Simulation of random copolymers at selective interfaces and of cross-linked polymer blends

Summary We have investigated two complex statistical systems where the interfacial properties of a two-phase polymer system can be controlled. Using the bond fluctuation model (BFM) we have first studied the adsorption behavior of random copolymer chains at a single selective interface separating two phases. We found a new regime where the adsorbed chains extend in a brush-like fashion perpendicular to the interface as predicted from scaling arguments. We have extended our simulation model to investigate the influence of cross-linking on the phase behavior of polymer blends consisting of A- and B- chains. Here very large lattices are necessary to avoid finite size effects due to the network superstructure on large scale. A large cubic lattice consisting of 400 x 400 x 400 sites was sliced into 64 parts to allow for parallelization. Here we equilibrated 40 000 chains of length N = 100 before starting cross-linking under conditions without AB-interactions with different cross-link densities. Investigating the network topology we found an effective chemical dimension larger than three in agreement with previous investigations on smaller systems. This differs strongly from a simple homogeneous structure such as a diamond topology. Switching on the AB-interaction between the different chains within the network results in the formation of A- and B- enriched components, i.e. to microphase separation. The sizes of these regions axe much bigger than expected from a homogeneous network approach. The structure factor S(k) shows at intermediate wave numbers k a k -4-behavior, in contrast to the k -2-behavior expected from simplified models.