Direct observation of reptation at polymer interfaces

ALTHOUGH the diffusion of polymer chains in the liquid state can be described over long distances by classical diffusion laws, chain entanglements make a description of the short-range behaviour more complex. In the standard 'reptation' model 1,2 the polymer chains are considered to move in a curvilinear manner along their own contours, exhibiting snake-like motion through the entangled sea of surrounding molecules. This model successfully explains many observations 3–13 , yet no direct evidence for reptative motion has been reported. Here we describe the observation of reptation of molecules across the interface between two types of partially deuterated polystyrene polymers. The time evolution of the hyd-rogen and deuterium profiles, determined by dynamic secondary-ion mass spectrometry, can be explained only on the basis of a reptation model. Our results demonstrate that, despite being inevit-ably simplified, the description of polymer diffusion in terms of reptation is essentially correct.