ABSTRACT:Polyimide-silica hybrid materials with covalently bound phases were prepared via a sol-gel process. The starting materials were p-aminophenyltrimethoxysilane terminated poly(amic acid)s of controlled molecular weight ranging from 5000 to 10000 g mo! -1 and tetramethoxysilane. Optical transparency of the final films increases with the number of bonds between phases. The dependence of the thermal and mechanical properties and morphology on the silica content and/or concentration of bonds between phases were studied.

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The whole bed height of a bio®lter was divided into four individual reactor stages in series. This con®guration permits a measurement of the leachate pH of each stage individually and minimizes interstage mixing of the immobilized culture. The extent to which the residence time of pollutant in the ®lter bed in¯uenced biodegradation characteristics and the composition of immobilized culture under conditions of a constant loading rate was studied using a perlite bio®lter having an internal diameter of 50 mm and the bed height of each stage being 27 cm. The residence time of pollutant in the bed had no in¯uence on the removal ef®ciency and the elimination capacity of the whole bio®lter although some changes of these parameters in the individual stages were observed. The bio®lter achieved an elimination capacity of 140 gm À3 h À1 at removal ef®ciencies greater than 90%. Degradation activity decreased the pH value of the leachate to 3.5±3.0. Microbial analyses showed that styrene was degraded by eukaryotic cells at low pH values. At pH values above 4.0 prokaryotes were also present in the mixed culture.

The adsorption state and dispersion effect of an anionic polyelectrolyte (Dolapix CE64) dispersant on the stability of nanocrystalline ZrO2 suspensions are studied by using adsorption isotherms, sedimentation, TGA, electrokinetic sonic amplitude (ESA) and Auger electron spectroscopy (AES) techniques. It was found that colloidal stability and surface properties of aqueous ZrO2 suspension are closely related to coverage distribution of polyelectrolyte as a function of pH on nanocrystalline ZrO2 particle surface. The amount of polyelectrolyte adsorbed on nanocrystalline ZrO2 particle surface increases greatly with decreasing pHiep (pH 3.72) and increasing the polymer concentration. The results obtained from electroacoustic (ESA) technique and AES spectra of polyelectrolyte adsorbed on nanocrystalline ZrO2 surface proved that both techniques are very effective ways to measure the distribution state of polyelectrolyte on nanocrystalline ceramic powder and reveal how the distribution affect the stability of the suspension. It was found that stabilization can be achieved only when conditions of both Dolapix CE64 ionization and ZrO2 surface coverage are satisfied, suggesting an electrosteric stabilization mechanism. In conclusion, we hypothesized a stabilization model according to the model of two particles approaching to describe the influence of the adsorbed anionic polyelectrolyte configuration on particle surface and the stability of nanocrystalline ZrO2 suspensions.