Phase separation in thin films of polymer blends: The influence of symmetric boundary conditions

Using nuclear reaction analysis composition-depth profiling, we investigate the influence of symmetric/asymmetric confining walls on the equilibrium c onfiguration of thin films of phase-separated polymer blends. Depth profile s of samples annealed under symmetric boundary conditions show a laterally averaged concentration, while samples confined by nonsymmetric walls show ( as in earlier studies) clear separation into two thin layers of coexisting phases. This suggests that for phase separation under symmetric boundary co nditions the interface between the two phases is orthogonal to the sample p lane, in line with recent theoretical discussion. (C) 2000 John Wiley & Son s, Inc.