Large-scale diffusion of entangled polymers along nanochannels

Confinement-induced changes in polymer mobility are still under active discussion. For weakly interacting poly(butadiene) chains in 100 $\mu$m long, 20 and 60 nm wide channels in anodic Al2O3 [1], we here report on the study of the large-scale pore-averaged self diffusion on a $\mu$m scale by 1H pulsed-gradient NMR. We find weak indications of an acceleration due to surface-induced disentanglement [2]. Unlike previous reports on polymer diffusion into particle nanocomposites of similar confinement scale [3], or start-up diffusivities out of even thinner films [4,5], we find an MW and temperature independent reduction of diffusivity that is solely determined by the confinement size. We rationalize this trend by a simple volume-average model, which suggests a 20-fold surface-enhanced monomeric friction on the scale of the packing length, which can be compared to a factor of 300 that our model predicts for comparable thin-film data of poly(styrene) on silica [4].\\[4pt] [1] S. Ok et al.{\em Macromolecules} {\bf 43} (2010) 4429;\\[0pt] [2] D.~M. Sussman et al. {\em Macromolecules} {\bf 47} (2014) 6462;\\[0pt] [3] J. Choi et al. {\em ACS Macro Lett.} {\bf 2} (2013) 485;\\[0pt] [4] B. Frank et al. {\em Macromolecules} {\bf 29} (1996) 6531;\\[0pt] [5] X. Zheng, et al. {\em Phys. Rev. Lett.} {\bf 74} (1995) 407