EQUILIBRIUM SURFACE ORIENTATION OF LAMELLAE

We theoretically investigate the equilibrium orientation of lamellae a rising from symmetric diblock copolymers in the presence of a hard wal l. Firstly, the wall may preferentially wet with one of the species of the copolymer, thus favoring lamellar planes parallel to the wall. Se condly, chains are more easily stretched along the wall than they are in bulk; this favors the lamellar planes being perpendicular to the wa ll. Finally, the enhanced chain end density near the wall in the paral lel orientation favors the planes flat along the wall. As molecular we ight M approaches infinity, the most important effect is the wetting a pproximately M0, followed by the nematic effect approximately M-2/3, a nd lastly followed by the end effect approximately M-8/9. In experimen tally available copolymer domains, we find that the nematic and end ef fects have comparable magnitude. This magnitude appears more than adeq uate to influence the orientation of the lamellae. Lastly, we discuss effects of substrate roughness.