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Georges Hadziioannou

Publications and source records attributed to Georges Hadziioannou.

4 recordsLinked to original sources
PubMed2005

Impact of structure and morphology on charge transport in semiconducting oligomeric thin-film devices.

We investigated various thin-film morphologies of vacuum-deposited highly luminescent 2,5-di-n-octyloxy-1,4-bis[4'-(styryl)styryl]benzene (Ooct-OPV5) in a typical light-emitting-diode device structure. Important modifications in the thin-film morphology and structure were obtained by changing the substrate temperature in the range 23-90 degrees C. Structural analysis by X-ray and electron diffraction provided clear evidence for polymorphism in evaporated thin films of Ooct-OPV5. Concomitantly, the hole mobility in the corresponding devices was determined by transient electroluminescence measurements. We demonstrate that the substrate temperature T(sub) is a key parameter that controls the hole mobility of the devices. Increasing T(sub) between 23 and 84 degrees C results in a progressive increase of the zero-field hole mobility from 10(-6) to 10(-4) cm(2) V(-1) s(-1). The increase in hole mobility is correlated to the average grain size in the thin films. In addition, we give evidence for the existence of a peculiar growth mode in the bulk crystal structure of Ooct-OPV5, whereby the (a,b) and (b,c) planes can grow in a homoepitaxial manner.

Journal Article↗
PubMed2005

Numerical simulation of polymerization in interdigital multilamination micromixers.

Free radical polymerization in microfluidic devices modeled with the help of numerical simulations is discussed. The simulation method used allows the simultaneous solvation of partial differential equations resulting from the hydrodynamics, thermal and mass transfer (convection, diffusion and chemical reaction). Three microfluidic devices are modeled, two interdigital multilamination micromixers respectively with a large and short focusing section, and a simple T-junction followed by a microtube reactor together considered as a bilamination micromixer with a large focusing section. The simulations show that in spite of the heat released by the polymerization reaction, the thermal transfer in such microfluidic devices is high enough to ensure isothermal conditions. Moreover, for low radial Peclet number, microfluidic devices with a large focusing section can achieve better control over the polymerization than a laboratory scale reactor as the polydispersity index obtained is very close to the theoretical limiting value. As the characteristic dimension of the microfluidic device increases, i.e. for high radial Peclet number, the reactive medium cannot be fully homogenized by the diffusion transport before leaving the system resulting in a high polydispersity index and a loss in the control of the polymerization.

Biological Transport↗