Shapes and shape transformations of two-component membranes of complex topology

The properties of two-component membranes, which form doubly periodic surfaces of complex topology, are studied in the strong-segregation limit. The membrane is described within the framework of curvature elasticity; the two components are distinguished by their spontaneous curvatures in this case. Four different domain morphologies are considered for a square lattice of passages: rings of component alpha inside the passage and caplets of component alpha outside the passage, as well as rings and caplets of component beta. The dependences of the shape of the membrane and of the shape of the domain boundary are calculated as a function of composition. On the basis of a calculation of the curvature energy we conjecture the existence of doubly periodic, piecewise constant-mean-curvature surfaces. For small and intermediate line tensions, we predict several phase transitions between the investigated morphologies. We also discuss briefly the existence and shapes of vesicles of piecewise constant mean curvature.