Confined flows of a polymer microgel

Area of Science:

• Rheology
• Soft Matter Physics
• Fluid Dynamics

Background:

• Polymer microgels exhibit complex flow behavior.
• Understanding flow under confinement is crucial for microfluidic applications.
• Bulk rheology may not accurately predict confined flow.

Purpose of the Study:

• To investigate the influence of confinement on polymer microgel (Carbopol) flow.
• To compare bulk rheological predictions with experimental measurements in microchannels.
• To characterize confinement effects and determine relevant length scales.

Main Methods:

• Bulk rheology measurements using a rheometer.
• Particle tracking velocimetry (PTV) to measure velocity profiles in microchannels.
• Analysis using a non-local fluidity model.

Main Results:

• Significant disagreement between bulk rheology predictions and measured velocity profiles in microchannels.
• Successful analysis of confined flow using a non-local fluidity model.
• Determination of a cooperativity length scale (ξ) comparable to microgel structure size.
• Confinement effects observed in rheological measurements under varying gap conditions.
• Consistent length scale for rearrangements evidenced by complementary experiments.

Conclusions:

• Confinement profoundly impacts polymer microgel flow, deviating from bulk predictions.
• A non-local fluidity model effectively describes confined microgel dynamics.
• A characteristic cooperativity length scale governs flow rearrangements under confinement.