Scientists develop simple model to predict drop behavior on surfaces

Researchers, led by Hans-Jürgen Butt from the Max Planck Institute for Polymer Research, have made strides in understanding how drops interact with surfaces. These interactions play a role in various everyday applications like inkjet printing, solar cells, eyeglasses, and cameras.

In the realm of inkjet printing, drops must stay in place for precise prints, while solar cells and optical surfaces benefit from drops rolling off quickly, carrying dirt away. Predicting drop behavior is complex due to microscopic surface properties. Water-repellent surfaces result in spherical drops with minimal friction, allowing them to roll off even on slight inclines. Water-attracting surfaces create flat drops that need steeper angles to move.

To address this challenge, researchers examined drop behavior on inert, smooth surfaces. They measured flowing drop velocity, dimensions, and liquid-solid surface angles. By studying liquids like water, glycerin, and silicone oil on materials like silicon, glass, and Teflon, they established correlations. They found that drop friction can be described by a single dimensionless parameter when combined with viscosity.

Xiaomei Li, a doctoral student involved, noted the surprising simplicity in describing rolling drops. Rüdiger Berger, a group leader, highlighted the newfound fascination with drops in daily life.

Numerical simulations showed that friction mostly occurs along the drop’s edge to the surface. The research aims to predict drop behavior accurately, aiding surface selection for various applications. The findings were published in Nature Communications.

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