Zeta potential measurements on polyelectrolyte multilayers

Abstract

Consulta en la Biblioteca ETSI Industriales (8629)

[EN] The main object of this thesis is to study the surface charge of a polyelectrolyte multilayer when new layers are being built. In order to achieve this goal, a device for zeta potential measurements by means of a rotation disk was adjusted and tested. It has been proved that the streaming potential reacts as predicted by the theory to changes on the conductivity, rotation rate and electrode distance. Two different substrates have been used. The device was first tested on a PEEK disk coated with PEI, but when building up the multilayer it was impossible to verify its proper growth. Therefore a silicon wafer was used as a substrate instead of the PEEK, since its negative charged surface is more convenient for the multilayer growth and because it allows thickness measurements by ellipsometry. A ten layer multilayer has been built on a silicon wafer, measuring the zeta potential and the thickness of each layer. The surface showed charge reverse after each layer and the zeta potential value seemed independent of the number of layers. Thickness showed typical growth of this kind of multilayer. Finally the zeta potential has been measured while a new layer was being formed. The streaming potential increased as the positive polymer was being incorporated to the multilayer. It has been possible to observe how the previous layer was neutralized and the sign of the zeta potential inverted. It has been also observed that the rate of the layer formation depends on the concentration of polymer. The higher the concentration the fastest the layer is build. This study opens the door for kinetic studies of the multilayer formation.