Structural evolution of perpendicular lamellae in diblock copolymer thin films during solvent vapor treatment investigated by grazing-incidence small-angle X-ray scattering

The structural evolution in poly(styrene-b-butadiene) (P(S-b-B)) diblock copolymer thin films during solvent vapor treatment is investigated in situ using time-resolved grazing-incidence small-angle X-ray scattering (GISAXS). Using incident angles above and below the polymer critical angle, structural changes near the film surface and in the entire film are distinguished. The swelling of the film is one-dimensional along the normal of the substrate. During swelling, the initially perpendicular lamellae tilt within the film to be able to shrink. In contrast, at the film surface, the lamellae stay perpendicular, and eventually vanish at the expense of a thin PB wetting layer. During the subsequent drying, the perpendicular lamellae reappear at the surface, and finally, PS blocks protrude. By modeling, the time-dependent height of the protrusions can be quantitatively extracted. Discrimination of the bulk and surface behavior of diblock copolymer thin films featuring perpendicular lamellae during solvent vapor treatment is carried out by in situ, real-time grazing-incidence small-angle X-ray scattering. Within the film, the lamellae tilt in order to be able to shrink. During swelling, a thin surface layer of the polybutadiene block is formed, which during drying, retracts and results in polystyrene protrusions. The height of the protrusions is quantified.