Edge dislocations in copolymer lamellar films

Thin films of symmetric diblock copolymers on a flat solid surface form lamellae parallel to the substrate. The uppermost layer of the film may be incomplete and made of domains with a thickness equal to the lamellar period L. We investigate these domains both theoretically and experimentally. The domain edge is associated with a dislocation in the lamellar order which has been observed by transmission electron microscopy. We extend the linear elasticity theory of smectic liquid crystals, to include the effect of the surface tension at the air-polymer interface. We calculate the surface profile above a domain edge and the position (depth) of the dislocation. This profile is studied by atomic force microscopy for polystyrenepolybutylmethacrylate films. The comparison between theoretical and experimental profiles allows an estimation of the smectic elastic constants and of the internal surface tension between the two blocks of the copolymer.