Creation of lateral structures in diblock copolymer thin films during vapor uptake and subsequent drying - Effect of film thickness

We have studied the structure formation in compositionally nearly symmetric poly(4-octylstyrene-b-butylmethacrylate) diblock copolymer films during exposure to saturated vapor of n-hexane (a poor solvent for both blocks) and subsequent drying using real-time, in situ grazing-incidence small-angle X-ray scattering (GISAXS). Previous bulk studies revealed a lamellar structure after thermo-annealing; and surface studies on hexane treated samples revealed a lateral surface structure (Černoch et al., 2007) [14]. We focus here on the effect of film thickness which is varied between 1.3 and 2.0 times the bulk lamellar thickness. We report on the lateral repeat distance as well as on the correlation length in the film plane. Complex, non-monotonous behavior is observed for both parameters. Upon drying, the lateral structure created during vapor treatment is stable only for the thick film, not for the intermediate and the thin film. The kinetics depends strongly on the film thickness; especially for the thinnest film, it is very slow. For all film thicknesses, we attempt to identify the most stable morphology, occurring when the inner film structure is close to the one in the bulk.