  We study a model of flexible block copolymers (BCPs) in which there is an
enlthalpic preference for local alignment, among like-block segments. We
describe a generalization of the self-consistent field theory (SCFT) of
flexible BCPs to include inter-segment orientational interactions via a
Landau-DeGennes free energy associated with a polar or nematic order parameter
for segments of one component of a diblock copolymer. We study the equilibrium
states of this model numerically, using a pseudo-spectral approach to solve for
chain conformation statistics in the presence of a self-consistent torque
generated by inter-segment alignment forces. Applying this theory to the
structure of lamellar domains composed of symmetric diblocks possessing a
single block of "self-aligning", polar segments, we show the emergence of
spatially complex segment order parameters (segment director fields) within a
given lamellar domain. Because BCP phase separation gives rise to spatially
inhomogeneous orientation order of segments even in the absence of explicit
intra-segment aligning forces, the director fields of BCPs, as well as
thermodynamics of lamellar domain formation, exhibit a highly non-linear
dependence on both the inter-block segregation ($\chi N$) and the enthalpy of
alignment ($\varepsilon$). Specifically, we predict the stability of new phases
of lamellar order in which distinct regions of alignment coexist within a
single mesodomain, and which spontaneously break the symmetry of the lamella
pattern of composition in the melt via in-plane tilt of the director in the
centers of the like-composition domains. We show further that, in analogy to a
Freedericksz transition in confined nematics, that the elastic costs to
reorient segments within the domain, as described by Frank elasticity, increase
the threshold value $\varepsilon$ needed to induce this intra-domain phase
transition.
