High Performance Computing in Science and Engineering 2000

Using large scale computer simulations we have investigated the interplay between single chain dynamics and the kinetics of phase separation in a symmetric binary polymer blend. In the framework of a coarse grained lattice model the bond fluctuation model on a three dimensional lattice we monitor the growth of concentration fluctuations after a quench from the one phase region into the miscibility gap. Chains of 64 effective segments are simulated in a cell of linear dimension L = 160, i.e., each simulation box contains 256 000 particles. The growth rate of composition fluctuations is averaged over 64 realizations of the temperature quench. The simulation results are compared to dynamic mean field theory without any adjustable parameter. Two theoretical approaches have been investigated: dynamical self--consistent field theory and external potential dynamics. The quantitative comparison between simulation and theory reveals the pronounced influence of the single chain dynamics on the dynamics of collective variables. A Rouse-like single chain dynamics can be incorporated into the dynamical self--consistent field theory via a non-local Onsager coefficient. The external potential dynamics results in Rouse-like dynamics without the need of a non-local Onsager coefficient. Moreover, the latter method is about an order of magnitude computationally faster than the dynamic self--consistent field theory.