Document 4207Q258 V3.00 January 2018
Page 10 of 30
Chirascan Couette Cell LD Accessory User Manual
Figure 1.2: Two-dimensional representation of a shearing motion
Shearing can cause large particles in the liquid to align or deform. For example rigid, rod-like, particles such
as carbon nanotubes and glass fibers, will align, whereas vesicles, micelles and flexible polymers will deform
from their equilibrium conformations, extending in the direction of shear. Linear dichroism is then used to
determine the direction of net electron transfer in an absorbed chromophore relative to the shear direction, and
thereby to the alignment direction of the absorbing species or membrane.
A schematic of the Couette cell used in the accessory is shown in Figure
. In the figure, the sample is shown
in blue, the light path in violet. The black arrows indicate the standard direction of rotation of the outer cylinder,
which is anticlockwise (counterclockwise) when viewed from above.
Figure 1.3: Schematic of the Couette cell; top view is shown on the right with the light path in violet
The sample is therefore sheared between the two cylinders in the cell, at a rate proportional to the angular
velocity of the rotor,
. The angular velocity is measured in radians per second (rad s
-1
), and is equal to 2
x
the rotational speed in revolutions per second (rps). The shear rate is measured in reciprocal seconds (s
-1
1/s).
The diameter of the rotor in the cell is 9.55 mm, and of the stator is 9.05 mm; the annular gap is thus 0.25 mm,
but note that since the light passes though the sample twice, the pathlength is 0.5 mm (these dimensions may
vary slightly, but will always be known precisely).
Outer cylinder
(rotor)
Inner cylinder
(stator)
Sample
Outer cylinder
(rotor)
Inner cylinder
(stator)
Sample
Light path
