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

Abstract

The dynamics of polymer chains confined in artificial tubes formed by the pores of a nanoporous material should display all the features predicted by the reptation model, provided that the polymer/wall interaction does not lead to adsorption effects. We have studied the segment diffusion behavior of linear polyethyleneoxide in the molten state in pores of well characterized cross-linked polyhydroxyethylmethacrylate matrices. These ''semi-interpenetrating networks'' were prepared in such a way that (10Ϯ2) nm thick cylindrical pores completely filled with polyethyleneoxide were produced. The measuring technique was fringe-field NMR diffusometry. The results are compatible with a power law for the mean squared displacement, ͗r 2 ͘ ϰt Ϫ0.4Ϯ0.1 M w Ϫ0.8Ϯ0.2 , where t is the diffusion time and M w is the weight average molecular mass. This is to be compared with the limiting law ͗r 2 ͘ϰt Ϫ1/2 M w Ϫ1/2 predicted by de Gennes, Doi, and Edwards for region III, that is, R ӶtӶ d of the tube/reptation model. In the frame of the experimental accuracy the conclusion is that the reptative diffusion mechanism applies to linear polymer chains of sufficient length relative to the diameter of the confining pores.

Comment on “Neutron scattering study of the dynamics of the polymer melt under nanoscopic confinement” [J. Chem. Phys. 131, 174901 (2009)]

“…The results were shown to be compatible with the tube/reptation model. 13,15 However, the dimension of the topological constraints evaluated from these data turned out to be much larger than the values usually reported in the literature for this model. Based on the field-gradient NMR diffusometry data, no substantial confinement effect beyond restriction to the pores can be stated for translational fluctuations.…”

“…The strand diameter was estimated with different methods including electron microscopy. [13][14][15][16] The value for the samples studied in Ref. 1 is about 10 nm.…”

Anomalous Dielectric Relaxation in Binary Mixtures of Mesogenic Solvent/Non-Mesogenic Solute

“…Subdiffusion reflects an existence of some traps for diffusing particle in a system, thus it can be expected in some complex and heterogeneous liquids as well as in homogeneous and isotropic liquids placed in a matrix of complex geometry. The list of systems displaying a subdiffusive behavior is quite long and among them, one can quote percolative [7], porous [8], and polymeric [9,10] systems as well as some transport processes such as the charge transport in amorphous semiconductors [11][12][13][14], for example.…”

Spatio-temporal anomalous diffusion in heterogeneous media by nuclear magnetic resonance

“…Lz, 87.64.kj, 61.05.Qr, Anomalous diffusion (AD), that predicts the meansquare displacement (MSD) of a diffusing particle to grow nonlinearly in time, [x(t) − x(0)] 2 ∝ t ν (with ν = 1), is a property of many complex systems and its related phenomena have been observed in various physical fields [5,8,14,16,17]. As shown by Metzler and coworkers [10], the features of AD can be described using fractional calculus.…”