Optical Coherence Tomography Velocimetry for In-Line Processing: The Spherical-to-Wormlike Micelle Transition.

Area of Science:

• Materials Science
• Fluid Dynamics
• Chemical Engineering

Background:

• Personal care products require extensive off-line rheological analysis for quality control.
• Variations in product chemistry necessitate robust monitoring to ensure consumer satisfaction.
• An in-line rheological monitoring system can enhance industrial manufacturing efficiency.

Purpose of the Study:

• To demonstrate optical coherence tomography velocimetry (OCT-V) as a viable in-line method for rheological quality control.
• To assess the performance of OCT-V in monitoring shampoo formulations with varying salt concentrations.
• To establish in-line rheological benchmarks for dynamic product formulation.

Main Methods:

• Utilized optical coherence tomography velocimetry (OCT-V), a noninvasive quasi-elastic light scattering technique.
• Employed an in-line apparatus with infrared light (1315 nm) on a 200 L test rig.
• Measured time-averaged velocity profiles and transient velocity fluctuations in shampoo formulations at controlled flow rates (500 and 1000 L/h).

Main Results:

• OCT-V provided spatially resolved velocity measurements with high accuracy, showing low error (0.4% and 5.6%) in flow rate predictions.
• The standard deviation of transient velocity fluctuations decreased with increasing salt concentration, correlating with rising viscosity.
• Hagen-Poiseuille equation fits to velocity data closely matched imposed flow rates for a 1.1% NaCl shampoo formulation.

Conclusions:

• OCT-V is a promising noninvasive technique for in-line rheological monitoring of dynamically formulated products like shampoos.
• Velocity fluctuation measurements can serve as a reproducible indicator of product quality in industrial settings.
• Integration with pressure drop measurements allows for calculation of constitutive properties like viscosity, optimizing manufacturing processes.