isothermal stirring temperature$(T_s)$. With increasing $V_s$, more effective shearing between the particles occurred rather than the agglomeration and clustering, so the primary particle size decreased. But with decreasing $T_s$, primary particle size increased mainly due to sintering and partially Ostwald ripening. The sphericity of primary particles increased with increasing $V_s$ and decreasing $T_s$ due to enhanced abrasion among the primary particles. The uniformity of primary particle size increased with increasing Vs and $T_s$.

• 열처리공학회지
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• 제10권2호
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• pp.121-127
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• 1997

In order to elucidate thermal stability of Fe-$Fe_2Ti$ eutectic structure, the initial several structures have been investigated in the changes of coarsening and spheroidization during prolonged annealing under the eutectic temperature. The results are as follows: 1) The rate constant of coarsening and spheroidization was formulated as $S^{-n}-S_0^{-n}=k{\cdot}t$, where S is the total area of the interface between ${\alpha}$ and C($Fe_2Ti$) per unit volume, $S_0$ is initial value and k is the rate constant. 2) The coarsening and spheroidization mechanism was described by Ostwald ripening and controlled by diffusion of Ti-atom in ${\alpha}$-phase. 3) The spheroidization rate constant in eutectic lamellar structures was depended upon annealing temperature and showed the Arrhenius relation. The activation energy for spheroidization of lamellar structure was 365 kJ/mole.

• 한국막학회:학술대회논문집
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• 한국막학회 1995년도 춘계 총회 및 학술발표회
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• pp.1-4
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• 1995

The microstructure of polymer membranes produced via thermally induced phase separation (TIPS) of polymer solutions is a strong function of both the early-stage (by spinodal decomposition or nucleation & growth) and the late-stage phase separation (referred to in general as coarsening). In the case of early stage effects, the membrane morphology resulting from a nucleation & growth mechanism is either a poorly interconnecsed, stringy, beady structure which is mechanically fragile or a well interconnected structure with highly nonuniform pore sizes. In contrast, spinodal decomposition results in a well interconnected, mechanically strong membrane with highly uniform pore sizes. Here I describe recent quantitative studies of the coarsening effects on the microstructure of membranes produced via TIPS process. The dependence of microstructure on coarsening time, quench depth, solution viscosity, and polymer molecular weight was investigated in order to distinguish among three possible coarsening mechanisms, Ostwald ripening, coalescence, and hydrodynamic flow, which may be responsible for structural evolution after the early-stage phase Separation (spinodal decomposition or nucleation & growth).

• 통합자연과학논문집
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• 제14권1호
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• pp.6-10
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• 2021

New materials are very useful due to their wide range of applications, however, they also have caused new pollutants that damage our environment. Chemists have been conscious of the severity of these environmental problems and a great deal of effort has been put into developing environmentally benign chemical processes to synthesize new materials (green synthesis). We also have reported a green synthesis method of synthesizing silver nanoparticles using water-glycerol solution in a previous study. While conducting further research, we have recently discovered that the size of silver nanoparticles is proportional to the quantity of water present in glycerol. This method is completely benign and ecofriendly pathway, as the size of silver nanoparticles is adjusted solely by controlling the quantity of water added to glycerol, without extra additives and energy.

• 대한화장품학회지
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• 제35권3호
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• pp.179-191
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• 2009

본 연구에서는 poly(oxyethylene) hydrogenated castor oils (HCOs)/오일/에탄올/물로 이루어진 에멀젼에 대한 에탄올의 영향을 연구하였다. 에멀젼은 고에너지법인 균질기(homogenizer)를 병합하여 제조하였다. 에멀젼에 대한 에탄올의 영향을 평가하기 위해 입자 크기와 입자 분포 등의 물리적 특성을 측정하였으며 다른 성분의 조성은 같도록 하였다. HCO-20의 경우 에멀젼의 크기가 마이크로미터 크기에서 에탄올이 증가할수록 입자의 크기가 감소하는 것을 확인하였다. HCO-30의 경우 계면활성제 농도 4.00 %에서 입자 크기가 나노미터 크기로 나타났으며, 에탄올의 농도가 4.25 % 일 때 조성 1에서 입자 크기가 $128.15{\pm}1.06nm$이고 조성 2에서는 $136.10{\pm}0.99nm$로 가장 안정한 나노에멀젼이 생성되었다. 마찬가지로 HCO-40은 계면활성제 농도 4.00 %에서 입자가 나노미터 크기로 나타났으며, 에탄올이 4.50%일 때 조성 1에서 입자 크기가 $115.85{\pm}0.78nm$이고 조성 2는 $121.15{\pm}0.35nm$로 안정한 나노에멀젼이 생성되었다. HCO-60의 경우에서는 계면활성제 농도 4.00 %, 에탄올 농도 2.25 %에서 에멀젼의 크기가 $262.35{\pm}0.64nm$인 안정한 나노에멀젼이 생성되었다. 마이크로 크기의 에멀젼에서는 에탄올의 함량이 증가할수록 입자의 크기가 감소하는 것을 알 수 있었고, 나노에멀젼에서는 에탄올의 특정 농도에서 최저값을 나타냄을 확인하였다. 나노에멀젼의 불안정화 과정은 Ostwald ripening에 의한 것으로 보여진다. 계면활성제 종류에 따른 에멀젼에 대한 에탄올의 영향을 연구함으로써 안정한 에멀젼을 만들기 위한 에탄올의 함량을 계산할 수 있을 것으로 사료된다.

