• S. Ok, M. Steinhart, A. Şerbescu, C. Franz, F. V. Chávez, K. Saalwächter.
  Confinement Effects on Chain Dynamics and Local Chain Order in Entangled Polymer Melts.
  Macromolecules 43, 4429-4434 (2010). DOI 10.1021/ma1003248.

  Abstract

  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 and coworkers.

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