(338v) Computational Studies of the Order-Disorder Transition in Block-Random Copolymers

Block copolymer (BCP) thin films with lamellar nanostructures oriented perpendicular to the substrate surface are a potential alternative to photolithography for patterning nanoscale features. Cyclization has been shown to reduce BCP feature size and improve thin film stability, but orientation control also is needed for lithography. Here, we use dissipative particle dynamics (DPD) simulations to study the relative stability of perpendicular (vs. parallel) lamellae formed by cyclic and linear BCPs. To mimic experiments, BCP chains are confined between a substrate (2D lattice of DPD beads), and a “gas” bath (DPD beads). With non-selective surface interactions (no preferential interactions for either blocks on the "gas" and the substrate side), both linear and cyclic BCPs form perpendicular lamellae as expected. To test relative stability of perpendicular lamellae, we increased the substrate surface preference in a series of steps for one of the blocks until the lamellae oriented parallel to the substrate and found that perpendicular lamellae are more stable for linear BCPs than for cyclic BCPs. These findings suggest that the substrate neutrality condition for perpendicular lamellae is less stringent for linear BCPs than for cyclic BCPs. We seek to understand the thermodynamics behind these differences based on near-surface chain orientations and free energy calculations.