Parallel and Perpendicular Orientations Observed in Shear Aligned S_CA Liquid Crystal of Main-Chain Polyester

Abstract

Shear alignment behavior was examined for smectic CA (SCA) phase of main-chain BB-5(3-Me) polyester using a cone-and-plate fixture. In the smectic temperature region from 100 to 140 °C, two distinct orientations have been identified by wide-angle X-ray diffraction. At temperatures lower than 130 °C, the smectic layers arrange with unit normal perpendicular to the shear direction and parallel to the velocity gradient direction (so-called parallel orientation). Shearing at high temperatures near the isotropization temperature leads to the orientation of smectic layers with unit normal perpendicular to both the flow and velocity gradient directions (perpendicular orientation). At the intermediate temperatures, both orientations coexist. The SR-SAXS profile of the parallel oriented sample measured with irradiation along the vorticity direction includes a small peak with a spacing of around 80 Å in the velocity gradient direction that is parallel to the chain axis. The long spacing is roughly 5 times larger than the length of repeat unit, i.e., the smectic layer thickness (16.4 Å), showing the existence of chain-folded lamellae. The parallel orientation is attributed to mutual slide of the chain-folded lamellae. At higher smectic temperatures, on the other hand, the flow of the molecules within a smectic layer takes place preferentially to the mutual slide of lamellae, which is responsible for perpendicular orientation.

Thermotropic Liquid Crystals of Main‐Chain Polyesters having a Mesogenic 4,4′‐Biphenyldicarboxylate Unit, 14

“…Here, the molecules lie perpendicular to its axis. This unusual orientation is considered to result from the preferential alignment of chain folded lamellae [11][12][13][14][15][16] under a flow of drawing or shearing. In this work, we performed dynamic mechanical measurements on fibrous BB-5(3-Me) polyester specimens with these two distinct orientations.…”

Synthesis, Phase Behaviour and Mechanical Properties of Poly(2‐methyl‐1,3‐propanediol‐4,4′‐bibenzoate)

“…[18][19][20][21][22][23][24] The orientation of the macromolecular chains depends on the conditions of the test, and, in the case of drawing experiments, it has been observed that the orientation changes with temperature and strain rate. Thus, a normal, parallel orientation of the chains in relation to the stretching direction has been found for high strain rates and low temperatures, while a perpendicular orientation of the chains (anomalous orientation) is favoured at low strain rates and high temperature.…”

Structures and phase transformations of odd-numbered asymmetric main-chain liquid crystalline polyesters

“…A schematic unit cell model with two chains for the K M crystalline phase of BPE-C9 (b). methylene units are all in the trans-conformation [12][13][14][15][16][17][18]. Oddnumbered BPE-Cn polyesters have two possible bends: one is from the meta-linkage (configurational bend) at the end of the mesogenic groups, and the other is from the odd-number of methylene units in the spacers (conformational bend).…”

“…For example, a series of BB-n polyesters (n: the number of methylene units), synthesized via the melt condensation polymerization of p,p-bibenzoic acid (A-A type) and alkylene glycols (B-B type) monomers, demonstrated the structural odd-even effect. The even-numbered BB-n polyesters exhibited a low-ordered smectic A (SmA) phase, but the mesophase of the oddnumbered ones was identified to be an anticlinically tilted smectic C (SmC A ) phase layer-by-layer [12][13][14][15][16][17][18]. As an example of the morphological odd-even effect, a series of chiral polyesters were synthesized via the solution condensation polymerization of non-racemic chiral A-B type monomers, (R This is a morphological odd-even effect: the PET(R*)-n polyesters containing the identical R* chiral center but having nZodd developed righthanded helical crystals while nZeven grew left-handed helical crystals [19][20][21][22][23][24][25][26][27].…”