Interfacial diffusion of a single cyclic polymer chain.

Lateral diffusion of cyclic polystyrene at the interface between fused silica and dichloromethane is investigated at the single-molecular level. Narrowly distributed cyclic polystyrene (c-PS) of high purity with molecular weights spanning nearly an order of magnitude is prepared via atom transfer radical polymerization (ATRP) and Cu-catalyzed azide/alkyne cycloaddition (CuAAC) click reaction. The diffusion coefficients (D) of c-PS and its linear analogue (l-PS) on the surface are measured by fluorescence correlation spectroscopy (FCS). The diffusion coefficient of c-PS is discovered to have an inverse dependence on molecular weight, D ∼ M-1, in contrast to the case of linear polystyrene, which reproduces a stronger molecular weight dependence, D ∼ M-3/2. The slower interfacial motion of cyclic chains is attributed to their stronger binding to the surface and more importantly, the unique surface diffusion mechanism due to the absence of free chain ends.