The ability of random copolymer brushes and cross-linked mats to induce the vertical orientation of domains in overlying films of lamellae-and cylinder-forming block copolymers was investigated as a function of the composition. The substrate-modifying layers consisted of styrene and methyl methacrylate random copolymers and contained either a terminal hydroxyl group or a third polar comonomer of 2-hydroxyethyl methacrylate (HEMA) for grafting brushes to silicon oxide surfaces or glycidyl methacrylate (GMA) for crosslinking the random copolymer into a mat. Polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) lamellaeand cylinder-forming block copolymers (both PS and PMMA minority block copolymers) were deposited and annealed on the modified surfaces. In all cases the vertical orientation of domains was observed for a range of random copolymer composition, but the ranges of composition were different for each combination of surface layer and block copolymer. The cylindrical domains of PS exhibited vertical structures for a very narrow range of compositions compared to cylindrical domains of PMMA or lamellae. As expected, the incorporation of polar HEMA or GMA monomers in the surface layers shifted the composition range for the perpendicular orientation of domains to higher fractions of styrene. The results are discussed in terms of the equilibration of the films in the presence of the chemically modified surfaces.

We report the induction of perpendicularly oriented cylindrical domains in PS-b-PMMA block copolymer (BCP) films thicker than 100 nm by thermally annealing on a substrate modified with a random copolymer. The effects of annealing temperature, composition of the substrate-modifying random copolymer, and BCP film thickness on the morphology of PMMA cylinder forming PS-b-PMMA were studied. For BCP films thicker than 100 nm, the fabrication of perpendicular PMMA cylinders is highly dependent on both the substrate-modifying random copolymer and the annealing temperature as these two parameters control the interactions of the BCP with the substrate and the free surface, respectively. We found the best perpendicular structures to be created by using a random copolymer brush with a styrene fraction (F St) near 0.70 and an annealing temperature near 230 °C. Perpendicular cylinder structures were achieved in ∼300 nm thick films using these conditions. When the BCP film was thicker than 300 nm, nucleation and growth of the microdomains proceeded independently from each interface. We present scanning electron microscope (SEM) and cross-sectional transmission electron microscope (TEM) images of these perpendicular structures and explain the results on the basis of previous simulation reports.

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The phase behavior and dimensional scaling of symmetric ternary blends composed of poly(styrene-block-methyl methacrylate) block copolymers and the corresponding polystyrene and poly(methyl methacrylate) homopolymers in thin films were investigated as a function of χN (the product of the Flory−Huggins interaction parameter and the overall degree of polymerization of the block copolymer), α (the ratio of the degree of polymerization of the homopolymers to that of the block copolymer), and ϕH (the volume fraction of homopolymers in the blends). The phase transitions were characterized by three methods: disappearance of high-order peaks in the fast Fourier transform (FFT) spectra from scanning electron microscopy (SEM) images, application of the amphiphilicity factor determined from the FFTs, and, in the case of thicker films, the appearance of either microphase- or macrophase-separated domains in SEM images. Above the order−disorder transition (ODT) in the χN−ϕH phase diagram, the symmetric ternary blends transitioned from lamellae to a microemulsion and then to macrophase-separated domains as ϕH increased. The phase transitions depended weakly on χN and α in the range of 12.7 ≤ χN ≤ 36.7 and 0.20 ≤ α ≤ 0.99. The periods of swollen lamellae and microemulsions (L B) were determined as a function of ϕH and α and were well described empirically with L B = L 0/(1 − ϕH)β, where L 0 is the natural period of pure block copolymer and β is a parameter that depends linearly on α with values ranging from ∼0.5 to 1.5.