Polydomain model predictions of liquid crystalline polymer orientation in mixed shear/extensional channel flows

Cinader, David K.; Burghardt, Wesley R.

doi:10.1007/s003970000078

Cited by 11 publications

(11 citation statements)

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“…Indeed, such sign changes have generally been found in experiments in this flow geometry [6][7][8][9][10] for a wide range of materials. Evaluation of Ericksen and Larson-Doi model in mixed shearextensional kinematics reveals that the orientation becomes more susceptible to the effects of transverse stretching as k decreases in magnitude [20]; these expectations are born out in the simulations (Fig. 3b), in which smaller k values lead to stronger transverse alignment (more highly negative centerline anisotropy).…”

Section: Parametric Studiesmentioning

confidence: 79%

“…More importantly, its relative simplicity allows for straightforward attack of process flows, something that is currently not possible with more sophisticated theories. Despite its favorable position for simulations of orientation in processing, to date, only limited efforts have been made to use the Larson-Doi model beyond the case of homogeneous shear flow [20].…”

Section: Modeling Strategymentioning

confidence: 99%

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Polydomain model predictions of molecular orientation in isothermal channel flows of thermotropic liquid crystalline polymers

Fang

Burghardt

Bubeck

2008

Polymer Engineering & Sci

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We report process simulations of molecular orientation of liquid crystalline polymers for isothermal channel flows in extrusion. The simulations use a ''polydomain'' model due to Larson and Doi (Larson and Doi, J. Rheol., 35, 539 (1991)), which is implemented by exploiting a nearly exact analogy with a fiber orientation model that is widely used for analysis of composites processing. Simulation results are compared to experimental data previously obtained using a customized X-ray capable extrusion die that allows a wide range of channel flow geometries to be explored. Competition between inhomogeneous shear and extension in these kinematically complex flows has a profound effect on the resulting molecular orientation distributions. We find that the Larson-Doi model successfully predicts most aspects of the experimental observations, demonstrating its utility for process modeling.

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Section: Parametric Studiesmentioning

confidence: 79%

Section: Modeling Strategymentioning

confidence: 99%

Polydomain model predictions of molecular orientation in isothermal channel flows of thermotropic liquid crystalline polymers

Fang

Burghardt

Bubeck

2008

Polymer Engineering & Sci

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“…Recently, there have been a number of efforts toward this aim, typically involving the use of fluidic devices that simulate a processing flow of interest. Examples include channel flows 7 – 9 , cross slot geometries to achieve relatively homogeneous 2D elongation 10 – 13 , contraction/expansion geometries to study axisymmetric entrance and exit flows 6 , 14 – 16 , and flows around obstacles 17 . These studies highlight a number of challenges and limitations inherent to the use of fluidic devices for flow-SANS measurements.…”

Section: Introductionmentioning

confidence: 99%

Probing flow-induced nanostructure of complex fluids in arbitrary 2D flows using a fluidic four-roll mill (FFoRM)

Corona¹,

Ruocco²,

Weigandt³

et al. 2018

Sci Rep

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Engineering flow processes to direct the microscopic structure of soft materials represents a growing area of materials research. In situ small-angle neutron scattering under flow (flow-SANS) is an attractive probe of fluid microstructure under simulated processing conditions, but current capabilities require many different sample environments to fully interrogate the deformations a fluid experiences in a realistic processing flow. Inspired by recent advances in microfluidics, we present a fluidic four-roll mill (FFoRM) capable of producing tunable 2D flow fields for in situ SANS measurements, that is intended to allow characterization of complex fluid nanostructure under arbitrary complex flows within a single sample environment. Computational fluid dynamics simulations are used to design a FFoRM that produces spatially homogeneous and sufficiently strong deformation fields. Particle tracking velocimetry experiments are then used to characterize the flows produced in the FFoRM for several classes of non-Newtonian fluids. Finally, a putative FFoRM-SANS workflow is demonstrated and validated through the characterization of flow-induced orientation in a semi-dilute cellulose nanocrystal dispersion under a range of 2D deformations. These novel experiments confirm that, for steady state straining flows at moderate strain rates, the nanocrystals orient along the principal strain-rate axis, in agreement with theories for rigid, rod-like Brownian particles in a homogeneous flow.

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“…Gentzler and coworkers (2000) used spatially resolved nuclear magnetic resonance spectroscopy to study the velocity distribution in entry flow of a LCP and found unusual off‐center maxima that they attributed to textural elasticity. Cinader and Burghardt (2000a) used wide‐angle X‐ray to study LCP orientation development in planar contraction and expansion, and they found qualitative agreement in a simulation using the Larson‐Doi model for polydomain LCPs (Cinader and Burghardt, 2000b). Transient simulations using continuum models of liquid‐crystalline polymers in simple shear flows show a great deal of complex texture evolution, but they are unable at present to replicate defect‐driven textures characteristic of real LCPs, where the correlation lengths for order are independent of the geometric scale of the system (Kupferman et al, 2000; Sgalari et al, 2003); hence, much remains to be done before predictive calculations in complex flows will be possible.…”

Section: Anistropic Liquidsmentioning

confidence: 95%

Fifty years of non‐Newtonian fluid dynamics

Denn

2004

AIChE Journal

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Polydomain model predictions of liquid crystalline polymer orientation in mixed shear/extensional channel flows

Cited by 11 publications

References 0 publications

Polydomain model predictions of molecular orientation in isothermal channel flows of thermotropic liquid crystalline polymers

Polydomain model predictions of molecular orientation in isothermal channel flows of thermotropic liquid crystalline polymers

Probing flow-induced nanostructure of complex fluids in arbitrary 2D flows using a fluidic four-roll mill (FFoRM)

Fifty years of non‐Newtonian fluid dynamics

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