Conformation of a single polyacrylamide molecule adsorbed onto a mica surface studied with atomic force microscopy

We have studied the adsorption of a single polyacrylamide chain onto a freshly cleaved mica surface from a good solvent by force spectroscopy using a custom-built force prober. The polymer chain was covalently attached to the AFM tip at one end. The polymer loop lengths were deduced by measuring the distance between desorption events during the retraction of the tip from the surface. The loop length distribution obtained was found to obey a power law characteristic for the semidilute regime. We claim that this is due to the confinement of the polymer chain between the tip and the surface during the adsorption.