This work addressed the bound train fraction of an adsorbing model polyelectrolyte ((dimethylamino)ethyl methacrylate, DMAEMA), for variations in pH, which altered the relative charge densities of the polymer and substrate (silica). In addition to the weakly basic and acidic natures of the polyelectrolyte and substrate, respectively, this model system had the characteristic that adsorption was driven exclusively by electrostatic attractions. Therefore, at pH's where the polymer or the substrate was not charged, adsorption did not occur. At pH 6, which represented the extreme of a sparsely charged substrate and a densely charged polyelectrolyte with condensed counterions, the train fraction approached unity and was coverage-independent. At these conditions, the maximum bound train mass of 0.7 mg/m(2) exceeded previous reports for the maximum train mass of adsorbed nonionic polymers. At higher pH's, the substrate charge density increased while the polymer became sparsely charged. In this limit, the train fraction decreased and became coverage dependent, with loops and tails forming at crowded interfacial conditions, similar to previous observations for adsorbing nonionic polymers.