S. Ok, M. Steinhart, A. Şerbescu, C. Franz, F. V. Chávez, K.
Confinement Effects on Chain Dynamics and Local Chain
Order in Entangled Polymer Melts.
Macromolecules 43, 4429-4434
(2010). DOI 10.1021/ma1003248.
We investigate the dynamics and local (tube-induced) residual orientation of
entangled polymer chains in a time range beyond the entanglement time in
geometric confinement by neutral (nonabsorbing) interfaces. We present NMR data
on two different model systems, i.e., soft spherical confinement of moderately
entangled poly(dimethyl siloxane) (90 kDa) in emulsion droplets in the 200-900
nm range, and hard confinement of highly entangled poly(butadiene) (87 kDa) in
cylindrical nanochannels with diameters of 20 and 60 nm in self-oderered anodic
aluminum oxide. We address the problem of obtaining reproducible results in both
cases, where droplet size reproducibility and polydispersity, and
infiltration-time dependent changes, respectively, are important issues. In both
cases, we find significantly enhanced local chain order with indications of
inhomogeneity in the investigated systems. These results suggest the occurrence
of orientation effects originating from the confining interfaces that propagate
several nanometers into the polymer melt. A comparison of the two systems
suggests that the entanglement separation governs the lengthscale of the
phenomenon. The effect, that is observed in terms of increased residual dipolar
couplings, appears related to the "corset effect" recently reported by Kimmich