Polydispersity effects on diffusion in polymers: Concentration profiles of d‐polystyrene measured by forward recoil spectrometry

Abstract Forward recoil spectrometry is shown to be a useful technique for measuring diffusion of d‐polymer chains in h‐polymer melts. Concentration profiles of a deuterated diffusing species may be determined with a depth resolution of 80 nm and a sensitivity of 0.1 vol % d‐polymer in h‐polymer. Consequently diffusion coefficients as small as 10 −16 cm 2 /s can be readily measured. If polymer chains diffuse by a reptation mechanism, the concentration profile ø( x ) of diffusing polydisperse polymer should be quite different from ø m (x ), the Fickian solution, which one obtains for monodisperse polymer. This idea was tested by measuring ø( x ) of polydisperse d‐polystyrene (d‐PS) diffusing into h‐PS. The results are in excellent agreement with the ø( x ) predicted from the reptation model and the experimentally determined molecular weight distribution.