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DLC 코팅에 의한 PVdF-HFP 막의 표면변화 및 접촉각 연구
이태동,조현,윤수종,김태규,Lee, Tae Dong,Cho, Hyun,Yoon, Su Jong,Kim, Tae Gyu 한국결정성장학회 2014 한국결정성장학회지 Vol.24 No.1
전기방사법(Electrospinning technique)을 이용하여 PVdF-HFP(Poly vinylidene fluoride-co-hexafluoropropylene) 멤브레인을 제조하고, 그 멤브레인 표면위에 DLC(Diamond-like carbon) 코팅공정을 적용하여 멤브레인의 표면변화 및 접촉각 변화를 조사하였다. Ar 플라즈마 처리시간 및 처리조건에 따라 PVdF-HFP 멤브레인 파이버 표면이 주름(wrinkles)형태로 변화 하였다. 이러한 Ar 플라즈마 처리가 된 PVdF-HFP 멤브레인은 초친수성(super-hydrophilic) 특성으로 변했지만, 초친수성 PVdF-HFP 멤브레인에 DLC 코팅공정을 적용하면 반대로 초소수성(super-hydrophobic) 특성으로 변화되었다. 이러한 특성을 가진 표면을 접촉각 측정과 XPS, FE-SEM 측정으로 분석하였다. 따라서 화학적 조성과 표면 형상에 의해 접촉각 특성을 가지는 것으로 확인하였다. Poly vinylidene fluoride-co-hexafluoropropylene (PVdF-HFP) membrane were prepared by the electrospinning technique. We had applied a DLC coating process and then the surface of the membrane and the contact angle change was investigated. Electrospun fibrous PVdF-HFP membrane surface became to wrinkled shape by Ar plasma treatment and treatment conditions. The wrinkled surface of PVdF-HFP membrane became super-hydrophilic. However, after DLC coating process, it became super-hydrophobic. The resulting surfaces were characterized by water contact angle measurement, X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FE-SEM). Resultantly it was recognized that the wettability characteristics of the membrane surfaces depended on the chemical composition and surface morphology.
Network Analysis of Free Trade Agreements: Homophily and Transitivity
이태동,배병인 한국국제정치학회 2013 The Korean Journal of International Studies Vol.11 No.2
Accompanying the unprecedented outburst of Free Trade Agreements (FTAs), scholarly interests in the new wave of regionalism have been flourishing. Yet, notwithstanding its contribution, extant literature has paid little attention to an important aspect of FTA formation: the choice of FTA partners and the underlying structure of the FTA network. While theoretical conjectures about likely FTA partners are abundant, systematic empirical analysis is scant. We attempt to fill this gap by utilizing the concept of “transitivity” and “homophily” in social network analysis. The notion of transitivity refers that “a friend of a friend is a friend” among triads of actors, while homophily is the tendency to form social ties to the similarity in actors’ attributes. Of the various nodal attributes, three are singled out as the most important: political institutions, regionalism, and economic attributes. Using the Exponential Family Random Graph (ERG) model, we show that economic attributes produce mixed results in predicting FTA partners, whereas homophily in region explains FTA tie formation. In line with previous works, we also find strong association between democracy and FTA formation. Our empirical models suggest transitivity in FTA networks referring that an FTA partner of an FTA partner is likely to be an FTA partner.