전자종이를 위한 유기나노입자와 전자 잉크 입자 특성에 관한 연구

Abstract

본 연구에서는 강한 형광을 가짐으로 섬유나 종이 등에 발광 광택제로 사용되고 광전도 물질 (photoconductive materials)과 전자 발광 장치(electroluminescence devices) 등에 널리 이용되고 있는 pyrazoline 의 1위치에 페닐기, 3 위치에 나프틸기, 5 위치에 p-디메틸페닐, p-에톡시페닐, p-이소프로필페닐, p-알릴옥시페닐기 등 다양한 치환기를 도입하여 photoluminescence (PL)와 electroluminescnece (EL)의 특성을 증가시켜 피라졸린 유도체를 합성한 후 재침전법 (reprecipitation method)로 다양한 크기(50 - 200 nm)의 유기나노입자 (organic nanoparticle)을 제조하여 입자 크기에 따라 Emission color 가 조절될 수 있음을 관찰하였다. 이렇게 얻어진 물에 분산된 피라졸린 유기나노입자와 계면활성제를 수용성 알콜 혼합 용매에 녹여 methyl methacrylate 을 첨가하여 polymerization 시켜 100 nm 정도의 E-Ink 입자를 제조하였다. 이러한 E-Ink 입자는 혼합 용매의 극성, 다양한 계면활성제의 첨가 및 투입양의 조절, 온도, pH 등을 조절하여 E-Ink 입자의 크기 및 크기 분포를 조절하여 높은 해상도를 가지는 전기영동입자 제조의 최적의 조건을 검토하였다. 유기 합성의 경로를 통해 새로운 E-Ink 입자를 만들 수 있으며 그에 따라 유기나노입자의 특성이 바뀌는 무한한 가능성을 지니고 있다. 본 연구에서 pyrazoline 유도체의 유기나노입자를 이용한 전기영동 E-Ink 입자 제조 및 그 물성 연구는 유기 나노 화학의 학문적 발전에도 큰 기여를 할 것이다. 본 연구의 수행 과정에서 유기 합성, 계면 화학, 분광학적 기기 사용법의 습득으로 매우 큰 학문적 성과를 얻게 될 것으로 기대한다.

We prepared various pyrazoline derivatives which possess dimethylamino-, ethoxy-, isopropyl-phenyl ring at the 5-position of pyrazoline. The nanoparticles of pyrazoline derivative ranging from tens to hundreds of nanometers by the reprecipitation method have been successfully prepared and their optical size-dependent properties have been investigated with UV-vis, fluorescence spectroscopy, DLS (Dynamic Light Scattering) and SEM. The size-dependent optical properties of pyrazoline organic nanoparticles have been observed in the order of dimethylamino- >ethoxy- > isopropyl- in electro-donating characters. Nanoparticles of 1-phenyl-3-naphthyl-5-((ethoxy)phenyl)-2-pyrazoline(PNEP) with sizes ranging from tens to hundreds of nanometers were prepared by the reprecipitation method. Their excitonic transitions responsible for absorption and emission, as compared with those of diluted solution, have been investigated as a function of nanoparticle size. We found that pyrazoline nanoparticles possess an ambiguous size dependence on their optical properties. As the nanoparticle size decreased,the absorption peak of pyrazoline nanoparticles was observed to be shifted to the high-energy side due to size effect. 1-phenyl-3-naphthyl-5-((dimethylamino)phenyl)-2-pyrazoline(PNDP) nanoparticles were polymerized with methyl methacrylate and ethylene glycol dimethacrylate using surfactants. We found that pyrazoline nanoparticles possess a special size dependence in their optical properties. As the nanoparticle size decreased, the absorption and emission peak of pyrazoline nanoparticles were observed to shift to the high-energy side due to the aggregate formation and increased intermolecular interaction in the nanoparticles. The electronic ink particles of pyrazoline organic nanoparticles were successfully prepared by dispersion polymerization in aqueous alcohol medium for full color electronic paper, which is expected to substitute for the future display. In order to improve their mobility, the surfactant was added as a charge control additive. On increasing the amount of surfactants, the ink particle size decreased. The size and morphology of electronic ink particles were characterized by scanning electron microscope. The electrophoretic mobility of the resulting electronic inks was -7.5 to -3.6 x 10^(-5) cm²/V·s in the presence of surfactants.