the degree of polymerization.

In the strong segregation limit the free energies of all microphases scale the same way with chain length and interfacial tension, so the phase boundaries become independent of the strength of the repulsion $\chi$ between A and B monomers and depend only on the composition $f$. Semenov’s calculation in effect gave a lower bound to the free energy of the L, C, and S phases because the phases he constructed did not fill space, but were micelles of the corresponding topology [@olmsted94a]. This approximation treats the $A\!-\!B$ interface and outer block surface as having the same circular or spherical shape, and is sufficient for understanding the qualitative aspects of the transitions between the phases.

Experiments followed the theories of Leibler and Semenov and quickly discovered a new phase,[@thomas86; @hasegawa87; @anderson88], originally thought to be ordered bicontinuous double diamond (here denoted D), of $Pn\bar{3}m$ symmetry, but recently shown to be of $Ia\bar{3}d$ symmetry [@Hajd+94; @Fors+94; @Schu+96] and related to the minimal surface known as the gyroid (G).[@schoen70] The G phase occurs for compositions between those of the L and C phases, can occur directly from the disordered phase upon increasing the incompatibility $\chi N$, and is found 