Alignment of Self-Assembled Hierarchical Microstructure in Liquid Crystalline Diblock Copolymers Using High Magnetic Fields

Abstract

Large area microdomain alignment in a ferroelectric liquid crystalline diblock copolymer (LCBCP) poly(styrene)-block-poly(isoprene-LC), (PS-PILC), incorporating a biphenyl 3-nitro-4-alkoxy- benzoate LC mesogenic group and a non-LC block hexagonally packed cylinder microstructure, was successfully accomplished by application of a magnetic field at elevated temperatures. Small- and medium- angle X-ray scattering demonstrated that the PS cylinders in the LC matrix orient over large areas with their long axes perpendicular to the applied magnetic field. Correspondingly, the smectic layers of the LC mesophase in the matrix are also perpendicular to the field as the anchoring of the mesogens at the intermaterial dividing surface (IMDS) between the cylindrical microdomains and the matrix is planar (homogeneous) in this material. A negative diamagnetic anisotropy for the LC mesogens is inferred from the data. A lamellar sample was also studied and found to exhibit no preferred microstructural orientation when subjected to the magnetic field. This result is consistent with the orientational state degeneracy of planar anchoring of mesogens at the flat lamellar IMDS and closely parallels our prior results obtained by orientation of nonferroelectric LCBCPs using oscillatory shear.