The Morphology of Liquid-Crystalline Polymers and the Possible Consequences for their Rheological Behaviour

Chapoy, L. L.; Marcher, Bj⊘rn; Rasmussen, Knud

doi:10.1080/02678298808086625

Cited by 18 publications

(4 citation statements)

References 49 publications

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“…In a number of cases the optical scattering texture of t l c p s in the molten state is dominant and the length scale of the scattering entities is close to the resolution of the optical microscope. This texture has been called a tight texture (Viney et al 19836), a dense defect texture (Alderman & Mackley 1985), or a polydomain (Chapoy et al 1988).…”

Section: Introductionmentioning

confidence: 99%

The effect of shear on thermotropic liquid crystalline polymers

Gervat

Mackley

Nicholson

et al. 1995

Phil. Trans. R. Soc. Lond. A

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We present and review optical and rheological data on a number of sheared thermotropic liquid crystal polymers LCPs. Optical observations were carried out by using a shearing apparatus that was designed for these and additional in situ X-ray measurements. X-ray data on sheared LCPs are also presented together with orientation relaxation measurements made on the cessation of flow. To reconcile the optical, X-ray and rheological data, a numerical scheme is constructed that can qualitatively, and in some cases quantitatively predict observed behaviour. Essential elements of the model are concerned with a local molecular anisotropy, a molecular correlation coefficient, and a local defect structure. The model shows, among other predictions, that stress relaxation is essentially decoupled from both orientation and optical relaxation. In addition the presence of a defect texture influences orientation aspects more than the rheology.

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Section: Introductionmentioning

confidence: 99%

The effect of shear on thermotropic liquid crystalline polymers

Gervat

Mackley

Nicholson

et al. 1995

Phil. Trans. R. Soc. Lond. A

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“…Initially (i.e., t = 0) the melt-spun fiber shows no domain structure. However, the micrograph taken at t = 10 min shows a banded structure perpendicular to the fiber axis, and the banded structure persisted as the isothermal annealing continued for 24 h. It should be remembered from the DSC thermograms given in Figure 2 that, when annealed at 130 °C for a period of up to 24 h, meltspun fibers exhibited two endothermic peaks, one at ~120 °C representing the melting point (Tm2) of lowtemperature melting crystals and the other at ~180 °C representing the clearing temperature (Tni). According to Kim and Han,9 PSHQ10 has Schlieren texture at temperatures between Tm2 and Tm-Previously Kim and Han14 demonstrated that, when sheared between two glass plates, an as-cast PSHQ10 specimen having Schlieren texture exhibited banded structure in the direction perpendicular to the shear direction.…”

Section: Domain Texture Of Melt-spun Pshq10mentioning

confidence: 94%

Effect of Thermal History on the Time Evolution of the Structure of a Main-Chain Thermotropic Liquid-Crystalline Polyester

Han¹,

Chang²,

Kim³

1994

Macromolecules

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The effect of thermal history on the time evolution of the structure of a main-chain thermotropic liquid-crystalline polymer, poly[(phenylsulfonyl)-p-phenylene l,10-decamethylenebis(4oxybenzoate)] (PSHQ10), was investigated using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and optical microscopy. For the study, the specimens having the following thermal histories were employed: (a) fully oriented melt-spun fiber, (b) as-cast specimen, and (c) as-cast specimen followed by thermal treatment at 190 °C in the isotropic region. We found that when an as-cast specimen was annealed at 130 °C, it exhibited an intermediate endothermic peak at a temperature (Tmi) between the crystal melting temperature (Tm2) (~120 °C) and the nematic-isotropic transition temperature (Tni) (~180 °C) very soon after the annealing began, but when an as-cast specimen was first heated to 190 °C in the isotropic region followed by annealing at 130 °C, only T^a and Tni appeared until the annealing continued for ~40 h and then Tmi appeared as the annealing continued further. We found, however, that a melt-spun fiber exhibited only Tm2 and Tni until the annealing continued for ~40 h and then Tml appeared as the annealing continued further. By conducting variable heating rate DSC we have concluded

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“…[10,11,30] In the melt at rest, the polydomain structure of the aromatic copolyester shown in Figure 1 is macroscopically unoriented, while the liquid crystalline orientational order is preserved within the nematic domains. [31] Above its melting point, its rigid molecular segments self-assemble into nematic domains of a few micrometers in size. [32] Anisotropy is generated in the melt by shear and extensional flow arising during extrusion through the converging nozzle of the 3D printer.…”

Section: Printing Strategymentioning

confidence: 99%

3D Printing of Flow‐Inspired Anisotropic Patterns with Liquid Crystalline Polymers

Houriet,

Damodaran,

Mascolo

et al. 2023

Advanced Materials

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Anisotropic materials formed by living organisms possess remarkable mechanical properties due to their intricate microstructure and directional freedom. In contrast, human‐made materials face challenges in achieving similar levels of directionality due to material and manufacturability constraints. To overcome these limitations, an approach using 3D printing of self‐assembling thermotropic liquid crystal polymers (LCPs) is presented. Their high stiffness and strength is granted by nematic domains aligning during the extrusion process. Here, a remarkably wide range of Young's modulus from 3 to 40 GPa is obtained during by utilizing directionality of the nematic flow during the printing process. By determining a relationship between stiffness, nozzle diameter, and line width, a design space where shaping and mechanical performance can be combined is identified. The ability to print LCPs with on‐the‐fly width changes to accommodate arbitrary spatially varying directions is demonstrated. This unlocks the possibility to manufacture exquisite patterns inspired by fluid dynamics with steep curvature variations. Utilizing the synergy between this path‐planning method and LCPs, functional objects with stiffness and curvature gradients can be 3D‐printed, offering potential applications in lightweight sustainable structures embedding crack‐mitigation strategies. This method also opens avenues for studying and replicating intricate patterns observed in nature, such as wood or turbulent flow using 3D printing.

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The Morphology of Liquid-Crystalline Polymers and the Possible Consequences for their Rheological Behaviour

Cited by 18 publications

References 49 publications

The effect of shear on thermotropic liquid crystalline polymers

The effect of shear on thermotropic liquid crystalline polymers

Effect of Thermal History on the Time Evolution of the Structure of a Main-Chain Thermotropic Liquid-Crystalline Polyester

3D Printing of Flow‐Inspired Anisotropic Patterns with Liquid Crystalline Polymers

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