Adsorption of poly(propylene imine) dendrimers on glass. An interplay between surface and particle properties

The adsorption behavior of positively charged poly(propylene imine) dendrim ers on glass has been studied by scanning angle reflectometry as a function of generation, pH, and ionic strength. The results indicate that the adsor ption is controlled by properties of both the dendrimers (size and charge) and the surface layer (distribution of glass surface sites). At constant pH and ionic strength the collector properties remain the same, and the adsor ption scales with dendrimer size. Because of the limited number of glass su rface sites there is only 15% surface coverage at maximum. Adsorption incre ases with decreasing pH and increasing ionic strength, and the effect of pH is much more pronounced for the smaller dendrimers. To explain the adsorpt ion results, not only the size and charge of the dendrimer have to be taken into account, but also the charge density and the roughness of the surface . This implies that the dendrimer size is comparable to the characteristic length scale of the surface roughness.