Controlling the adsorption of single poly(styrenesulfonate) sodium on NH3+-modified gold surfaces on a molecular scale

Densely packed amino-terminated monolayers of high degree of order were for med by self-assembly of amino-terminated alkanethiols. Negatively charged p oly(styrenesulfonate) (PSS) molecules were electrostatically adsorbed on th e NH3+ surface. The density of single PSS molecules on the surface was regu lated by carefully controlling its concentration as well as adjusting the t ime in the dilute solution. Dynamic force microscopy in "tapping mode" was applied to map PSS polymers with molecular resolution. The lateral dimensio ns (15-25 nm) and heights (0.5-1.0 nm) of the adsorbed PSS macromolecules a re in fair agreement with the theoretical diameters and the experimental es timations. The average area, volume, and charge density of single PSS patch es absorbed on a positively charged surface is 378 nm(2), 122 nm(3), and 0. 90e(-)/nm(2), respectively. The structure of adsorbed PSS polymers was disc ussed down to the molecular scale. The observations support the patch charg e model of flocculants.