Dynamic Optical Rheo
Analyzer (DORA)
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DORA
Background
Dynamic Optical Rheo Analyzer (DORA)
Gives structural information simultaneously with
the rheological measurements
Optical Methods used with DORA:
Birefringence and Dichroism
Optical Anisotropy:
Orientation and deformation of the
microstructure cause anisotropy in the
refractive index, i.e. it is a tensor.
Makes use of polarization of light.
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DORA
Background
Light
Source
L
Polarization
state generator
PSG
Sample
S
Polarization
state analyzer
PSA
Detector
D
Calculation with Stokes Vector and Mueller Matrices:
SD = MPSA  MSample  MPSG  S0
S0
: Stokes Vector of the incoming light
MPSG
: Müller Matrix of the polarizer
MSample : Müller Matrix of the sample
MPSA
: Müller Matrix of the analyzer
SD
: Stokes Vector of the light falling on the detector
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DORA – Applications
Liquid Crystal
Although the Dichroism decreases the orientation angle increases due to the alingment
of the crystals in flow direction
-4
1,200
40°
5·10
1/s
30°
-4
4·10
1,000
20°
-4
3·10
900
-4
2·10
800
10°
Liquid cristall step rate
-4
0°
.
opt
-10°
-20°
700
10
600
0
500
.
n'
n''
-4
-10
400
300
n''
-4
opt
-3·10
200
-40°
-50°
n'
-4
-2·10
-30°
Birefringence/Dichroism LC
-4
100
-4·10
0
-5·10
-4
0
50
100
Time t
150
s
200
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DORA – Applications
Shear Banding of a Micellar Solution
Increase in Birefringence at point where stress curve flattens, i.e. onset of shear banding
100
-5
3·10
Pa
-5
2.5·10
10
-5
2·10
NaCy Flow curve 9
-5
1.5·10
n'
Birefringence NaCy
n'
1
Birefringence NaCy Smoothing 1
-5
10
n'
-6
5·10
0.1
1
10
100
1/s
0
1,000
.
Shear Rate
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Particle Image Velocimetry
(PIV)
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Particle Image Velocimetry (PIV)
C-LTD70/PIV
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Rheo – PIV
Particle Imaging Velocimetry
Particle Imaging Velocity (PIV)
 A high power laser and optical
arrangement produce a light sheet.
 The particles in the fluid scatter the
light.
 The scattered light that is detected by
the camera.
 In order to measure the velocity, at least
two exposures are needed.
 Calculation of displacement vectors
 The flow field through the whole gap in
a concentric cylinder geometry can be
measured.
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Rheo – PIV
Example: Shear Banding of Micellar Solutions
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Flow Curve of Gold Particles suspended in
Acetone
4
Reynolds Number
Re > 1000
 = 165 s-1
mPa·s
3
Onset of Taylor Vorticities
Ta > 41.2
 = 22 s-1
2.5
2
1.5
1
0.5
0
1
10
Shear Rate
100
1/s
1,000
.
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CTD Eye for UXF and SER
 In UXF and SER the sample is not centered at the middle of the CTD
 Active sample size is small strip
 Special Optics to focus directly on the sample
 Observed sample size: 10x12m; Image size: 1/3” (4.7x3.6mm)
 Luminera Camera (Lm075) with 1/3” or any other camera with C-mount
 CTD is extended in order that the camera sees the middle of the sample
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Dielectric Spectroscopy: The measurement
 Electrical current flowing through a sample as a response to an alternating electric
field is measured as a function of the field frequency
 Dielectric spectrum gives information on structure and behavior of the material
Voltage application
+
Dielectric
+
Induction of an
- electric field -
Voltage
DC or AC voltage
LCR meter
Current
Measurement of the
flowing current
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