Simulational Tests of the Rouse Model

An extensive review of literature simulations of quiescent polymer melts is given, considering results that test aspects of the Rouse model in the melt. We focus on Rouse model predictions for the mean-square amplitudes <(X-p(0))(2)> and time correlation functions < X-p(0)X-p(t))> of the Rouse mode Xp(t). The simulations conclusively demonstrate that the Rouse model is invalid in polymer melts. In particular, and contrary to the Rouse model, (i) mean-square Rouse mode amplitudes <(X-p(0))(2)> do not scale as sin(-2) (p pi/2N), N being the number of beads in the polymer. For small p (say, p <= 3) <(X-p(0))(2)> scales with p as p(-2); for larger p, it scales as p(-3). (ii) Rouse mode time correlation functions < X-p(t)X-p(0))> do not decay with time as exponentials; they instead decay as stretched exponentials exp(-alpha t(beta)). beta depends on p, typically with a minimum near N/2 or N/ 4. (iii) Polymer bead displacements are not described by independent Gaussian random processes. (iv) For p not equal q, < X-p (t) X-q (0)> is sometimes non-zero. (v) The response of a polymer coil to a shear flow is a rotation, not the affine deformation predicted by Rouse. We also briefly consider the Kirkwood-Riseman polymer model.

Automated summary

An extensive review of literature simulations of quiescent polymer melts reveals that the Rouse model is invalid in polymer melts. The simulations demonstrate that mean-square amplitudes and time correlation functions of the Rouse mode in polymer melts do not match the predictions of the Rouse model. Additionally, polymer bead displacements in polymer melts are not accurately described by independent Gaussian random processes.