Curvature as a guiding field for textured Block Copolymer Thin Films and Membranes

Orateur : Daniel A. VEGA (Instituto de Física del Sur, Universidad Nacional del Sur - CONICET, Argentina)

Ordered phases lying on curved backgrounds are not only commonly found in nature in systems like viral capsids, pollen grains or the silica skeletons of unicellular algaes but they can be also obtained in different experimental systems, like self-assembling colloidal particles, block copolymers or liquid crystals [1-3]. In these curved systems, it was found that non-Euclidean geometry could stabilize exotic defects to alleviate the stress imposed by the curvature and to reduce geometric frustration [2]. Here we employed a Brazovskii free energy model and self-consistent field theory (SCFT) calculations to analyze the coupling between the smectic textures developed by cylinder forming block copolymer systems and the curvature of the film [4,5]. For weak curvatures, it was found that the free energy of the block copolymer film follows a Helfrich form, with a bending constant that depends on the pattern orientation with regard to the directions of main curvature. The strong anisotropy in the bending constant explains the main geometrical features of the out-of-plane deformations observed in free-standing block copolymer membranes, where disclinations act as sources of Gaussian curvature [6]. These results are in very good agreement with experimental data of poly(styrene)-co-poly(ethylene-alt-propylene) free-standing membranes and thin films deposited onto curved substrates.

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