ORDERED STRUCTURES OF BLOCK COPOLYMER/HOMOPOLYMER MIXTURES .5. INTERPLAY OF MACROPHASE AND MICROPHASE TRANSITIONS

Self-assembly in the solution-cast films of binary mixtures of poly(styrene-block-isoprene) (SI) and homopolystyrene (HS) in the dry brush regime was studied by means of transmission electron microscopy (TEM) and light scattering (LS). This self-assembly involves the interplay of the macrophase and microphase transitions. In the case of a low volume fraction of SI, the macrophase separation between SI and HS first takes place via spinodal decomposition (SD) during the solvent evaporation process. This process is subsequently followed by the microphase transition, forming microdomains inside the macrodomains rich in SI. The process is eventually frozen by vitrification. The spatial concentration fluctuations developed by SD are visualized using the microdomains as a probe. In the case of the mixture with a cylinder-forming block copolymer, the following two structures were observed, depending on the solvent evaporation rate: a rapid evaporation develops the spherical microdomains of polyisoprene block chains, the centers of mass of which are dispersed in the continuous matrix of HS with the fractal-like spatial distribution; in the case of slow evaporation the self-assembled structure consists of lenslike macrodomains, in which cylindrical microdomains are packed hexagonally, dispersed in the continuous matrix of HS. The solution-cast film of the mixture with a lamella-forming block copolymer shows the oblate-spheroidal macrodomains, in which lamellar microdomains are packed like an onion, dispersed in a continuous matrix of HS.