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Published on: September 9, 2022
Role of base flows on surfactant-driven interfacial instabilities
1Department of Chemical Engineering, National Cheng Kung University, Tainan 701, Taiwan.
Summary
Base flows significantly impact interfacial stability in surfactant-laden thin films. The interplay between external forces and interfacial shear dictates stability, revealing diverse flow behaviors and instability pathways.
Area of Science:
- Fluid dynamics
- Interfacial phenomena
- Surfactant transport
Background:
- Interfacial flows with surfactants are crucial in many industrial applications.
- Understanding the stability of these flows is essential for process optimization.
- Base flow conditions can significantly influence interfacial dynamics.
Purpose of the Study:
- To investigate the effect of base flows on interfacial stabilities in thin-film flows with surfactants.
- To analytically unravel the origins of stability and instability.
- To establish a generalized criterion for the onset of instability.
Main Methods:
- Utilized a thin-film flow model to simulate various base-flow conditions.
- Analyzed long-wave perturbations governing interface and surfactant concentration evolution.
- Identified stability modes and characterized them by force ratios.
Main Results:
- Demonstrated diverse stability states (neutral, conditionally stable/unstable, stable, unstable) determined by base flow.
- Identified two primary modes of stability: interface and surfactant modes.
- Showed that base flow has a dual role: interfacial shear destabilizes, while external force stabilizes.
Conclusions:
- The stability of surfactant-laden thin films is highly sensitive to base flow characteristics.
- A competition between destabilizing interfacial shear and stabilizing external forces determines overall stability.
- A generalized instability onset criterion was established for one- and two-fluid systems.
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