Wolfgang Bürger

Determination of the surface tension of microporous membranes using wetting kinetics measurements

Abstract In this paper, a new method is introduced to determine the surface tension of the solid material from which a porous membrane is made. The method is based on the well known determination of the penetration velocity of the liquid that penetrates into a porous structure. A modified Washburn equation is applied to interpret the experimental data. Whereas the use of this equation has been well investigated on powder packages, it has not been used on microporous membranes until now. To test the applicability of the Washburn equation for microporous membranes, samples made from poly(tetrafluoroethylene), poly(ethylene), and poly(propylene), with different porosities, were investigated. All membranes were tested using a series of alkanes with different liquid surface tensions. A plot of the normalized penetration velocity as a function of the liquid surface tension shows a maximum if both liquid and solid surface tensions are equal. It was found that the use of the modified Washburn equation gives relevant solid surface tension values for different types of membranes and offers a way to determine the solid surface tension of the material from which a microporous membrane is made, independent of its pore geometry.

Reaktionen terminaler Perfluoralkene mit Diaminen und Diphenolen

Abstract Model compounds related to the reaction products of perfluoroalkenes produced by theelectron-beam irradiation of poly(tetrafluoroethylene) with dinucleophilic reactants havebeen synthesized. Such model compounds, in reaction with diphenols or diamines, giveinformation relating to the mechanism of crosslinking reactions. Results obtained withperfluorohept-1-ene show that terminal perfluoroalkenes react preferentially with dinucleophilicreactants to give unsaturated ether and amide structures

Potentiometrische Titration von oberflächennahen Carboxygruppen in bestrahlten Fluorpolymeren

Bei der Elektronenbestrahlung von Fluorpolymeren in Anwesenheit von Sauerstoff werden Carboxygruppen in den Polymeren gebildet. Deren Konzentration kann durch potentiometrische Titration bestimmt werden. Da sich auch strahlenmodifizierte Fluorpolymerpulver von Wasser schlecht benetzen lassen, wurden verschiedene wasrige Dispersionsmittelgemische untersucht. Die Qualitat der Dispersionen wurde mittels Partikelgrosenanalyse gepruft. Es wurde festgestellt, das sich hierfur ein Gemisch aus 50 Vol.-% Ethanol und 50 Vol.-% Wasser besonders gut eignet. Die wesentlichen Vorteile gegenuber der bisher eingesetzten N,N-Dimethylacetamid-Losung bestehen darin, das die Herstellung dieses Ethanol/Wasser-Gemisches mit einem geringen Zeitaufwand verbunden ist und die Blindwerte auch bei langfristiger Lagerung niedrig und stabil bleiben.