Short Time Behavior in de Gennes’ Reptation Model

To establish a standard for the distinction of reptation from other modes of polymer diffusion, we analytically and numerically study the displacement of the central bead of a chain diffusing through an ordered obstacle array for times t , O sN2d. Our theory and simulations agree quantitatively and show that the second moment approaches the t1y4 power law (often viewed as a signature of reptation) only after a very long transient and only for long chains (N . 100). Our analytically solvable model furthermore predicts a very short transient for the fourth moment. This is verified by computer experiment. [S0031-9007(97)02510-6]