A Numerical Study of Micro-Droplet Spreading Behaviors on Wettability-Confined Tracks Using a Three-Dimensional...

Area of Science:

• * Microfluidics
• * Fluid Dynamics
• * Computational Physics

Background:

• * Wettability-confined tracks are crucial for pumpless droplet transport in open-surface microfluidic devices.
• * Previous experimental work has demonstrated droplet spreading on such tracks.

Purpose of the Study:

• * To investigate microdroplet spreading behaviors on wettability-confined tracks using a 3D phase-field lattice Boltzmann model.
• * To analyze the influence of track divergence angle on droplet spreading dynamics.
• * To explore droplet spreading on inclined tracks.

Main Methods:

• * Development and application of a three-dimensional phase-field lattice Boltzmann model.
• * Simulation of microdroplet spreading on horizontal and inclined wettability-confined tracks.
• * Parametric study of track divergence angles and droplet volume conservation.

Main Results:

• * Successfully reproduced experimental findings of three distinct droplet spreading stages (initial, intermediate, final).
• * Demonstrated that track divergence generates Laplace pressure gradients and capillary forces driving droplet movement.
• * Established a linear relationship between divergence angle and capillary force, affecting spreading speed and stage transitions.
• * Proposed a power law relation between divergence angle and droplet spreading to identify the onset of the final decelerating stage.

Conclusions:

• * Track divergence angle is a key parameter controlling microdroplet spreading speed and behavior on wettability-confined tracks.
• * Droplet spreading on inclined tracks is feasible only when initial capillary force overcomes gravitational components.
• * The developed model accurately simulates and explains droplet spreading phenomena in microfluidic systems.