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 t o obtain the true three-dimensional concentration profiles of polystyr ene (PS) and bromo-polystyrene (PBrx=0.79S where x = fraction of monom ers brominated) blend films as a function of PBrx=0.79S concentration. Upon annealing, it is found that the PBrS becomes encapsulated by the PS. The encapsulation provides for a continuous PS phase for all blen d compositions and explains the observed structures that are formed fo r different PBrS volume fractions. The encapsulation allows us to esti mate the dispersive contribution of the PBrS surface energy to be less than 20.6 dyn/cm.