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. 2025 Jan 2;10(1):20.
doi: 10.3390/biomimetics10010020.

Tuning Wetting Properties Through Surface Geometry in the Cassie-Baxter State

Talya Scheff  1 , Florence Acha  1 , Nathalia Diaz Armas  1 , Joey L Mead  1 , Jinde Zhang  1
Affiliations

Tuning Wetting Properties Through Surface Geometry in the Cassie-Baxter State

Talya Scheff et al. Biomimetics (Basel). .

Abstract

Superhydrophobic coatings are beneficial for applications like self-cleaning, anti-corrosion, and drag reduction. In this study, we investigated the impact of surface geometry on the static, dynamic, and sliding contact angles in the Cassie-Baxter state. We used fluoro-silane-treated silicon micro-post patterns fabricated via lithography as model surfaces. By varying the solid fraction (ϕs), edge-to-edge spacing (L), and the shape and arrangement of the micro-posts, we examined how these geometric factors influence wetting behavior. Our results show that the solid fraction is the key factor affecting both dynamic and sliding angles, while changes in shape and arrangement had minimal impact. The Cassie-Baxter model accurately predicted receding angles but struggled to predict advancing angles. These insights can guide the development of coatings with enhanced superhydrophobic properties, tailored to achieve higher contact angles and customized for different environmental conditions.

Keywords: Cassie–Baxter state; contact angle hysteresis (CAH); dynamic wetting; photolithography; silicon micro-posts; superhydrophobicity; surface geometry.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Fabrication processes for all silicon wafers.
Figure 2
Figure 2
Tensiometer reading of advancing contact angle.
Figure 3
Figure 3
Tensiometer reading of receding contact angle.
Figure 4
Figure 4
(Left) Test Phase and (Right) Experimental Phase.
Figure 5
Figure 5
Samples with varied hard bake temperature and times.
Figure 6
Figure 6
Graph used to determine optimal ICP etch time.
Figure 7
Figure 7
(Left) Undercut sample and (Right) optimal 5.0 sccm sample.
Figure 8
Figure 8
The effect of solid fraction on static and dynamic contact angle.
Figure 9
Figure 9
Comparing experimental dynamic angles to theoretical values predicted by Cassie–Baxter equation.
Figure 10
Figure 10
Contact angle hysteresis (CAH) compared to sliding angle.
Figure 11
Figure 11
Comparing the sin of the sliding angle with the cos of the receding angles minus the cos of the advancing angle.
Figure 12
Figure 12
Comparing static and dynamic angles when edge-to-edge spacing is changed.
Figure 13
Figure 13
Comparing static and dynamic angles when shape and arrangement is changed.
See this image and copyright information in PMC

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