The potential use of polymer light-emitting devices is ultimately limited by their low quantum efficiency as well as by their poor stability against oxygen and moisture. To simultaneously solve these drawbacks, light-emitting devices using the polymer/layered silicate nanocomposite with good gas-barrier properties were fabricated by blending poly[2-methoxy-5-(2‘-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH-PPV) with organoclay. The 2-dimensional nanocomposite film shows higher photoluminescence (PL) output and better photostability when compared with the pure MEH-PPV film of the same thickness. Electroluminescence (EL) efficiency is also enhanced. This 2-dimensional lamellar type nanocomposite structure efficiently confines not only both electrons and holes to enhance the recombination rate but also excitons to improve singlet radiative decay. By analyzing transient EL behavior, it was found that the charge carrier mobility of the nanocomposite device was reduced, which suggests that effective charge blocking improves the bipolar recombination rates. Additionally, the isolation of polymer chains within a confined geometry by intercalation prevents excitons from finding low-energy trap sites. Therefore, PL and EL quantum yield is improved.

SYNOPSISDiffusion coefficients of ethylene glycol (EG) have been measured in poly (ethylene terephthalate) (PET) melts by a quartz-spring sorption apparatus. A simple mathematical model was developed to investigate the sorption behavior accompanied by chemical reactions of EG and PET at high temperatures. Diffusion coefficients are deduced from experimental data for an asymptotically thin sample in order to minimize the effects of reactions. The diffusion coefficient of EG is strongly dependent on the vapor pressure of EG and temperature but not on the molecular weight of PET in this experimental range (degree of polymerization 80-120). The diffusion coefficient of EG in PET melt at 265°C is 2.58 X cm2/s at the limit of zero concentration of EG. The activation energy for diffusion is 38.4 kcal/gmol, and the heat of solution for sorption is -44.9 kcal/gmol. The concentrations of the volatile materials resulting from reactions in PET-EG system were analyzed with gas chromatography. In addition, a fit of the current model to experimental data yields frequency factors for the polymerization reaction ( k , ) and the acetaldehyde formation reaction ( k , ) to be 5.84 X 1 0 ' cm3/mol-min and 3.90 X 10" min-', respectively. Keywords: poly (ethylene terphthalate) , diffusion of ethylene glycol in melts of diffusion coefficient of ethylene glycol in PET melts diffusion with chemical reaction of ethyleneglycol in PET melts

We have studied the dielectric and rheological characteristics of semiconductive polymer based ER fluids. Under static electric field, yield stress of suspension was found to be closely related to the dielectric properties that is in accord with the Maxwell-Wagner interfacial polarization. The dielectric constant showed maximum then decreased with increasing bulk conductivity of particle as the yield stress behaviors did. Particle-medium interaction on ER response was also examined by utilizing appropriate surfactant. These experimental results were consistent with the prediction based on the recent model studies. Over wide range of temperature, our ER fluid maintains its activity so that it can broaden the potential applicability as a smart material.