Directing the Smectic Layer Orientation by Shear Flow in Hierarchical Lamellar‐within‐lamellar Liquid Crystalline Diblock Copolymers

Abstract

A self‐assembled lamellar‐within‐lamellar structure of a side chain liquid crystalline diblock copolymer was shear aligned to induce overall alignment and to direct the smectic layer orientation within the copolymer lamellae. The copolymer consisted of a polystyrene block and a poly(methyl methacrylate) block bearing cholesteryl mesogens with only short oxycarbonyloxyethyl spacers separating the mesogens from the backbone. Upon shearing, the copolymer lamellae exhibited uniaxial alignment whereas the smectic layers of the mesogens showed coexisting perpendicular and parallel orientations with respect to the copolymer lamellae. The fraction of the parallel oriented domains could be systematically increased by tuning the oscillation frequency and strain amplitude.magnified image

Hierarchical Structures in Lamellar Hydrogen Bonded LC Side Chain Diblock Copolymers

“…In the P4-50 and P4-75 samples the hydrogen bonding of CholHS is high enough to promote the perpendicular smectic subphase schematically depicted in Figure b. The same subphase structures can be found for example in the PS-P4VP(CholHS) samples with high CholHS content by Korhonen et al and in PMMA based diblock copolymers with covalent (every repeat unit carries a side chain) cholesterol side chains by Laiho et al without shear alignment . Thus, the binding of CholHS side chains to the host blocks plays a major role in the formation of the perpendicular smectic subphase.…”

“…The low attachment of CholHS leads to the side chains forming their own lamella inside the side chain block domain. The single layer packing is different from the smectic layers which are oriented parallel to block domain interfaces found in some side chain block copolymers after shear orientation or roll casting. , Instead, the single layer structure of Figure a seems not to be due to liquid crystalline type organization of the side chain blocks. Rather, it is a new type of self-assembly of side chain diblock copolymers resembling the microphase separation of linear triblock copolymers − or certain types of supramolecular tailed-dendron systems .…”

“…As stated earlier, usually the side chain blocks organize in smectic lamellae perpendicular to the block copolymer domain interfaces. Parallel alignment of the smectic layers can be achieved with external driving forces, such as roll casting , or shear alignment. , In the case of bent core mesogens hydrogen bonded to PS-P4VP, parallel smectic layers formed inside the P4VP domains after shearing . The authors argued that the parallel alignment was due to the low attachment ratio of the mesogens (one mesogen in every ten repeat units): the attached and nonattached parts of the P4VP chains would “microphase separate” into lamellar subphase inside the P4VP domains due to repulsion between the parts behaving like multiblock copolymers.…”

Electromagnetic shielding effectiveness of polycarbonate/graphene nanocomposite foams processed in 2-steps with supercritical carbon dioxide

“…The locations of these sets of peaks suggest the presence of bimodal orientation [8], which might be explained by the stretching of polymer chains and re-alignment of graphene platelets due to foaming [9] particularly if the cell growth or sample expansion is not isotropic, which is the case in the current study. TEM experiments showed different graphene platelet orientations between samples heated for 100 s (Figure 2f) and 40 s (Figure 2g), which supports that graphene platelets Figure 2.…”

Effects of metal loading and magnetic field strength on alignment of noncrystalline block copolymers doped with metal complexes

“…Control of the orientation of the block copolymers in such nanostructures is important for their applications in organic semiconductors [1][2][3], lithographic nanopatterning [4][5][6], separation membranes [7][8][9], and nanofabrication templates [10][11][12]. Many studies have focused on orienting block copolymers by applying stress [13][14][15][16], electric fields [17][18][19], and magnetic fields [20][21][22][23][24]. In the latter case, selfassembly of block copolymers that exhibit anisotropic magnetic susceptibility, such as liquid-crystalline block copolymers, is directed by application of a magnetic field; alignment of the block copolymers is achieved by means of orientation of the liquid-crystal mesogens.…”