  Anisotropic shear relaxation is an interesting but rarely discussed issue in
polymer dynamics under confinement [Abberton et al., Macromolecules, 48, 7631,
2015]. According to the earlier study of bead spring simulations for an
unentangled polymer melt confined between two flat plates, the shear relaxation
modulus taken perpendicular to the interface is accelerated by decreasing the
distance between plates, whereas the parallel component is unchanged. This
study observed similar anisotropic shear relaxation for entangled polymer melts
under confinement in multi-chain slip-link simulations (primitive chain network
simulations). The analysis demonstrated that the accelerated relaxation in the
perpendicular component reflects the Rouse-type constraint release dynamics,
for which the coarsening is upper-limited by the geometry. This result suggests
a novel mechanism for anisotropic shear relaxation different from the modified
chain statistics under confinement considered for unentangled systems.
