Effect of Film Thickness on the Phase Behaviors of Diblock Copolymer Thin Film

A phase diagram was constructed for a polystyrene-block-polyisoprene (PS-b-PI, MW = 32 700, fPI = 0.670) in thin films on Si wafer as a function of film thickness over the range of 150−2410 nm (7−107L0 (L0: domain spacing)). The PS-b-PI exhibits a variety of ordered phases from hexagonally perforated lamellar (HPL) via double gyroid (DG) to hexagonally packed cylinder (HEX) before going to the disordered (DIS) phase upon heating. The morphology of the PS-b-PI in thin film was investigated by grazing incidence small-angle X-ray scattering, transmission electron microscopy, and transmission electron microtomography. In thin film, the phase transition temperature is difficult to be determined unequivocally with in situ heating processes since the phase transition is slow and two phases coexist over a wide temperature range. Therefore, in an effort to find an “equilibrium” phase, we determined the long-term stable phase formed after cooling the film from the DIS phase to a target temperature and annealing for...