Cationic electrolyte adsorption layers on hydrophilic and hydrophobic surfaces

The capillary electrokinetics method (measurements of streaming potential and current in original and hydrophobized fused quartz capillaries with radii of 5–7 μm) is employed to study the formation of adsorption layers upon contact with solutions containing a cationic polyelectrolyte, poly(diallyldimethylammonium chloride). It is shown that polyelectrolyte adsorption causes the charge reversal of both hydrophilic and hydrophobic surfaces, with a smaller amount of the substance being adsorbed on the hydrophobic than on the hydrophilic surface. The adsorption on both surfaces increases with the polymer solution concentration. The cationic polyelectrolyte adsorption on the pure quartz surface occurs mainly due to the electrostatic attraction, while, in the case of the hydrophobic surface, the contribution of hydrophobic interactions increases. The study of the layer deformability shows that, on the hydrophilic surfaces, the layer ages and its structure depends on the polymer solution concentration. On the modified surface, the deformation of even freshly formed layers is slight, which suggests that a denser layer is formed on the hydrophobic surface. In contrast to the hydrophilic surface, the polyelectrolyte is partly desorbed from the hydrophobic surface.