Uncrossability constraints in mesoscopic polymer melt simulations: Non-Rouse behavior of C120H242

An important feature of a melt of long polymers is that the bonds of the ch ains cannot cross each other. This seemingly simple fact has a great impact on the long time dynamics and rheology of the material. In this paper an a lgorithm is described that explicitly detects and prevents bond crossings i n mesoscopic simulations of polymers. The central idea is to view the bonds as slippery elastic bands which can become entangled. The method is applie d to a simulation of a coarse-grained melt of C120H242, in which each chain is represented by six blobs. The long time dynamics and zero-shear rate rh eology are investigated and the relative importance of uncrossability and c hain stiffness is established. As a result of the uncrossability of the cha ins, we observe a subdiffusive exponent in the mean square displacement of the chains, a stretching of the exponential decay of the Rouse mode relaxat ions, an increase of relaxation times associated with large scales, and a s lowing down of the relaxation of the dynamic structure factor. These result s are in agreement with results from previous microscopic molecular dynamic s simulations. Finally, an increased viscosity as compared to the Rouse mod el is observed, which is attributed to slowly decaying interchain stress co mponents. (C) 2001 American Institute of Physics.