Spinodal decomposition in a binary polymer mixture: Dynamic self-consistent-field theory and Monte Carlo simulations - art. no. 041804

We investigate how the dynamics of a single chain influences the kinetics o f early stage phase separation in a symmetric binary polymer mixture. We co nsider quenches from the disordered phase into the region of spinodal insta bility. On a mean field level we approach this problem with two methods: a dynamical extension of the self-consistent-field theory for Gaussian chains , with the density variables evolving in time, and the method of the extern al potential dynamics where the effective external fields are propagated in time. Different wave vector dependencies of the kinetic coefficient are ta ken into account. These early stages of spinodal decomposition are also stu died through Monte Carlo simulations employing the bond fluctuation model t hat maps the chains-in our case with 64 effective segments-on a coarse grai ned lattice. The results obtained through self-consistent-field calculation s and Monte Carlo simulations can be compared because the time. length, and temperature scales are mapped onto each other through the diffusion consta nt, the chain extension, and the energy of mixing. The quantitative compari son of the relaxation rate of the global structure factor shows that a kine tic coefficient according to the Rouse model gives a much better agreement than a local, i.e., wave vector independent, kinetic factor. Including fluc tuations in the self-consistent-field calculations leads to a shorter time span of spinodal behavior and a reduction of the relaxation rate for smalle r wave vectors and prevents the relaxation rate from becoming negative for larger values of the wave vector. This is also in agreement with the simula tion results.