Molecular Dynamics and Rheological Properties of Liquid Crystalline Polymer in an Electric Field

Lee, Young Chul; Huh, Jung Do; Chung, In Jae

doi:10.1295/polymj.22.295

Cited by 6 publications

(3 citation statements)

References 24 publications

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“…In an effort to overcome disadvantages of suspension ER fluids, researchers in the past decade have begun to examine homogeneous (nonparticulate) ER fluids based on liquid crystals, especially liquid crystalline polymers (LCPs). The ER effect has been explored in main-chain LCPs with flexible spacers between mesogens, 5 in side-chain LCPs with a flexible backbone having attached mesogens, [5][6][7] and in solutions of rigid rod main-chain LCPs, 8,9 especially those having a helical structure. [10][11][12][13] The ER effect observed in LCPs arises from the anisotropy of the mesogen shape and of the attendant electrical properties.…”

Section: Introductionmentioning

confidence: 99%

Steady-State Electrorheology of Nematic Poly(n-hexyl isocyanate) Solutions

Tse

Shine

2000

Macromolecules

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The steady-state electrorheological (ER) properties of unidomain nematic poly(n-hexyl isocyanate) (PHIC) solutions in p-xylene have been experimentally characterized and theoretically modeled with a two-dimensional modified version of Doi's theory of liquid crystalline polymer rheology. This molecular model allows the prediction of ER fluid behavior directly from properties of the component polymer and solvent. Optical conoscopic measurements confirmed that high applied electric fields align the PHIC molecules in the field direction, so the high-field viscosity approaches the transverse Miesowicz viscosity, ηc. The PHIC solutions exhibited many desired ER properties comparable to strong suspension ER fluids, such as a transmitted shear stress of 16 kPa and a viscosity enhancement of 180 times. At low shear rates, quantitative agreement between predictions and data at high fields was obtained using a single adjustable parameter, the rotational diffusivity, D r. At high shear rates, an additional parameter, β, was required to account for the viscous contributions to the stress tensor. The temperature dependence of the solution electrorheology was predicted to come exclusively from that of the solvent viscosity.

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Section: Introductionmentioning

confidence: 99%

Steady-State Electrorheology of Nematic Poly(n-hexyl isocyanate) Solutions

Tse

Shine

2000

Macromolecules

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“…The nematic director can be oriented through the application of an external electric or magnetic field . Lee and co-workers extracted the rotational diffusivity of poly( p -phenylene terephthalamide) (PPTA) in sulfuric acid solutions from measurements of η b in Poiseuille flow under an electric field …”

Section: Introductionmentioning

confidence: 99%

“…32 Lee and co-workers extracted the rotational diffusivity of poly(p-phenylene terephthalamide) (PPTA) in sulfuric acid solutions from measurements of η b in Poiseuille flow under an electric field. 33 In this work, we have adopted a similar procedure to extract D r from η c , but without the shortcomings of the decoupling approximation used by Marrucci. 29 Steady-state ER characterization of simple shear flows with an applied electric field perpendicular to the shear direction of nematic PHIC solutions have shown that the viscosity increases sigmoidally above a threshold electric field until it reaches a plateau or maximum value.…”

Section: Introductionmentioning

confidence: 99%

Molecular Weight Dependence of the Rotational Diffusivity of Rodlike Polymers in Concentrated Nematic Solutions

2005

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The dynamics of rodlike polymer molecules in the nematic phase are mainly controlled by the rotational diffusivity, D r, which is highly sensitive to molecular weight. However, few experimental determinations of D r for polymer solutions at concentrations in the nematic phase have been made. We invoke Doi's theory of liquid crystalline polymer rheology to extract D r from experimental measurements of the transverse Miesowicz viscosity, ηc, of nematic solutions. Transverse Miesowicz viscosities were measured for a series of poly(n-hexyl isocyanate) (PHIC) polymers at fixed dimensionless concentration (c/c* = 1.25) in p-xylene, by orienting the director with a high dc electric field. The rotational diffusivity of PHIC was found to be independent of shear rate and proportional to M w -4.95±0.29. This scaling is in excellent agreement with Doi's molecular theory, which predicts that D r scales as M -5 at fixed c/c*. The experimental values of D r were compared with theoretical values calculated a priori from molecular dimensions and the solution concentration. The numerical constant β which multiplies Doi's predicted D r was found to be of order 101 for the nematic PHIC solutions, in contrast with values of order 103 reported for semidilute solutions of rodlike molecules.

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Ordering of liquid crystalline solutions of rigid‐rod aramids using mechanical shearing and electric‐field poling

Weder¹,

Glomm²,

Neuenschwander³

et al. 1995

Macro Chemistry & Physics

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2',5'-Diamino-4-(dimethylamino)-4'-nitrostilbene was polymerized with terephthaloyl dichloride and 2,6-difluoroterephthaloyl dichloride in a low-temperature solution polycondensation to give two novel, fully aromatic rigid-rod polyamides. Nematic solutions of these polymers were processed into fibers and films that were characterized by wide-angle X-ray diffraction measurements. A post-spin annealing process was employed to enhance the chain orientation in the fibers. The dominating crystal structure was found to be similar to "modification 11" of the fibers from poly@-phenyleneterephthalamide), but the fibers do not suffer a comparable structural transformation upon heat treatment. A corona-discharge poling process gave rise to a remarkable gain in average chain orientation in the films. Again the crystal structure was found to be similar to "modification 11". The aramids investigated in this work represent a new approach to the design of liquid-crystalline rigid-rod polymers, where different mechanisms of orientation can be combined. In the nematic phase, the rigid-rod molecules form highly oriented domains that can be oriented using mechanical processes such as shearing. In addition the stilbene units that are fixed in the polymer backbone with their dipole moments oriented transverse to the main chain can be oriented in an electric field. The combination of both orientation mechanisms seems to cause a synergistic effect, probably since each affects different levels of the polymer microstructure in the solid.

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Molecular Dynamics and Rheological Properties of Liquid Crystalline Polymer in an Electric Field

Cited by 6 publications

References 24 publications

Steady-State Electrorheology of Nematic Poly(n-hexyl isocyanate) Solutions

Steady-State Electrorheology of Nematic Poly(n-hexyl isocyanate) Solutions

Molecular Weight Dependence of the Rotational Diffusivity of Rodlike Polymers in Concentrated Nematic Solutions

Ordering of liquid crystalline solutions of rigid‐rod aramids using mechanical shearing and electric‐field poling

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