  We investigate symmetric grain boundaries in a lamellar diblock copolymer
system. The form of the interface between two grains strongly depends on the
angle $\theta$, between the normals of the grains. When this angle is small,
the lamellae transform smoothly from one orientation to the other, creating the
chevron morphology. As $\theta$ increases, a gradual transition is observed to
an omega morphology characterized by a protrusion of the lamellae along the
interface between the two phases. We present a theoretical approach to find
these tilt boundaries in two-dimensional systems, based on a Ginzburg-Landau
expansion of the free energy. Calculated order parameter profiles and energies
agree well with transmission electron microscope experiments, and with full
numerical solution of the same problem.
