The self-assembly of poly(ferrocenyldimethylsilane-b-methyl methacrylate) block copolymers, with PFDMS contents of 9−61 wt % (block ratios 1:23−1:1.5), is described. PFDMS-b-PMMA block copolymers form remarkable cylindrical micelles with very narrow diameter distributions at block ratios in the range of 1:10−1:6 (18−26 wt % PFDMS) in the block-selective solvent acetone, which is a good solvent for PMMA and a nonsolvent for PFDMS. The micelles, with a PFDMS core and a PMMA corona, were studied in solution by means of dynamic light scattering, 1H NMR spectroscopy, and cryo-transmission electron microscopy. Micelles were also deposited on silicon substrates by dip-coating and characterized with atomic force microscopy and scanning electron microscopy. The micelles were over 3 μm long and had an overall diameter of around 22 nm. Dynamic light scattering experiments confirmed the formation of rodlike micellar aggregates in acetone. The cylindrical micelles exhibited a rod-to-sphere transition around 60 °C. When cooled below this transition temperature, the micelles reassembled back to their original aggregation state. Depolarized DLS experiments showed no rotational contribution to the measured decays of the autocorrelation functions. We ascribe this to the extreme length of the micelles, which arrests rotational movement. 1H NMR spectra recorded in acetone-d 6 showed PFDMS signals, indicating that these blocks in the micellar cores have some mobility. This suggests that the cores are not in a crystalline state and that crystallization is not a driving force in the formation of these PFDMS-b-PMMA cylindrical micelles, but rather the contrast in solvophilicity between the blocks, which in the bulk are in the strong segregation limit.

Articles you may be interested inBlock copolymer self assembly for design and vapor-phase synthesis of nanostructured antireflective surfaces J. Vac. Sci. Technol. B 32, 06FE02 (2014); 10.1116/1.4896335Directed self-assembly of ternary blends of block copolymer and homopolymers on chemical patterns J. Vac. Sci. Technol. B 31, 06F301 (2013); 10.1116/1.4818882 Curing process of silsesquioxane in self-organized diblock copolymer template Block copolymers can self-assemble to generate patterns with nanoscale periodicity, which may be useful in lithographic applications. Block copolymers in which one block is organic and the other contains Si are appealing for self-assembled lithography because of the high etch contrast between the blocks, the high etch resistance of the Si-containing block, and the high Flory-Huggins interaction parameter, which is expected to minimize line edge roughness. The locations and long range order of the microdomains can be controlled using shallow topographical features. Pattern generation from poly͑styrene͒-poly͑ferrocenyldimethylsilane͒ and poly͑styrene͒-poly͑dimethyl-siloxane͒ block copolymers, and the subsequent pattern transfer into metal, oxide, and polymer films, is described.

No abstract