• 공업화학
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• 제23권5호
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• pp.467-473
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• 2012

본 연구에서는 레시틴, 에탄올, 오일, Arlacel 60 (sorbitan monostearate) 등을 주성분으로 하고, 최근 화장품과 식품의 원료로서 각광을 받고 있는 피부의 노화방지용 항산화물질인 코엔자임 Q10 (CoQ10)를 기능성 원료로 함유하는 나노 에멀젼을 제조하고자 하였다. 에멀젼 제조방법으로는 반전유화법(phase inversion emulsion method)과 초음파를 이용한 기계적 방법을 사용하였으며, 이 때 에탄올과 레시틴의 영향과 시간의 경과에 따른 안정성과 그 밖의 각종 변수들이 미치는 영향을 알아보고자 하였다. 이를 위하여 입자의 크기, 제타전위, 에멀젼의 형태와 같은 물리적 특성들을 측정해 보았다. 최소크기의 나노에멀젼을 형성하기 위한 CoQ10의 최적 배합농도는 0.8% 정도였고, 계면활성제로서 Arlacel 60 농도에 따른 입자크기의 영향을 보면 3% 정도에서 100 nm 크기의 에멀젼 입자들을 얻을 수 있었다. 본 연구에서의 사용한 최적의 계면활성제 농도범위(2% 이상)에서는 7일 정도가 지난 시점까지 Ostwald ripening 에 따른 입자의 크기 변화가 없었다. 장시간의 경과에 따른 실험을 보면 에멀젼들은 실온에서 270일이 지난 상태에서도 115 nm로 10% 정도만의 크기 변화를 보여 비교적 안정된 상태로 에멀젼을 유지함을 알 수 있었으며, 제타전위 측정으로 시간의 경과에 따른 입자크기의 변화는 응집(flocculation)에 기인한 것으로 판단된다.

• Bulletin of the Korean Chemical Society
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• 제31권9호
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• pp.2547-2552
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• 2010

CdS nano-particulate films were prepared at the air/water interface under Langmuir monolayers of arachidic acid (AA) via interfacial reaction between $Cd^{2+}$ ions in the subphase and $H_2S$ molecules in the gaseous phase. The films were made up of fine CdS nanoparticles with hexagonal Wurtzite crystal structure after reaction. It was revealed that the formation of CdS nano-particulate films depends largely on the experimental conditions. When the films were ripened at room temperature or an increased temperature ($60^{\circ}C$) for one day, numerous holes were appeared due to the dissolution of smaller nanoparticles and the growth of bigger nanoparticles with an improved crystallinity. When the films were ripened further, CdS rodlike nanoparticles with cubic zinc blende crystal structure appeared due to the re-nucleation and growth of CdS nanoparticles at the stacking faults and defect structures of the hexagonal CdS grains. These structures were characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and X-ray diffraction (XRD). These results declare that CdS semiconductor nanoparticles formed at the air/water interface change their morphologies and crystal structures during the ripening process due to dissolution and recrystallization of the particles.

• KSBB Journal
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• 제29권5호
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• pp.385-391
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• 2014

In this study, the emulsion dispersion stability of optimizing storage temperature was investigated. The system was based on oil/water (O/W) emulsions. In order to evaluate the stability, mean diameter of droplet was measured as a function of temperature with various mixed hydrophilic lipophilic balance (HLB). In addition, the correlations between phase inversion temperature (PIT) and the optimum storage temperature were probed. In this system, majority of the smallest droplet was shown at temperature of $20^{\circ}C$ below PIT. Whether the temperature was increased or decreased from the optimum, size of the droplet increased. According to the mixed HLB, the particle size and optimum storage temperature were also affected. As the concentrations of surfactant were increased, the size of particle decreased with lower optimum temperature for storage. If the surfactant (4 wt%) were mixed with HLB, the optimum storage temperature was $21^{\circ}C$ for maintaining the size of smallest droplet at 108.3 nm in diameter. At above optimum condition, increased size of particle was observed approximately 4 % increases from 108.2 nm to 112.3 nm after 600 hours. The size of particle in emulsion was maintained stably without any considerable effect of Ostwald ripening phenomena at the optimum storage temperature with low polydispersity index.