Nonequilibrium tube length fluctuations of entangled polymers

We investigate the nonequilibrium tube length fluctuations during the relax ation of an initially stretched, entangled polymer chain. The time-dependen t variance sigma (2) of the tube length follows in the early-time regime a simple universal power law sigma (2) = A roott originating in the diffusive motion of the polymer segments. The amplitude A is calculated analytically both from standard reptation theory and from an exactly solvable lattice g as model for reptation and its dependence on the initial and equilibrium tu be length, respectively, is discussed. The nonuniversality suggests the mea surement of the fluctuations (e.g., using flourescence microscopy) as a tes t for reptation models. (C) 2001 American Institute of Physics.