Influence of chain length on the interface width of an incompatible polymer blend

The interface width between polystyrene and poly-(methyl methacrylate) has been determined by neutron reflectometry as a function of molecular weight. It changes with molecular weight between $3.3\;{\rm nm}$ and $5.5\;{\rm nm}$ in the investigated range. The molecular-weight dependence is consistent with a mean-field theoretical description of the interface width of incompatible polymer blends. The determination of the interface width between incompatible polymers thus provides a means to obtain accurately the segment interaction parameter for polymer blend systems, which are otherwise difficult to determine. Results are compared with other experiments for this blend system