Cell dynamics simulations of microphase separation in block copolymers

Cell dynamics simulations of ordered structures formed in diblock copolymer melts were performed to investigate the effects of simulation parameters o n the morphological features and kinetics of ordering from the initial diso rdered state. We show that sphere, cylinder, lamellar, and bicontinuous str uctures can all be simulated with an appropriate choice of system parameter s. The simulation parameters are related to the expansion parameters in the Landau free energy in the Cahn-Hilliard-Cook equation, of which the cell d ynamics equations are a coarse-grained discretization. The extent of segreg ation is found to increase as the effective diffusion coefficient decreases . It is shown that the magnitude of the long-range repulsive contribution t o the free energy has to be defined within certain limits to produce morpho logies that resemble those observed experimentally. The formation of ordere d structures is found to be quicker, as expected, for deeper quenches, whic h also produce more strongly segregated structures. Addition of random ther mal noise proves to be essential to generate spherical structures, formed i n the high-temperature ordered phase region. Thermal noise also acts to inc rease the ordering kinetics.