Large-Scale Diffusion of Entangled Polymers along
Nanochannels
- Publication date
- Publisher
Abstract
Changes in large-scale polymer diffusivity
along interfaces, arising
from transient surface contacts at the nanometer scale, are not well
understood. Using proton pulsed-gradient NMR, we here study the equilibrium
micrometer-scale self-diffusion of poly(butadiene) chains along ∼100
μm long, 20 and 60 nm wide channels in alumina, which is a system
without confinement-related changes in segmental relaxation time.
Unlike previous reports on nonequilibrium start-up diffusion normal
to an interface or into particulate nanocomposites, we find a reduction
of the diffusivity that appears to depend only upon the pore diameter
but not on the molecular weight in a range between 2 and 24 kg/mol.
We rationalize this by a simple volume-average model for the monomeric
friction coefficient, which suggests a 10-fold surface-enhanced friction
on the scale of a single molecular layer. Further support is provided
by applying our model to the analysis of published data on large-scale
diffusion in thin films