AFM evidence of Rayleigh instability in single polymer chains

We present experimental evidence of the Rayleigh-Plateau instability of a single chain in poor solvent conditions using single molecule force microscopy. Poly(N-isopropylacrylamide) (PNIPAM) and poly(ethylene oxide) (PEO) are adsorbed onto silicon nitride surfaces in various solutions corresponding to poor and good solvent conditions. In good solvent conditions, the force-separation profile is identical to that described previously and attributed to the elastic stretching of single polymer chains. However, in poor solvent conditions, we see a dramatically different force profile, characterized by steps or plateaus of constant force. These plateaus represent the "pull-out" of chain segments from collapsed globules of polymer collected at each of the separating surfaces. A statistical analysis of the large number of force profiles collected indicates that these plateaus are quantized, suggesting pull-out of several chains of different length. Moreover, the frequency of the steps suggests that we can distinguish pulled loops from pulled tails.