RHEOLOGICAL TESTING TECHNIQUES FOR COATING APPLICATIONS

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Dynamic Optical Rheo Analyzer (DORA)
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DORABackground
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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DORABackground
Polarization state generator PSG
Light Source L
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 ApplicationsLiquid Crystal
Although the Dichroism decreases the orientation
angle increases due to the alingment of the
crystals in flow direction
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DORA ApplicationsShear Banding of a Micellar
Solution
Increase in Birefringence at point where stress
curve flattens, i.e. onset of shear banding
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Particle Image Velocimetry (PIV)
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Particle Image Velocimetry (PIV)C-LTD70/PIV
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Rheo PIVParticle 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 PIVExample Shear Banding of Micellar
Solutions
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Flow Curve of Gold Particles suspended in Acetone
Reynolds Number Re gt 1000 165 s-1
Onset of Taylor Vorticities Ta gt 41.2 22
s-1
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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
Voltage application DC or AC voltage
Dielectric Induction of an - electric
field -
LCR meter
Current
Measurement of the flowing current