Ellipsoidal structures have attracted significant interest because of their anisotropic properties. For instance, in photonic crystals, both positional and orientational order of the ellipsoids are required. In this presentation, we present a versatile, facile, and efficient strategy to fabricate crystals of soft domains in block copolymers with orientational and positional order via a step-shear deformation. Starting from a thermodynamically stable mesophase of copolymers (e.g., spherical domains/equilibrium BCC mesophase) a step-shear deformation provides an instantaneous, anisotropic stimulus that deforms the copolymer domains and simultaneously stretches the macromolecular conformations. At fixed deformation, the molecular stress subsequently relaxes to an equilibrium where the shape and orientation of the obtained domains are dictated by the packing of the deformed domains. Since the residual molecular stress is minuscule, the relaxation of the morphology via slippage of planes of domains in the absence of external stress is extremely slow i.e., the crystal of soft domains with positional and orientational order is pseudometastable. Our strategy also allows for low volume fractions of domains (compared to colloidal systems). Both, Single-Chain-in-Mean-Field (SCMF) simulations and self-consistent field theory (SCFT) calculations, are employed to demonstrate the pseudometastability of the obtained domains. Varying the magnitude of the step-shear strain and the composition of the block copolymer, we can independently control the asphericity and orientation of the domains. Our study provides a new concept for fabricating soft, positionally and orientationally ordered crystals with potential applications in engineering functional materials. Extensions to other than spherical mesostructures are additionally discussed.

Fabrication of ellipsoidal mesostructures in block copolymers via a step-shear deformation

256th National Meeting (2018)

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