  To enlighten the nature of the order-disorder and order-order transitions in
block copolymer melts confined in narrow capillaries we analyze peculiarities
of the conventional Landau weak crystallization theory of systems confined to
cylindrical geometry. This phenomenological approach provides a quantitative
classification of the cylindrical ordered morphologies by expansion of the
order parameter spatial distribution into the eigenfunctions of the Laplace
operator. The symmetry of the resulting ordered morphologies is shown to
strongly depend both on the boundary conditions (wall preference) and the ratio
of the cylinder radius and the wave length of the critical order parameter
fluctuations, which determine the bulk ordering of the system under
consideration. In particular, occurrence of the helical morphologies is a
rather general consequence of the imposed cylindrical symmetry for narrow
enough capillaries. We discuss also the ODT and OOT involving some other
simplest morphologies. The presented results are relevant also to other
ordering systems as charge-density waves appearing under addition of an ionic
solute to a solvent in its critical region, weakly charged polyelectrolyte
solutions in poor solvent, microemulsions etc.
