Elasticity of single polyelectrolyte chains and their desorption from solid supports studied by AFM based single molecule force spectroscopy

AFM based single molecule force spectroscopy was used for the investigation of single polyelectrolyte chains. Namely, the elasticity of polyvinylamine chains and their desorption from solid surfaces was studied as a function of the polymer's charge density and electrolyte concentration. Experimental force-distance profiles were fitted by the wormlike chain model, including elastic contributions arising from the stretching of bond angles and coval ent bonds. It was found that, under the high stretching forces which can be applied in the AFM experiments, the bending rigidity of polyelectrolyte ch ains (as described by the persistence length) is significantly lower than p redicted by Odijk-Skolnick-Fixman (OSF) theory. Furthermore, the desorption force of single physisorbed polymer chains from negatively charged silica surfaces was determined. In addition to the electrostatic interaction betwe en polymer and substrate, which depends linearly on the Debye screening len gth and the polymer's line charge density, a constant nonelectrostatic cont ribution to the desorption force was observed.