Drops on the Underside of a Slightly Inclined Wet Substrate Move Too Fast to Grow

Area of Science:

• Fluid dynamics
• Surface science
• Physics of liquids

Background:

• Pendant drops on wet substrates typically grow by accumulating surrounding fluid, leading to dripping.
• Drop translation on a horizontal film accelerates fluid accumulation and growth.

Purpose of the Study:

• To investigate the effect of substrate inclination on pendant drop dynamics.
• To identify and rationalize a novel drop decay regime.
• To predict the transition between drop growth and decay.

Main Methods:

• Experimental observation of drop behavior on tilted substrates.
• Numerical simulations of fluid flow and drop evolution.
• Analytical treatment of the Landau-Levich meniscus.

Main Results:

• Slight substrate tilting (≈2°) reverses conventional drop growth, causing decay.
• A critical inclination angle governs the transition between growth and decay regimes.
• Quantitative predictions for drop dynamics in both regimes were developed.

Conclusions:

• Substrate inclination is a critical factor controlling pendant drop size.
• A new understanding of fluid dynamics at tilted interfaces is established.
• The findings offer insights into phenomena like condensation and coating processes.