Organization of layer-type supramolecular nanostructures of a combined liquid-crystalline homopolymer toward lattice packing

For a designed LC homopolymer, bearing a polyimide backbone mesogen and two terminally-connected cyanobiphenyl mesogens via aliphatic spacers in a repeat unit, the formation of layer-type supramolecular nanostructures, and involved organization route within sheared film have been studied in this research. The anisotropic layer scheme induced within sheared film identified the feasible phase separation between distinct mesogens under the restriction of connection spacers. Further considering the periodic correlation of 2.3 nm preferably along the stacking direction, alternate stacks of mesogen bilayers were accounted for the growth of nanostructures. The shear-aligned assembly of layer-type nanostructures led to the presence of orientational order along the film x- and z-axes, and thus the formation of biaxial supramolecular nematic phase. The further annealing process at 160 °C initiated the development of orthorhombic lattice packing, which is conceivably via parallel sliding motion of nanostructures. This growth mechanism explains the existence of large range of bond orientation order, but less extensive positional order. For this orthorhombic lattice, the preferred azimuthal orientation and unusually high aspect ratio between transverse lattice dimensions approved the development of lattice packing from prior stacking of layer-type nanostructures. Upon annealing at 240 °C, the continue ordering process favored closer interaction between neighboring backbone mesogens along the b-axis, which nevertheless expanded the a-axis dimension and caused the packing of cyanobiphenyl mesogens much less oriented. These evolved structural features were attributed to the presence of a regular buckled pattern of cyanobiphenyl bilayers within lattices, as a result of mechanical deformation while being unable to linearly extend within insufficient lattice dimension. These structural analyses helps to describe multiple-step organization of layer-type nanostructures toward lattice packing, which is not likely referred to the packing behavior of individual repeat units.