Ordering of a lamella-forming fluid near an interface.

By using wedged thin films, we have measured the effect of interfaces on the ordering of an anisotropic fluid in real space. Symmetric diblock copolymers can form an ordered lamellar fluid, and the preference of the substrate for one of the blocks can induce order well into the disordered bulk phase. The induced order decays away from the substrate with a length scale that diverges at the bulk ordering transition. Ordering and disordering kinetics are found to differ: all layers relax identically upon disordering, whereas the formation of lamellae is found to vary with the distance from the substrate and can be understood from the time-dependent Ginzburg-Landau theory.