Viscous Fingering Induced by a pH-Sensitive Clock Reaction

Area of Science:

• Chemical Engineering
• Fluid Dynamics
• Polymer Science

Background:

• Viscous fingering is a fluid instability occurring at interfaces between fluids of different viscosities.
• Chemical reactions can alter fluid properties, potentially influencing interfacial instabilities.
• Hele-Shaw cells are standard experimental tools for studying fluid dynamics and instabilities.

Purpose of the Study:

• To experimentally demonstrate viscous fingering instability induced by a pH-changing clock chemical system.
• To investigate how changes in viscosity, driven by a chemical reaction, destabilize fluid displacement.
• To analyze the impact of chemical parameters on fingering instability and compare with simulations.

Main Methods:

• Utilizing a Hele-Shaw cell to observe fluid displacement.
• Employing a formaldehyde-sulfite clock reaction to induce pH changes.
• Displacing a low-viscosity formaldehyde solution with a more viscous sulfite and poly(acrylic acid) solution.
• Analyzing the influence of chemical parameters and comparing experimental results with numerical simulations.

Main Results:

• A pH-changing clock chemical system was experimentally shown to induce viscous fingering instability.
• The chemical reaction in the contact zone increased local viscosity, destabilizing the displacement.
• Observed fingering instability was influenced by variations in chemical parameters.

Conclusions:

• pH-triggered viscosity changes in reactive solutions can induce viscous fingering instability.
• The formaldehyde-sulfite clock reaction provides a mechanism to control and study this instability.
• Experimental findings align with numerical simulations, validating the model.