J. Phys. II France
Volume 1, Number 6, June 1991
Page(s) 659 - 671
DOI: 10.1051/jp2:1991197
J. Phys. II France 1 (1991) 659-671

Measurements of polymer diffusion over small distances. A check of reptation arguments

G. Reiter1 and U. Steiner2

1  Max Planck Institut für Polymerforschung, P.O.B. 3148, 6500 Mainz, F.R.G.
2  Department of Polymer Research, Weizmann Institute of Science, Rehovot 76100, Israel

(Received 13 December 1990, accepted 4 March 1991)

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 $\tau_{\rm d}$. Below $\tau_{\rm d}$ we are able to approximate the interface profile quite well by two superposed error functions described by three parameters, $\sigma_{\rm c}(t)$ and $\sigma_t(t)$, p(t). The two contributions are interpreted according to the Rouse and reptation model. While the width $\sigma_{\rm c}$ 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 $\tau_{\rm d}$. An explanation is given in terms of the reptation model. The time behavior of $\sigma_{\rm c}(t)$, $\sigma_t(t)$, p(t) and w(t) is discussed. $\tau_{\rm d}$ and $w(\tau_{\rm d})$ are determined independently using three different methods. All results are in qualitative agreement with reptation model.

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