Morphology transitions of AB diblock copolymer melts confined in nanocylindrical tubes.

By employing Monte Carlo simulations for various values for the interactions energies epsilonAB between the beads A and B, the selectivity of the surface for one of the beads, and the diameter d of the nanotube, the morphology transitions in A5B5 and A7B3 diblock copolymer melts were investigated. In symmetrical systems and for a negligible preference of the surface for A and B and not too large values of d, as epsilonAB increases, increasingly thicker stacked-disk macrodomains normal to the tube surface were formed. When epsilonAB became sufficiently large, a configuration transition to helixes occurred which became deformed at larger values of epsilonAB. The helixes contained an imperfect single helix of A coupled with an imperfect single helix of B or imperfect double helixes of A coupled with imperfect double helixes of B. When at constant and relatively large epsilonAB, the attractive interaction epsilonAS between the A bead and the surface was increased, a transition from a succession consisting of stacked disks and a helix to a helical one occurred, which changed to a circular lamellar structure at a sufficiently large attraction epsilonAS by the surface. When the diameter d was increased, in addition to the helixes already mentioned imperfect triple helixes of A coupled with triple helixes of B were identified. In the asymmetrical case, two kinds of helixes were observed, namely, those identified in the symmetrical case, as well as a helix formed by one kind of beads immersed in the matrix of the other one.