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Homeotropic to planar transition backflow and kickback effects

2 Homeotropic to planar transition backflow and kickback effects The other two geometries used in the Freedericksz experiment are more interesting as they result in a new effect, namely, hydrodynamic flow induced by orientational deformation. This is the inverse of the more familiar property of flow alignment that has been discussed at length in previous sections. [Pg.162]

The translational velocity (3.8.6) has two components in the simplest case one linear in z and the other oscillatory, the wavelength of the latter diminishing with increasing value of the final field H. The transient velocity profile is illustrated schematically in fig. 3.8.1. The effect of this backflow is to relax the constraints, i.e., to reduce the apparent viscosity. [Pg.163]

In the planar to homeotropic transition (fig. 3.4.1(a)) backflow effects are not usually so pronounced near the threshold. In this geometry, the torque exerted by the director on an elementary volume of the fluid is [Pg.163]

The marked difference in the relaxation rates for the two geometries at higher fields confirms the existence of backflow as predicted by the Leslie equations (fig. 3.8.3). Backflow has also been studied by direct observation of the motion of disclination walls separating two regions of opposite tilt in a film which is subject to a magnetic field.  [Pg.165]

It is instructive to consider the geometry of fig. 3.4.1 (a) and to examine the relaxation when the field is switched off from H io zero. Clark and Leslie have analysed this problem theoretically and have presented the equations in a form that reduces considerably the computational effort required for making detailed predictions in any practical situation. Using [Pg.165]




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And planarity

Backflow

Backflow effect

Homeotropic

Kickback effect

Transition effects

Transition planar

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