Abstract:

A molecular dynamics simulation(MD) is performed to study the phase separation of binary symmetric polymer blend systems. The blend systems comprise of two kind of polymers with equal chain length of 20 and total chain number of 1 000. By adjusting chain numbers of polymer A,  a series of volume fractions φ from 0.1 to 0.5 were obtained. Polymer chains were simulated by a coarse-grained bead-spring model. The interaction potential between monomers is purely repulsive Lennard-Jones 12-6 potential and the bond potential between neighbor monomers along the sequence of the chain is FENE potential. The collective structure factor evolving with time,  S(q,t),  is obtained by the fast Fourier transform(FFT) of the concentration fluctuation function. As the phase separation proceeds,  the maximum of the collective structure factor increase with the increase of  time. The average phase domain size R(t) keeps constant at the early stage. At the intermediate stage,  R(t) increase with the increase of  time and a scaling relation  of R(t) vs. t1/3 is observed. At the last stage of the phase separation,  R(t) is time independent again. The time evolution of polymer chain size,  as well as the coordination number of monomer is also investigated during the phase separation. All these indicate that MD simulation is an effective and advantageous method for studying the dynamics of phase separation of polymer blend systems.

Key words: Polymer phase separation;  Structure factor;  Domain Size;  Molecular dynamics simulation