Pattern formation mechanisms in sphere-forming diblock copolymer thin films

Abstract

The order–disorder transition of a sphere-forming block copolymer thin film was numerically stud-ied through a Cahn–Hilliard model. Simulations show that the fundamental mechanisms of patternformation are spinodal decomposition and nucleation and growth. The range of validity of each re-laxation process is controlled by the spinodal and order–disorder temperatures. The initial stagesof spinodal decomposition are well approximated by a linear analysis of the evolution equation ofthe system. In the metastable region, the critical size for nucleation diverges upon approaching theorder–disorder transition, and reduces to the size of a single domain as the spinodal is approached.Grain boundaries and topological defects inhibit the formation of superheated phases above the order–disorder temperature. The numerical results are in good qualitative agreement with experimental dataon sphere-forming diblock copolymer thin films.