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 nonlin ear elastic response is shown to be present hundreds of nanometers above th e 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 an d Kuhn lengths of approximately 3 and 4 Angstrom, respectively. The entropi c models reveal that the polymer chains are stretched to 80-90% of their co ntour length before the attachment to the tip is ruptured.