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 we re studied by small-angle X-ray scattering (SAXS) and transmission ele ctron microscopy (TEM) in order to determine the microphase structure. The cylindrical microstructure is confirmed for both copolymers, wher eas, in the mixture, both techniques have unambiguously shown that a r egular lamellar structure is obtained at the polymer-polymer compositi on P1:P2 = 1:1 (ratio of the numbers of chains). Qualitatively, the sa me results are obtained for corresponding systems simulated by the coo perative 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 structu res in the blend of composition P1:P2 = 1:1, in contrast to the microf ibrillar morphology of the copolymers. The simulation additionally ind icated a polymer-polymer microseparation. The experimental and simulat ion results are compared with theoretical predictions based on the sel f consistent field theory.