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Salt effect on cationic polyacrylamide conformation on mica studied by single molecule "pulling" with scanning probe microscopy.

The effect of salts on adsorbed polyelectrolyte conformations has been studied extensively over the past three decades. Previous researchers have proposed that increasing salt concentration results in larger loops and tails for weak polyelectrolytes adsorbed on a surface. However, no experimental verification of this theory has been published. In this work, we present experimental verification acquired by "pulling" single molecules of a polyelectrolyte from a mica surface using a scanning probe technique. We also present a new method for analyzing changes in adsorbed polymer tail lengths. We demonstrate that increasing solution salt concentration correlates with both loop and tail lengths of an adsorbed low charge density cationic polyacrylamide on a mica substrate.