LAMELLAR STRUCTURE FORMATION IN THE MIXTURE OF 2 CYLINDER-FORMING BLOCK-COPOLYMERS

Two cylinder-forming polystyrene-block-polybutadiene block copolymers of type A-B with antisymmetric composition (polymer P1 with A:B = 3:1 (w/w) and polymer P2 with A:B = 1:3 (w/w)) and their binary mixture were studied by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) in order to determine the microphase structure. The cylindrical microstructure is confirmed for both copolymers, whereas, in the mixture, both techniques have unambiguously shown that a regular lamellar structure is obtained at the polymer-polymer composition P1:P2 = 1:1 (ratio of the numbers of chains). Qualitatively, the same results are obtained for corresponding systems simulated by the cooperative motion algorithm (CMA). Direct observations of the structure as well as the cooperative structure factors determined in the strong segregation limit for the simulated systems indicated lamellar structures in the blend of composition P1:P2 = 1:1, in contrast to the microfibrillar morphology of the copolymers. The simulation additionally indicated a polymer-polymer microseparation. The experimental and simulation results are compared with theoretical predictions based on the self consistent field theory.