Transition to Lamellar-Catenoid Structure in Block-Copolymer Melts

The microphase transition in symmetric and nearly symmetric diblock-copolymer melts is studied expanding the density of the periodic structures in multiple harmonics. We analyze the periodicity in the weak segregation regime minimizing the Landau mean field free energy of the structure. The density distribution inside the unit cell is constructed for various morphologies. A three-dimensional hexagonal structure, identified as a “lamellar-catenoid”, is found to be the equilibrium structure at the transition. It consists of alternating lamellar domains connected by an orthogonal array of hexagonally packed cylinders.