Single Polymer Chain Elongation by Atomic Force Microscopy

The elastic deformation of single polystyrene- b -poly-2-vinylpyridine chains from spun cast films was investigated by atomic force microscopy. A nonlinear elastic response is shown to be present hundreds of nanometers above the bulk surface. The length of the elastic response monotonically increases with molecular weight of the polymer. These nonlinear elastic responses are fit to wormlike chain and freely joined chain models giving persistence and Kuhn lengths of approximately 3 and 4 Å, respectively. The entropic models reveal that the polymer chains are stretched to 80−90% of their contour length before the attachment to the tip is ruptured.