Shear flows of nematic polymers. I. Orienting modes, bifurcations, and steady state rheological predictions
作者:
Yalda Farhoudi,
Alejandro D. Rey,
期刊:
Journal of Rheology
(AIP Available online 1993)
卷期:
Volume 37,
issue 2
页码: 289-314
ISSN:0148-6055
年代: 1993
DOI:10.1122/1.550444
出版商: The Society of Rheology
关键词: Liquid crystals, polymer;Nematic polymers;Orientation;Bifurcations, in liquid crystalline polymers;NEMATIC CRYSTALS;POLYMERS;SHEAR FLOW;BIFURCATION;LIQUID CRYSTALS;INCOMPRESSIBLE FLOW;ORIENTATION;TENSORS;VISCOELASTICITY
数据来源: AIP
摘要:
A continuum tensorial theory was formulated to describe the isothermal, incompressible flow of uniaxial rodlike nematic liquid crystalline polymers. The tensor theory was reduced to a vector theory that describes the microstructure of the uniaxial phase by specifying the director orientation and the scalar order parameter. The reduction establishes useful relationships between this theory and the Leslie and Ericksen theory. The model was solved for a given steady simple shear flow, assuming spatial homogeneity. Two types of orienting modes are predicted: (a) the simple aligning mode, in which the microstructure reaches a stable shear dependent steady state for all shear rates, and (b) the complex mode, which at sufficiently high nematic potentials exhibits three flow regimes (tumbling, oscillating, and stationary) according to the strength of the imposed shear flow. For sufficiently low nematic potentials, the complex mode predicts the existence of a single stationary mode. Bifurcation theory was used to fully characterize the existence and transitions between the three regimes of the complex mode. Guidelines for future simplifications of the constitutive equations are given. The frequently reported changes in the sign of normal stress differences with shear rate are captured by the model.
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