Polyelectrolyte brushes and polyelectrolyte adsorption lasers

The structure of brushes and adsorption layers of polyelectrolytes containing strong and weak groups is analysed, using both a numerical self-consistent-field (SCF) model and approximate analytical expressions, The latter are based upon a local electroneutrality approximation (brushes) or upon a mutual compensation of the adsorbed polymer charge and the diffuse double layer charge (adsorption layers); under most conditions excellent agreement with the SCF model is obtained. Brushes with strong groups are relatively compact at high ionic strength and the brush thickness increases monotonously as the salt concentration is reduced. On the other hand, in ''weak'' brushes the root-mean-square thickness passes through a maximum as a function of the salt concentration, because the weak groups will discharge themselves at low; ionic strength. Such a charge regulation is impossible for strong groups. For adsorption layers, the adsorbed amount is high when the polymer is weakly charged and it decreases as the polymer charge is increased. This general trend is the same for strong and weak groups. However, weak groups can again adjust their charge. As a result, at intermediate charge densities their degree of dissociation is much lower than in the bulk solution; consequently the adsorbed amount is much higher than for strong groups.