Surfactant-Mediated Modulation of Thin Droplets Spreading on a Soft Substrate

Area of Science:

• Fluid Dynamics and Soft Matter Physics

Background:

• Droplet spreading on soft viscoelastic substrates is crucial for biological systems, coatings, and electronics.
• Understanding surfactant effects on droplet dynamics is key to controlling these applications.

Purpose of the Study:

• To model and analyze the spreading behavior of surfactant-laden droplets on soft viscoelastic substrates.
• To investigate the influence of Marangoni and Péclet numbers on spreading dynamics.

Main Methods:

• Utilized lubrication theory to develop a reduced-order model.
• Derived coupled nonlinear spatiotemporal evolution equations for interface tracking.
• Performed parametric investigations on Marangoni and Péclet numbers.

Main Results:

• For perfect wetting, surfactants decrease spreading due to opposing Marangoni stresses.
• Increased Péclet number reduces spreading rate and extent.
• For partial wetting, higher Marangoni numbers enhance spreading by lowering contact angle and reducing viscoelastic braking.

Conclusions:

• Surfactant-driven reduction in viscoelastic braking is the primary mechanism for enhanced spreading in partial wetting scenarios.
• Findings align with recent experimental observations of surfactant-enhanced spreading on soft substrates.