Hydrophobicity measurements of microfiltration and ultrafiltration membranes.

A method for the determination of the hydrophobicity of membrane materials is developed. The advantage of this method over existing methods is that it is not influenced by the presence of the pores. A piece of the membrane material is submerged horizontally in a liquid with surface tension L. Hydrophobicity is expressed in terms of d, the surface tension at which an air bubble brought into contact with the top surface of the membrane has a 50% chance of detaching from the surface. Values of d are expected to be 2-4 mN/m higher than critical surface tension (c) values found in the literature. For polypropylene, PTFE and polydimethylsiloxane membranes, a good agreement was found between d and c values. Poly (vinylidene fluoride), polysulfone and polyethersulfone membranes appeared to be more hydrophilic than was expected on the basis of the literature c values for the polymers. Using X-ray photoelectron spectroscopy, constituents that are not present in the pure polymer have been found in the surface of some membranes. These constituents and the production techniques are shown to influence the hydrophobicity of the membranes investigated