  We study the effect of monomer immobilization (quenching) on the orientation
of the lamellae in symmetric diblock copolymer thin films with neutrally
wetting surfaces. A small fraction of the monomers immediately next to the
solid substrate is presumed to be quenched. In both the weak segregation limit
and the strong segregation limit, quenching favors the lamellae orienting
perpendicular to the film. Quenching inhibits the order-disorder transition
twice as much for the parallel orientation as for the perpendicular.
