  The tube model is a central concept in polymer physics, and allows to reduce
the complex many-filament problem of an entangled polymer solution to a single
filament description. We investigate the probability distribution function of
conformations of confinement tubes and single encaged filaments in entangled
semiflexible polymer solution. Computer simulations are developed that mimic
the actual dynamics of confined polymers in disordered systems with topological
constraints on time scales above local equilibration but well below large scale
rearrangement of the network. We observe the statistical distribution of
curvatures and compare our results to recent experimental findings.
Unexpectedly, the observed distributions show distinctive differences from free
polymers even in the absence of excluded volume. Extensive simulations permit
to attribute these features to entropic trapping in network void spaces. The
transient non-equilibrium distributions are shown to be a generic feature in
quenched-disorder systems on intermediate time scales.
