  We have studied structure formation in a confined block copolymer melt by
means of dynamic density functional theory (DDFT). The confinement is
two-dimensional, and the confined geometry is that of a cylindrical nanopore.
Although the results of this study are general, our coarse-grained molecular
model is inspired by an experimental lamellae-forming PS-PBD diblock copolymer
system (Shin et al, Science, 306, 76 (2004)), in which an exotic toroidal
structure was observed upon confinement in alumina nanopores. Our computational
study shows that a zoo of exotic structures can be formed, although the
majority, including the catenoid, helix and double helix that were also found
in Monte Carlo (MC) nanopore studies, are metastable states. We introduce a
general classification scheme and consider the role of kinetics and
elongational pressure on stability and formation pathway of both equilibrium
and metastable structures in detail. We find that helicity and three-fold
connections mediate structural transitions on a larger scale. Moreover, by
matching the remaining parameter in our mesoscopic method, the Flory-Huggins
parameter, to the experimental system, we obtain a structure that resembles the
experimental toroidal structure in great detail. Here, the most important
factor seems to be the roughness of the pore, i.e. small variations of the pore
radius on a scale that is larger than the characteristic size in the system.
