Unravelling the surface composition of symmetric linear-cyclic polymer blends

We perform molecular dynamics computer simulations of free-standing films of symmetric binary linear-cyclic polymer mixtures at equimolar composition. We show that the density of linear polymers at the free-surface is enhanced with respect to the bulk value for short chains, but it is depleted for long chains. Our findings suggest that the enhancement of the composition of linear chains reported for polystyrene polymer blends might hold in a more extended composition range than the one considered in previous experiments at the free surface. Focusing on the equimolar regime of the two polymer species with the identical chain length allows us to safely conclude that the observed surface deviations from the bulk are driven by the topological differences between the two polymer species, and rule out any role played by the different concentration of the two polymer species.