Soft-contact Atomic Force Microscopy Imaging of Adsorbed Surfactant and Polymer Layers

The technique of atomic force microscopy (AFM) soft-imaging is outlined with respect to characterizing the adsorption of surfactants and polymers at the solid/liquid interface. This method utilizes the electrostatic and steric repulsion forces between the scanning probe and the sample to allow sensitive placement of the imaging probe near to the delicate surface layer. Specifically, the mixed adsorption of sodium dodecylsulfate (SDS) and poly(vinyl pyrrolidone) (PVP) on graphite is examined. Unlike the adsorbed layer in a solution of either component, the adsorbed layer in the mixture does not cover the substrate uniformly until equilibrium is reached (often hours later). The interesting kinetic and coverage effects observed are significant to the many applications reliant on adsorption from polymer-surfactant mixtures, especially to the flocculation of dispersions.