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

G. Reiter; U. Steiner

doi:doi:10.1051/jp2:1991197

Numéro		J. Phys. II France Volume 1, Numéro 6, June 1991


Page(s)		659 - 671
DOI		https://doi.org/10.1051/jp2:1991197

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)

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 $\tau_{\rm d}$ . 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.