Evaluation of surface modification by electrokinetic measurements

For along time, measurements of the electrokinetic potential have been used in colloid chemistry mainly for the calculation of electrostatic interaction forces in colloid systems. Moreover, electrokinetic measurements are increasingly successful in characterising solid surfaces. Studies of the effects of pH, surface-active agents, etc. on the electrokinetic potential give valuable information about the nature of solid surfaces. According to Jacobasch [Prog. Org. Coat. 17 (1989) 115], it is possible to distinguish between dissociation and adsorption processes. We are also able to recognise chemical reactions on the surface during measurement. Electrokinetic properties of different polyformamidines should give us an idea about the chances of this method. While electrokinetic properties of colloidal particles have been widely investigated by means of electrophoresis, the electrokinetic characterisation of the surface of macroscopic specimens is still rather uncommon. Indeed, the use of a commercial electrokinetic analyser (EKA) streaming potential measurement apparatus (Anton Paar KG, Graz, Austria) allows the rapid and reproducible measurement of streaming potential, including those of plates and sheets. By means of these investigations, we are able to tackle problems of adhesion of coatings on polymers. This was already demonstrated at the influence of different finishing methods like oxygen plasma treatment or flame treatment on the surface of polypropylene rubber blends [Prog. Org. Coat. 26 (1995) 13 1; J. Adhes. Sci. Technol. 9 (1995) 327]. By creating special conditions, we succeeded in measuring streaming potentials on metal surfaces, as shown by the example of Al-sheets. With the help of these measurements, different surface treatments were determined. (C) 2002 Elsevier Science B.V. All rights reserved.