Conformation of Cationic Polyacrylamide on Mica Studied by Single Molecule “Pulling” Technique

In this work, an improved “pulling” method using scanning probe microscopy (SPM) has been used to gain information about the conformation of an adsorbed polymer. The sequential adsorption/desorption of cationic polyacrylamide on freshly cleaved mica in deionized water was directly measured using these modified SPM experiments. Our method uses a specially etched tip which ensures only one polymer molecule is adsorbed on the cantilever tip allowing more accurate interpretation of the results. The effect of cantilever tip retraction velocity from the surface was shown to be insignificant to the measured loop length distribution. The effects of site-clocking polymer and nanoparticles on the conformation of post-adsorbed polymer were investigated. It was found that the loop length of absorbed polymer remains almost constant, but the tail length increases significantly in the presence of site blocking agents. For the first time, SPM was used to show the effects of dwell time on adsorbed polymer conformation.