Symmetric diblock copolymer thin films confined between homogeneous and patterned surfaces: Simulations and theory

We have investigated the ability of a simple phenomenological theory to des cribe the behavior of symmetric diblock copolymer thin films confined betwe en two hard surfaces. Prior knowledge of the morphology in the confined fil ms is crucial for applying this theory to predict the phase diagram of such systems. Taking advantage of our observations in Monte Carlo simulations, we use the theory to construct phase diagrams for thin films confined betwe en patterned-homogeneous surfaces, and obtain good agreement with our resul ts of simulations. Two conditions are essential for obtaining long-range or dered perpendicular lamellae: a lower stripe-patterned surface with the sur face pattern period L-s comparable to the bulk lamellar period L-0, and an upper neutral or weakly preferential surface. We have also examined the und ulation of perpendicular lamellae between two hard surfaces. For the cases of two homogeneous (preferential) surfaces and patterned-preferential surfa ces, our calculations using the phenomenological theory indicate that the a mplitudes of the undulation are on the same order of magnitude as observed in our Monte Carlo simulations, and are one order of magnitude larger than previously reported. The theory, however, is unable to capture the shape of the undulation. For the case of patterned-neutral surfaces, we find that a n earlier analysis is unable to yield the undulations that would stabilize the perpendicular lamellar morphology. We have addressed this issue and obt ained undulations that are consistent with our observations from Monte Carl o simulations. (C) 2000 American Institute of Physics. [S0021-9606(00)70322 -9].