| Abstract
| - Hierarchical ordering in a series of side-group liquid-crystal block copolymers wasinvestigated in the bulk via differential scanning calorimetry (DSC), polarized light microscopy, small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS). The diblock copolymerscomprise a polystyrene block and a block of poly(methyl methacrylate) bearing a chiral biphenyl estermesogenic unit linked to the backbone by a dodecyloxy spacer. A series of copolymers with different volumefractions of mesogenic block were prepared by atom transfer radical polymerization. Ordering of mesogensinto a smectic phase is characterized by a period 3.5 nm. Glass transition temperatures and the clearingtemperature for each sample were determined by DSC. Additional ordering occurs due to microphaseseparation of the block copolymer at a length scale of 22−27 nm, as confirmed by SAXS and SANS. Theorder−disorder transition was found to be coincident with the smectic−isotropic transition for a samplecomprising PS cylinders. A hexagonal morphology was determined for samples with both a minority anda majority liquid-crystal block. Remarkably, the morphology comprising liquid-crystal (LC) cylinders ina polystyrene matrix could be oriented by slow cooling through the clearing temperature, in the presenceof a strong magnetic field. The inverse morphology of cylinders formed by the PS block in an LC matrixwas not oriented in this way. This is ascribed to the nucleation of defects around the nanorods in the LCmatrix. The thin film nanostructure was investigated by atomic force microscopy (AFM) and X-rayreflectivity for a sample comprising PS cylinders. AFM confirmed a hexagonal-packed cylinder morphologyin thin films with coexisting parallel and perpendicular orientations of rods with respect to the substrate.The presence of Bragg peaks in specular X-ray reflectivity intensity profiles indicates a proportion ofsmectic layers lying parallel to the substrate, with a spacing similar to that in bulk. Our results providea comprehensive picture of hierarchical ordering in the bulk and in thin films.
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