Contact angle hysteresis on textured surfaces with nanowire clusters

Area of Science:

• Materials Science
• Surface Science
• Nanotechnology

Background:

• Nanowire arrays are crucial for various applications, but their fabrication often results in agglomeration.
• Controlling nanowire morphology impacts surface properties like hydrophobicity and wetting behavior.

Purpose of the Study:

• To investigate the effect of different drying methods on the morphology and wetting properties of copper nanowire (CuNW) arrays.
• To understand the relationship between nanowire arrangement, surface topography, and contact angle hysteresis.

Main Methods:

• Fabrication of CuNW arrays (200 nm diameter, 2-25 µm length) using anodic aluminum oxide (AAO) templates.
• Application of different drying treatments: thermal, evaporative, and supercritical drying.
• Characterization of nanowire morphology and measurement of contact angle hysteresis.
• Analysis of wetted solid fraction using the Cassie-Baxter model.

Main Results:

• Thermal and evaporative drying led to CuNW agglomeration due to surface tension.
• Supercritical drying yielded well-defined, bundled-free, vertically-standing CuNW arrays.
• All surfaces exhibited hydrophobicity, but surfaces with bundled nanowires showed larger contact angle hysteresis.
• Wetted solid fraction analysis correlated hysteresis with liquid/solid contact area on textured surfaces.

Conclusions:

• Supercritical drying is a superior method for fabricating vertically aligned, non-agglomerated CuNW arrays.
• Nanowire bundling significantly influences contact angle hysteresis, with bundled structures exhibiting higher hysteresis.
• The Cassie-Baxter model effectively explains the contribution of surface texture and wetted fraction to wetting behavior.