Simulating droplet motion on virtual leaf surfaces.

Area of Science:

• Fluid Dynamics
• Agricultural Science
• Surface Science

Background:

• Understanding agricultural spray retention on plant foliage is crucial for effective crop protection.
• Droplet dynamics, including coalescence and movement, significantly impact spray deposition and efficacy.
• Previous models have not fully captured the complex interplay of forces governing droplet behavior on realistic leaf surfaces.

Purpose of the Study:

• To simulate and analyze the motion and retention of agricultural spray droplets on a virtual cotton leaf surface.
• To investigate the influence of substrate curvature, chemical defects, and droplet coalescence on spray behavior.
• To elucidate the primary driving forces behind droplet movement and their implications for spray coating.

Main Methods:

• A curvilinear thin film model, incorporating a disjoining pressure term, was adapted from existing fluid mechanics research.
• Simulations were performed on a virtual cotton leaf surface reconstructed from digitized scan data.
• Key parameters such as contact angle and droplet mass were varied to observe effects on droplet dynamics and coalescence.

Main Results:

• The model qualitatively reproduced experimentally observed droplet coalescence behaviors on the virtual leaf surface.
• Varying the contact angle demonstrated that chemical defects can impede droplet movement and induce break-up.
• Substrate curvature gradients were identified as the dominant force driving the motion of typical spray-sized droplets.

Conclusions:

• Droplet movement on leaf surfaces is primarily governed by surface curvature gradients, especially for smaller droplets.
• Droplet coalescence increases mass, eventually making gravity the dominant force in droplet motion.
• The findings provide insights into optimizing agricultural spray application for enhanced retention and efficacy.