Nematodynamics stress

Leslie, F.M. Introduction to nematodynamics. In Dunmur, D., Fukuda, A., Luckhurst, G., INSPEC (eds.) Physical Properties of Liquid crystals Nematics, pp. 377-386, London (2001). Parodi, O. Stress tensor for nematic liquid crystals. J. Phys. (Paris) 31, 581-584 (1970) Miesowicz, M. The three coefficients of viscosity of anisotropic liquids. Nature 158, 27 (1946) Influence of the magnetic field on the viscosity of para-azoxyanisole. Nature 136, 261 (1936). 

This effect has mostly been observed for lyotropic LCPs, sometimes also for thermotropic ones. The existence of region I in Figure 11.1 is explained by the formation of texture, a domain structure observed in many, mostly lyotropic LCPs. The texture occurs during relaxation when the stress levels are very low, that is, when approaching the rest state. Such a three-region flow curve was first observed in Ref. [50] and explained theoretically for lyotropic LCPs in Refs [51, 52] (see also Refs [4, 5, 53]). These theoretical descriptions are typically complementary to the more fundamental monodomain nematodynamic theories of both the molecular and the continuous types. 

Due to the presence of the second term on the right-hand side of (7.27), the tensor rj is not symmetric. Since in the equation of motion only its divergence Vyct matters, we can construct a symmetric stress tensor that gives exactly the same value of divergence [11, 12, 15]. The symmetric stress tensor guarantees the conservation of local angular momentum. Therefore asymmetry of is not really a problem in nematodynamics. 

The negative first normal stress difference (Ni) could not be predicted by Leonov s nematodynamics model. The values of Ni for filled LCPs are shown as a trend beyond 10 s . ... 

Leonov viscoelastic nematodynamics model was chosen for rheological simulation of TLCPs. The simulated viscosities have been compared with experimentally measured viscosity data, indicating a good fit in the shear rate range of 10-2000 s In the low shear rate region, the model did not predict negative normal stress difference for filled TLCPs. For unfilled TLCPs, good comparison has been observed between the simulated values of Ni and the experimental data. 

In conclusion we observe that despite the rather well-understood interplay between bosurface stresses in defining nematodynamics, the design and development of reliable, routine experiments yielding the complete, canonical set of viscosity coefficients encounters a number of limitations and obstacles which are yet to be satisfactorily solved. 

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