Segment diffusion in polymers confined in nanopores: A fringe-field NMR diffusometry study

The dynamics of polymer chains confined in artificial tubes formed by the p ores of a nanoporous material should display all the features predicted by the reptation model, provided that the polymer/wall interaction does not le ad to adsorption effects. We have studied the segment diffusion behavior of linear polyethyleneoxide in the molten state in pores of well characterize d cross-linked polyhydroxyethylmethacrylate matrices. These "semi-interpene trating networks" were prepared in such a way that (10+/-2) nm thick cylind rical pores completely filled with polyethyleneoxide were produced. The mea suring technique was fringe-field NMR diffusometry. The results are compati ble with a power law for the mean squared displacement, [r(2)] proportional to t(-0.4+/-0.1) M-w(-0.8+/-0.2), where t is the diffusion time and M-w, i s the weight average molecular mass. This is to be compared with the limiti ng law [r(2)] proportional to t(-1/2) M-w(-1/2) predicted by de Gennes, Doi , and Edwards for region III, that is, tau(R)much less than t much less tha n tau(d) Of the tube/reptation model. In the frame of the experimental accu racy the conclusion is that the reptative diffusion mechanism applies to li near polymer chains of sufficient length relative to the diameter of the co nfining pores.