Segmental dynamics near the chain end of polystyrene in its ultrathin films: A study by single-molecule fluorescence de-focus microscopy

Rotational motion of fluorophores chemically attached to polystyrene chain-ends in ultra-thin films on solid substrates was studied by single-molecule fluorescence de-focus microscopy. The collective feature of the rotational motion was found and evidenced by the sharp change of the population of fluorophores undergoing rotational motion within a very narrow temperature range (named as the changing temperature, T _c). The T _c value was found to depend on film thickness and interfacial chemistry and the variation of the T _c value is also dependent on the molecular weight of the polymer. The results demonstrate that the spatial confinement effect enhances the segmental mobility near the polymer chain-ends while the interfacial attraction restricts the segmental motion inside the thin film.