Electrokinetic and electro-elastic instabilities in viscoelastic microfluidic flows: suppression and augmentation in...

Area of Science:

• Microfluidics
• Rheology
• Non-Newtonian fluid dynamics

Background:

• Viscoelastic fluids are transported in microfluidic systems using electric fields.
• Two instabilities, electro-elastic (EEI) and electrokinetic (EKI), can arise, promoting mixing.
• Fluid viscoelasticity's effect on mixing efficiency, particularly in T-junctions, is complex.

Purpose of the Study:

• To investigate the non-monotonic relationship between fluid viscoelasticity and mixing efficiency in electrokinetically driven microflows.
• To differentiate the flow structures and origins of EEI and EKI.
• To provide insights for optimizing mixing in microfluidic devices.

Main Methods:

• Numerical simulations of viscoelastic fluid flow in a microfluidic T-junction.
• Analysis of flow instabilities, including EEI and EKI.
• Application of dynamic mode decomposition (DMD) to characterize instability modes.

Main Results:

• Increasing viscoelasticity initially suppresses EKI and reduces mixing.
• Beyond a critical Weissenberg number, EEI emerges, leading to increased mixing.
• A non-monotonic relationship between mixing efficiency and Weissenberg number was observed.
• EEI and EKI exhibit distinct flow structures and origins.

Conclusions:

• Fluid viscoelasticity plays a crucial, non-monotonic role in modulating flow instabilities and mixing in electrokinetic microflows.
• Dynamic mode decomposition effectively characterizes instability modes and their impact on mixing.
• Tuning fluid properties and operating conditions can optimize mixing efficiency.