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Surfactant-Enhanced Spreading on Solids: Roles of the Surface Tension Gradient, Spreading Contact Angle, and
Jongju Lee1, Sohail Murad1, Alex Nikolov1
1Department of Chemical and Biological Engineering, Illinois Institute of Technology, Chicago, Illinois 60616, United States.
Langmuir : the ACS Journal of Surfaces and Colloids
|December 16, 2024
Summary
Optimizing surfactant-enhanced spreading on solids requires a specific initial contact angle of 60° for maximum efficiency. This study models the surface tension gradient to understand and improve spreading rates for applications like oil spill cleanup.
Area of Science:
- Colloid and Surface Science
- Fluid Dynamics
- Materials Science
Background:
- Surfactant-enhanced spreading on solids is crucial for technological applications but not fully understood.
- Spontaneous spreading relies on surface tension gradients (Marangoni stresses) for rapid, large-area coverage.
- Previous work identified an optimum substrate wettability around 60° for spreading.
Purpose of the Study:
- To explain the requirement of a 60° contact angle for optimal surfactant-enhanced spreading.
- To develop a model for calculating the surface tension gradient over time.
- To investigate the influence of surface tension gradient, viscosity, and wettability on spreading dynamics.
Main Methods:
- Analysis of experimental data including spreading rate, contact angle, and droplet radius.
- Development of an equation to estimate the surface tension gradient.
- Observation of fingering instability as evidence of Marangoni stress effects.
Main Results:
- The surface tension gradient significantly impacts spreading rate more than the contact angle.
- An equation was derived to calculate the time-dependent surface tension gradient.
- Fingering instability confirms the dominant role of the surface tension gradient.
Conclusions:
- Optimal surfactant-enhanced spreading on solids is achieved at an initial contact angle of 60° ± 5°.
- The surface tension gradient is the primary driver of enhanced spreading dynamics.
- Understanding these principles can optimize applications in oil spill remediation and pesticide delivery.
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