  We present several ordering mechanisms in diblock copolymers. For
temperatures above the order-disorder temperature and in the weak segregation
regime, a linear response theory is presented which gives the polymer density
in the vicinity of confining flat surfaces. The surfaces are chemically
patterned where different regions attract different parts of the copolymer
chain. The surface pattern or template is decomposed into its Fourier modes,
and the decay of these modes is analyzed. The persistence of the surface
pattern into the disordered bulk is given for several types of patterns (e.g.
uniform and striped surface). It further is shown that complex morphology can
be induced in a thin film even though the bulk is disordered. We next consider
lamellar diblock copolymers (low temperature regime) in the presence of a
striped surface. It is shown that lamellae will appear tilted with respect to
the surface, if the surface periodicity is larger than the bulk one. The
lamellae close to the surface are strongly distorted from their perfect shape.
When the surface and lamellar periodicities are equal lamellae form
perpendicular to the surface. Lastly, the transition from parallel to
perpendicular lamellae to the surfaces in a thin film is presented. The
transition between the two states depends on the surface separation and
strength of surface interactions. We further calculate the phase diagram in the
presence of perpendicular electric field favoring perpendicular ordering. In
the strong segregation limit we introduce a simple model to calculate the phase
diagram of the fully parallel, fully perpendicular and mixed (parallel and
perpendicular) states.
