Thermodynamic and Kinetic Stability of Square Patterns in AB/A Blends under Square Confinement

The directed self-assembly (DSA) of block copolymers has been widely used to fabricate large-scale hexagonal-arrayed patterns. However, effective strategies for fabricating square-arrayed patterns still need to be developed. Given that the cylinders assembled by simple AB-type block copolymers typically adopt a hexagonal arrangement in the bulk, we investigate the self-assembly behavior of a blend composed of an asymmetric AB diblock copolymer and an A-homopolymer laterally confined in a square well, aiming to achieve thermodynamically and kinetically stable square-arrayed cylinders. We first use self-consistent field theory (SCFT) to determine the phase diagrams of the AB/A blends. The phase diagrams demonstrate that 4 × 4, as the largest square array of cylinders, can be stabilized by using appropriate homopolymer additives, as well as confinement sizes. Then, we combine SCFT with the string method to determine the minimum free-energy path (MFEP) between the stable square morphology and the possible metastable defective morphologies. The results show that the stability of those metastable defects is sensitively dependent on the confinement size, revealing that the metastable defects can be destabilized by optimizing the confinement size. Furthermore, the kinetic formation of the 4 × 4 square array of cylinders is verified by single-chain-in-mean-field (SCMF) dynamics simulations, which exhibits a considerable processing window with respect to the confinement size.