Nanofishing of a Single Polymer Chain: Temperature-Induced Coil-Globule Transition of Poly(N-isopropylacrylamide) Chain in Water

The nanofishing of a telechelic thiol-terminated poly(N-isopropylacrylamide) (PNIPAM) single polymer chain from an Au (111) substrate in aqueous solution is investigated by atomic force microscopy. The obtained force-extension curves show two typical profiles: one is in good agreement with a so-called worm-like chain model, whereas the other is characterized by a Rayleigh-Plateau constant force. The appearance of the force plateau region is in agreement with the theoretical predictions of a pearl-necklace model. For the first time, the temperature-dependent interfacial free energy is obtained between PNIPAM and water, and it is found that it is the cause of the lower-critical-solution-temperature-type phase transition seen in PNIPAM/water system.