Eung Ju Oh

Electrochemical synthesis and characterization of strechable polypyrrole films

Abstract Stretchable polypyrrole (Ppy) films with mixed dopants [di(2-ethyl hexyl)sulfosuccinate with malonic acid(MA), 4-sulfophtalic acid (SPA), dodecylbenzenesulfonic acid (DBSA) etc.] were electrochemically prepared at 0 °C and room temperature and their physical properties were examined. As the temperature employed in synthesis was lowered, the resulting films became more stretchable up to the draw ratio, L/Lo = 2.5 and showed improved thermal stability and electrical conductivity (σ : 255 S/cm). On the other hand, the films prepared at room temperature were elongated up to 1.5 times (σ : 45 S/cm). These phenomena were explained in terms of the molecular weight, structural change due to the temperature and mixed dopants used.

Synthesis and characteristics of soluble polypyrroles with mixed dopants

Abstract Soluble conducting polypyrroles(Ppy) were prepared by the oxidative polymerization of pyrrole using mixed dopants. Compared to the dodecylbenzenesulfonic acid doped polypyrrole [Ppy-DBSA (σRT ∼ 10−1 S/cm)], the Ppy with mixed dopants (Ppy-mixed dopants) showed higher absorption intensity in near IR region in UV-Vis./NIR solution spectra and partly crystalline X-ray diffraction (XRD) patterns and higher conductivity of ∼20 S/cm for free standing films. The Ppy-DBSA film showed three dimensional variable range hopping (3D-VRH) conducton while Ppy-mixed dopant systems 1D-VRH conduction. These results are explained by the packing effect of planar dopant between the polymer chains.

Synthesis of carbazole-containing PPV and its application to the electroluminescent devices

Abstract Carbazole-containing PPV (CC-PPV) was chemically synthesized and demonstrated to be electroluminescent for application to a light emitting diode (LED). Soluble CC-PPV copolymer was prepared from dialdehyde monomer and diphosphonium salt in a mixed solvent (ethanol/chloroform) by the well-known Wittig reaction. The UV–Vis absorption spectrum of CC-PPV copolymer in chloroform has a maximum absorption wavelength at 408 nm, which is caused by the π–π* transition of the conjugated system. In PL spectrum, maximum wavelength of emission was found at 512 nm. From the thermogravimetric analysis (TGA) it was confirmed that the synthesized CC-PPV has a thermal stability up to 180°C. For the fabrication of a LED, the synthesized CC-PPV was dissolved in toluene to prepare an 1.0 wt% solution and the film cast from this solution was demonstrated to be light-emitting at an applied voltage of 3.7 V.

Synthesis and Characterization of Soluble Polyaniline and Its Derivatives Doped with Dialkylsulfates

Abstract Soluble polyaniline and its derivatives doped with dialkylsulfate (DAS : dimethylsulfate, diethyl sulfate, dipropylsulfate etc.) were chemically synthesized. Solubilities of polyaniline doped with DAS (PANI·DAS) powders in polar solvents and polyethoxy aniline doped with DAS (PEtOANI·DAS) powders in various alcohols were observed in the range of 3–8 wt.% and 2–5 wt.%, respectively. This improved solubility in organic polar solvents was explained with the interactions between the hydrophilic sulfonate group, polar substituent and polar solvents. Compared to that of HCl doped polyaniline, PANI·DAS showed improved thermal stability upon heat treatment at 160 °C. The electrical conductivities of PANI·DAS and PEtOANI·DAS films appeared in the range of 1.2∼2.3 S/cm and 10−2∼10−4 S/cm, respectively.

Processing Effects of the Polyvinyl-Butyrol-Based Binder on the Performance of Electroluminescent Diodes

Abstract The processing effects of polyvinyl-butyrol (PVB)-based binding organics (PBBO) on the characteristics of the ZnS:Cu electroluminescent (EL) devices are discussed. The characteristics of the EL devices fabricated using the PBBO are compared with those of devices fabricated using a membrane switch composition (MSC). It is demonstrated that the performance of the PBBO be comparable with the MSC. The brightness and the output current of devices using PBBO at 100 V and 400 Hz are 55 cd/m2 and 2.2 mA, respectively. The reliability test performed under the harsh environment (333 K and 90 % RH) exhibits the life time (time at the half of the original brightness) of device longer than 140 hr.