1 research outputs found
Study of Transitions between Wetting States on Microcavity Arrays by Optical Transmission Microscopy
In this article, we present a simple
and fast optical method based
on transmission microscopy to study the stochastic wetting transitions
on micro- and nanostructured polymer surfaces immersed in water. We
analyze the influence of immersion time and the liquid pressure on
the degree of water intrusion in individual microcavities on these
surfaces as well as the lifespan of their superhydrophobicity. We
show that transitions among the three wetting states (Cassie, Cassie-impregnating,
and Wenzel) occur with a certain pressure threshold (300 mbar for
a microcavity diameter of 7.5 ÎĽm). Below this threshold, the
transitions between the Cassie and the Cassie-impregnating states
are reversible, whereas above this threshold, irreversible transitions
to the Wenzel state start to occur. The transitions between the different
wetting states can be explained by taking into account both the Young–Laplace
equation for the water menisci in the cavities and the diffusion of
dissolved gas molecules in the water. In addition, the wetting transitions
had a stochastic nature, which resulted from the short diffusion distance
for dissolved gas molecules in the water between neighboring cavities.
Furthermore, we compared the contact angle properties of two polymeric
materials (COC and PP) with moderate hydrophobicity. We attributed
the difference in the water repellency of the two materials to a difference
in the wetting of their nanostructures. Our experimental observations
thus indicate that both the diffusion of gas molecules in water and
the wetting properties of nanostructures are important for understanding
the sustainability of superhydrophobicity of surfaces under water
and for improving the structural design of superhydrophobic surfaces