Anisotropic drop spreading on superhydrophobic grates during drop impact

Area of Science:

• Fluid dynamics
• Surface science
• Materials science

Background:

• Understanding drop impact dynamics is crucial for various engineering applications.
• Microstructures significantly influence fluid behavior at the microscale.
• Anisotropic surfaces can lead to directional fluid spreading.

Purpose of the Study:

• To investigate the effect of geometric anisotropy in micro-grate structures on water drop spreading dynamics after impact.
• To elucidate the role of slip length in anisotropic drop spreading.
• To provide insights into controlling drop impact behavior using microstructured surfaces.

Main Methods:

• Experimental study of water drop impact on micro-grate structures with varying geometric anisotropy.
• Utilizing nanostructured grates to isolate the effects of slip length.
• Analysis of spreading dynamics using measurements of maximal spreading diameter.
• Development of a simplified energy balance model incorporating slip length.

Main Results:

• Maximal spreading diameter is larger parallel to grates than transverse beyond a critical Weber number.
• Asymmetric spreading increases with grate pitch and Weber number.
• Nanostructuring confirmed slip length as the primary factor for anisotropic spreading, excluding Cassie-to-Wenzel transitions and contact angle variations.
• Slip length selectively enhances spreading diameter parallel to grates.

Conclusions:

• Geometric anisotropy of micro-grate structures dictates asymmetric water drop spreading post-impact.
• Slip length is identified as the key mechanism driving this anisotropic spreading.
• The findings offer a pathway for designing microstructured surfaces to control drop dynamics in engineering applications.