Mobility of Polymers in Films Thinner than Their Unperturbed Size

Dewetting of polystyrene films thinner than the end-to-end distance of the molecules on glass substrates as a function of film thickness (h) and temperatures was investigated. The density of the films was lower than in the bulk and decreased with decreasing h. This caused an increase of the mobility of the molecules with decreasing h. It is suggested that these effects result from an enlargement of the number of inaccessible sites caused by segregation of the molecules as h decreases.