DORA - Rheology
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Transcript DORA - Rheology
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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