Phase Separation of Polystyrene and Bromo−Polystyrene Mixtures in Equilibrium Structures in Thin Films

Scanning transmission X-ray microscopy (STXM), atomic force microscopy (AFM), and dynamic secondary ion mass spectrometry (DSIMS) were used to obtain the true three-dimensional concentration profiles of polystyrene (PS) and bromo−polystyrene (PBr x = 0 .79 S where x = fraction of monomers brominated) blend films as a function of PBr x = 0 .79 S concentration. Upon annealing, it is found that the PBrS becomes encapsulated by the PS. The encapsulation provides for a continuous PS phase for all blend compositions and explains the observed structures that are formed for different PBrS volume fractions. The encapsulation allows us to estimate the dispersive contribution of the PBrS surface energy to be less than 20.6 dyn/cm.