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.