Contact angle hysteresis on superhydrophobic stripes.

Area of Science:

• Surface Science
• Wettability Studies
• Superhydrophobic Materials

Background:

• Contact angle hysteresis is crucial for droplet manipulation on surfaces.
• Superhydrophobic surfaces with patterned textures offer tunable wetting properties.
• Understanding the influence of surface topography on contact angle hysteresis is essential.

Purpose of the Study:

• To experimentally and quantitatively investigate contact angle hysteresis on striped superhydrophobic surfaces.
• To determine the effect of solid fraction (ϕS) on receding and advancing contact angles.
• To develop a theoretical model explaining the observed wetting behaviors.

Main Methods:

• Experimental measurements of contact angle hysteresis on striped superhydrophobic surfaces with varying solid fractions.
• Quantitative analysis of receding and advancing contact angle regimes.
• Development of a theoretical model incorporating surface defects and elastic energy.

Main Results:

• Receding contact angle was found to be isotropic, with its cosine growing nonlinearly with solid fraction.
• Advancing contact angle was anisotropic (except in dilute regimes) and dependent on droplet rolling motion.
• A generalized Cassie equation and a model for strong defect energy were developed to explain results.

Conclusions:

• Receding angles are governed by longitudinal sliding, while advancing angles depend on texture anisotropy and droplet adhesion.
• The theoretical model accurately describes the influence of surface defects and elastic energy on contact angle hysteresis.
• Contact angle hysteresis is generally anisotropic but becomes isotropic at low solid fractions (ϕS ≤ 0.2).