Trade Off between Hydrodynamic and Thermodynamic Forces at the Liquid-Liquid Interface

Area of Science:

• Fluid Dynamics
• Thermodynamics
• Materials Science

Background:

• Viscous fingering (VF) is an instability in fluid dynamics.
• Partially miscible fluid systems exhibit coupled phase separation and VF.
• Thermodynamics (Margules parameter, concentration) and kinetics (viscosity) govern these systems.

Purpose of the Study:

• To investigate viscous fingering instability in partially miscible binary systems.
• To explore the trade-offs between hydrodynamic and thermodynamic effects.
• To understand the influence of concentration and Margules parameter on phase separation and instability dynamics.

Main Methods:

• Nonlinear numerical simulations using the modified Cahn-Hilliard-Hele-Shaw equation.
• High-resolution simulations performed with COMSOL Multiphysics software.
• Selection of concentrations based on Gibb's free energy curves (outside spinodal/binodal, within binodal, within spinodal).

Main Results:

• Thermodynamic forces are strongly dependent on mixture concentration.
• Rapid phase separation and faster droplet formation occur when concentration is within the spinodal region.
• Correlation between fractal dimension and system dynamics was investigated.

Conclusions:

• Spatiotemporal studies reveal a competition between hydrodynamic and thermodynamic forces.
• Insights into the kinetics of decomposition and growth of interfacial instabilities are provided.
• Concentration plays a critical role in modulating VF instability in partially miscible systems.