LAMELLAR BLOCK-COPOLYMERS - DIFFUSION AND REDUCTION OF ENTANGLEMENT EFFECTS

Motion of symmetric diblock copolymer chains in the macroscopically or iented lamellar phase is studied by molecular-dynamics simulation. For diblocks of length N = 40 (1.1N(e)) and 100 (3N(e)), where N-e is the entanglement length of the homopolymer melt, the diffusion constant p arallel to the interface D-parallel to is nearly independent of chi, w hile the perpendicular component D-perpendicular to is strongly suppre ssed as chi, the Flory-Huggins parameter, is increased in agreement wi th theoretical predictions based on the Rouse model. For even longer c hains (N up to 400) a strong reduction of entanglement effects is obse rved. We argue that due to the reduced chain overlap in the lamellar p hase in this intermediate regime the chain motion is similar to an ell ipsoidal molecule in a smectic phase.