# Measurements of Polymer Diffusion Over Small Distances: A Check of Reptation Arguments

G. Reiter, U. Steiner. J. Phys. (France) II 1, 659-671 (1991)

### Abstract

We performed neutron reflectrometry (NR) and nuclear reaction analysis (NRA) measurements on interdiffusion of protonated and deuterated polystyrene films. Covering several orders of magnitude in time t and resolving interfacial widths w(t) between approximately 2 nm and 60 nm we found two successive time regimes with a crossover corresponding to the reptation time tau-d. Below tau-d we are able to approximate the interface profile quite well by two superposed error functions described by three parameters, sigma-c(t), sigma-t(t) and p(t). The two contributions are interpreted according to the Rouse and the reptation model. While the width sigma-c of the error function correlated to Rouse type motion stays almost constant, the width sigma-t of the second contribution increases with time. p(t) represents the percentage of the second contribution at the interface. It increases with time reaching 100 per cent at tau-d. An explanation is given in terms of the reptation model. The time behavior of sigma-c(t), sigma-t(t), p(t) and w(t) is discussed. tau-d and w(tau-d) are determined independently using three different methods. All results are in qualitative agreement with the reptation model.