Dynamic Drop Penetration of Horizontally Oriented Fiber Arrays.

Area of Science:

• Fluid Dynamics
• Materials Science
• Biophysics

Background:

• Mammalian fur coats provide natural water resistance.
• Understanding liquid-solid interactions in fibrous structures is crucial for designing protective materials.

Purpose of the Study:

• To investigate the dynamics of drop impact on fiber arrays.
• To determine how fiber properties influence liquid penetration and spreading.
• To explore the potential of fiber arrays as rain barriers.

Main Methods:

• Experimental study of drop impact on 3D-printed fiber arrays.
• Systematic variation of packing density, fiber alignment, cross-section, and wettability.
• Image analysis to quantify penetration depth and wetted width.

Main Results:

• Drop penetration is governed by impact Weber number and array porosity.
• Staggered fibers significantly reduce penetration, especially hydrophobic ones.
• Increased fiber density leads to penetration independent of impact velocity, forming a rain barrier.
• Hydrophilicity promotes lateral spreading and inhibits fragmentation, enhancing resistance to dynamic penetration.

Conclusions:

• Fiber arrays can function as effective rain barriers, with density being a key factor.
• Wettability influences penetration dynamics, with hydrophilic fibers resisting dynamic impact and hydrophobic fibers resisting wicking.
• Drop mass penetration becomes independent of wettability above a critical Weber number.