Influence of blend composition on phase separation and dewetting of thin polymer blend films

Thin polymer blend films of deuterated polystyrene (dPS) and poly(p-methyls tyrene) (PpMS) with several blend compositions between 95:5 and 5:95 were p repared on top of glass substrates. The samples were examined right after p reparation and after annealing. Their surface morphology was investigated w ith scanning force microscopy (SFM). A statistical analysis of the SFM data yielded the rms roughness as well as the most prominent in-plane length pa rallel to the sample surface. Information about the density profile perpend icular to the sample surface is gained from neutron reflectivity measuremen ts in the region of total external reflection. Right after preparation dPS segregates to the air interface, while during annealing at a temperature ab ove the glass transition temperature of both polymers, PpMS builds up a top layer toward the interfaces. Depending on blend composition and annealing time, different surface topographies are evolving. The examined film thickn esses are below a critical thickness, ensuring that composition fluctuation s directed normal to the surface are suppressed. However, the small film th ickness constrains kinetics largely to two dimensions. The surface morpholo gy is controlled by an interplay between phase separation and dewetting.