Self-Assembly of ABC Star Triblock Copolymer Thin Films Confined with a Preferential Surface: A Self-Consistent Mean Field Theory

Abstract

The microphase separation and morphology of a nearly symmetric A(0.3)B(0.3)C(0.4) star triblock copolymer thin film confined between two parallel, homogeneous hard walls have been investigated by self-consistent mean field theory (SCMFT) with a pseudospectral method. Our simulation experiments reveal that under surface confinement, in addition to the typically parallel, perpendicular, and tilted cylinders, other phases such as lamellae, perforated lamellae, and complex hybrid phases have been found to be stable, which is attributed to block-substrate interactions, especially for those hybrid phases in which A and B blocks disperse as spheres and alternately arrange as cubic CsCl structures, with a network preferred structure of C block. The results show that these hybrid phases are also stable within a broad hybrid region (H region) under a suitable film thickness and a broad field strength of substrates because their free energies are too similar to being distinguished. Phase diagrams have been evaluated by purposefully and systematically varying the film thickness and field strength for three different cases of Flory-Huggins interaction parameters between species in the star polymer. We also compare the phase diagrams for weak and strong preferential substrates, each with a couple of opposite quality, and discuss the influence of confinement, substrate preference, and the nature of the star polymer on the stability of relatively thinner and thick film phases in this work.