Ring and Linear Copolymer Blends under Confinement

The behavior of dense mixtures of two topologically different diblock copolymer (CP) chains, viz., linear (L)-CP and ring (R)-CP of the same molecular weight, which form lamellae is studied under confinement by two nonselective substrates. The effect of varying interaction strength between L-CP and R-CP from purely repulsive (demixed state) to weakly attractive (mixed state) on the morphology, domain size, chain conformations, and distribution of chains in the film is investigated. In the demixed state, collective structure factor S(q) shows a split of the predominant peak indicating the presence of two dominant length scales, while there is only one predominant peak in the mixed state, and hence a lamellar structure with single domain size. We show that the peak position q* of S(q) can be varied with the L/R interaction strength and thus allows one to control domain size by tuning L/R interaction strength without altering the chain size. We further characterize the chain size and illustrate that this domain size variation is a consequence of the variation in the size of L-CPs. Furthermore, results on the average instantaneous shape of R/L-CP reveal that their shapes are very different both in bulk and near the substrate, and R-CP assumes an oblate shape near the substrate. This shape/size difference leads to the segregation of R-CPs near the polymer-substrate interface and hence a relatively higher density of R-CPs at the interface.