Drops on microstructured surfaces coated with hydrophilic polymers: Wenzel's model and beyond

Area of Science:

• Materials Science
• Surface Science
• Fluid Dynamics

Background:

• Understanding liquid behavior on textured surfaces is crucial for various applications.
• The Wenzel model describes how surface roughness affects wetting properties.
• Previous studies have explored wetting on rough surfaces, but precise meniscus motion remains complex.

Purpose of the Study:

• To investigate the wetting behavior of a polymer on micromachined silicon post surfaces.
• To quantitatively compare experimental contact angles with Wenzel's model predictions.
• To develop a model for liquid meniscus motion considering the specific post geometry.

Main Methods:

• Fabrication of micromachined silicon post surfaces.
• Coating surfaces with a polymer exhibiting a 70-degree contact angle on smooth material.
• Measurement of advancing and receding contact angles as a function of roughness.
• Comparison of experimental data with Wenzel's model.
• Development of a new model for meniscus motion.

Main Results:

• Drops were observed to wet the post surfaces in the Wenzel or 'penetration' mode.
• Advancing and receding angles were determined and analyzed in relation to roughness geometry.
• Discrepancies between experimental results and Wenzel's model were identified and discussed.

Conclusions:

• The study provides experimental data on wetting of polymer-coated posts, highlighting deviations from Wenzel's model.
• A novel model for meniscus motion is proposed, accounting for the liquid front's shape within the post structure.
• This research contributes to a more accurate understanding of liquid-surface interactions on complex microstructures.