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  • 1
    Electronic Resource
    Electronic Resource
    Orienting properties of discotic nematic liquid crystals in Jeffrey-Hamel flows (1991)
    Springer
    Rheologica acta 30 (1991), S. 77-88 
    Details
    ISSN: 1435-1528
    Keywords: Discotic-nematic liquid crystals ; Jeffrey-Hamel flows ; orienting properties ; reactive parameter
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The orienting properties of incompressible discotic nematic liquid crystals for creeping flows between converging and diverging planar walls (Jeffrey-Hamel) are analyzed using the Leslie-Ericksen theory. The dependence of director orientation on the reactive parameter λ and the flow kinematics is presented. Closed form stationary solutions for the director orientation are found when elastic effects are neglected. Stationary numerical solutions for the velocity and director fields using the full Leslie-Ericksen theory are presented. The director field in converging flow is characterized by azimuthal (radial) centerline orientation, by being asymmetric with respect to the azimuthal (radial) direction, and by having an allowed orientation range that spans two half-quadrants (full quadrants). In the limiting case of perfectly flat disk (λ ⇒ −∞) the flow-induced director orientation in converging flow is the azimuthal direction, while in diverging flow the director rotates by a full n radians. By reducing the vertex angle between the walls to vanishingly small values, converging flow solutions properly reduce to those of flow between parallel plates, but diverging flows are expected to lead to a new instability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00366797
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  • 2
    Electronic Resource
    Electronic Resource
    Rheological predictions of a transversely isotropic fluid model with extensible microstructure (1993)
    Springer
    Rheologica acta 32 (1993), S. 447-456 
    Details
    ISSN: 1435-1528
    Keywords: Semiflexible nematic polymers ; transversely isotropic liquid ; extensible director ; shear flow alignment ; rheological predictions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract A continuum extensible director theory was formulated to describe the isothermal, incompressible flow of uniaxial rodlike semiflexible liquid crystalline polymers. The model is strictly restricted to material that flow-align in shear, and that, in the absence of flow, are sufficiently far from the nematic-isotropic phase transition. The microstructure of the continuum is described by a variable length director, but the extensibility is finite. The model is an extension of the TIF (Transversely Isotropic Fluid) model of Ericksen (1960). The thermodynamic restrictions on the model parameters are found using the non-negative definiteness of the entropy production. The rheological material functions predicted by the model are calculated for steady simple shear and steady uniaxial extensional flows. In the rigid rod limit the model predictions agree with those of the TIF model, and for the finite extensibility case the model predictions are in agreement with those associated with flexible isotropic polymers: strong non-Newtonian shear viscosity, positive first normal stress differences, recoverable shear of order one, negative second normal stress differences, and a maximum in the steady uniaxial extensional viscosity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396175
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  • 3
    Electronic Resource
    Electronic Resource
    Ordering effects in shear flows of discotic polymers (1993)
    Springer
    Rheologica acta 32 (1993), S. 207-217 
    Details
    ISSN: 1435-1528
    Keywords: Discotic nematic polymers ; shear flows ; ordering effects ; orienting regimes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The tensorial mechanical model of Farhoudi and Rey (1993) for uniaxial, rodlike, spatially homogeneous and monodomain nematics is modified to describe the microstructural response of discotic nematic network polymers in rectilinear simple shear flow. The particular topological features of the discotic phase are taken into account by a proper modification of the phenomenological parameters. Asymptotic and numerical solutions of the microstructural balance equations indicate the appearance of tumbling, oscillating, and stationary flow regimes as the strength of shear increases, as is the case for rod-like nematic polymers (Marrucci, 1991). The tumbling-oscillating transition is characterized by a diverging tumbling function λ, while the oscillating-stationary transition is characterized by a single steady value λ smaller than —1. The stable steady states of the stationary regime are shown to belong to the family of unstable isotropic solutions that exist at small shear rates, and are characterized by a director angle close to, but less than +90° to the flow direction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00434185
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