It has been known that pre-adsorbed polymers on a solid surface can block some adsorption sites for a post-added polymer on the same substrate. If the charge of pre-adsorbed polymer is the same as that of post-adsorbed polymer, the repulsion force between these two polymers will change not only the polymer adsorption amount but also the conformation and the properties of the polymer on the Substrate. The site blocking effect is a possible mechanism in many commonly used flocculation programs. However, no research has been able to confirm the proposed theory of its effects on adsorbed polymer conformation. This work reports, for the first time, detailed information regarding the effects of site blocking on an adsorbed polymer's conformation using scanning probe Microscopy. Using both polymers and nanoparticles as site blocking additives, experiments were performed on single cationic polyacrylamide polymers. This work illustrates that the increased thickness in adsorbed polymer layers, reported by previous researchers, is due to a dramatic increase in the tail portion of the adsorbed polymer. The previously postulated increase in adsorbed polymer loop lengths was not present in these experiments. (c) 2008 Elsevier Inc. All rights reserved.