Solvent effects on single polymer chain physics investigated by atomic force microscopy

Nanofishing, a method to stretch a single polymer chain adsorbed on a substrate with its one end by picking it at another end using atomic force microscope probe enabled us to investigate the statistical properties of single polymer chains. A force-extension curve obtained for a single polystyrene chain in a Theta solvent (cyclohexane) showed a good agreement with a worm-like chain model, and thus gave microscopic information about entropic elasticity. Solvent effects on polymer chain conformations were the main issue of this paper. The temperature dependence of persistence length in cyclohexane was examined at a single polymer basis, which was almost comparable with a simple Flory's lattice model. The coil-strand transformation realized in a poor solvent (water) was also discussed.