Optical coherence tomography velocimetry of colloidal suspensions

Area of Science:

• Rheology and Fluid Dynamics
• Optical Measurement Techniques
• Colloidal Science

Background:

• Complex fluids exhibit low shear rate motion challenging traditional measurement techniques.
• Optical coherence tomography velocimetry (OCTV) offers non-invasive flow measurement.
• Existing OCTV methods have limitations in sensitivity and applicability to opaque fluids.

Purpose of the Study:

• To enhance the sensitivity and applicability of OCTV for complex fluid systems.
• To improve signal-to-noise ratios in OCTV measurements, particularly for optically opaque samples.
• To extend the measurable range of low shear rates in complex fluid dynamics.

Main Methods:

• Combined optical coherence tomography velocimetry with a rheometer and optical modulation.
• Developed a novel interferometer design for improved signal-to-noise ratio.
• Applied the enhanced OCTV system to study sterically stabilized PVP and polystyrene colloidal spheres.

Main Results:

• Achieved a measurable range of shear velocities down to ~40 μm s(-1), an order of magnitude improvement.
• Demonstrated successful application to optically opaque colloidal suspensions.
• Quantified velocity fluctuations across the rheometer gap, aiding in the classification of flow phenomena.

Conclusions:

• The enhanced OCTV system significantly increases sensitivity to low shear rate motion in complex fluids.
• The improved technique is effective for optically opaque colloidal suspensions, revealing shear banding behavior.
• OCTV provides valuable insights into velocity fluctuations, aiding the study of unsteady or turbulent phenomena in complex fluids.