No 3, Vol. 5, 2003 


M. Böhning, H. Goering, N. Hao, R. Mach, F. Oleszak and A. Schönhals

Bundesanstalt für Materialforschung und -prüfung (BAM),
Unter den Eichen 87, D-12205 Berlin, Germany


Plasma synthesized SiC nanoparticles are dispersed in dichloromethane/poly(bisphenol-A-carbonate) (PC) solutions by high power ultrasonification. The nanoparticle dispersion is stabilized during film casting under well adapted preparation conditions. The influence of the SiC nanoparticles on the molecular mobility of the PC is studied by dielectric relaxation spectroscopy using films of about 50 µm thickness. No effect on the cooperative segmental mobility (glass transition) is detected. But the relaxation region corresponding to localised fluctuations is strongly broadened and the activation energy is reduced with increasing nanoparticle concentration. The most significant change is observed in the relaxation region between α- and β-process. Corresponding gas transport properties of these nanocomposite films are characterized in terms of permeability, diffusivity and solubility. Results can be interpreted based on an altered local free volume distribution and a change of molecular mobility of the polymer matrix near the nanoparticle surface. Concentration dependent CO2 permeation experiments reveal a significant reduction of plasticisation effects in the nanocomposites compared to the pure PC film.

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