Effect of confinement on the ordering of symmetric diblock copolymers: application of interfacial statistical associating fluid theory

Diblock copolymers consist of two chemically distinct polymer chains (blocks) covalently bonded together. Due to the differences in the physiochemical properties of these blocks, the copolymers can undergo order-disorder transitions (ODT) at the molecular level, resulting in microphase-separated states. Control of these microstructures has significant impact on the technological applications of diblock copolymers. Diblock copolymers exhibit a variety of microstructures, which depend on the relative compositions of the two distinct blocks. In the case of symmetric diblock copolymers, the equilibrium structure is the lamellar structure where each lamellar layer is an A-B or B-A repeat unit. We use interfacial statistical associating fluid theory (iSAFT) density functional theory to analyse the morphologies of symmetric diblock copolymers in bulk melts and ultra-thin films confined between two planar surfaces. For bulk melts, the effect of the length of the copolymer and incompatibility between the blocks of the copolymer on the lamellar structure is discussed. For copolymer thin films, the effect of the surface interactions and the film thickness on the microstructure is investigated.