A Simple Way To Achieve Pattern-Dependent Tunable Adhesion in Superhydrophobic Surfaces by a Femtosecond Laser

In this paper, we present a new approach to the tunable
adhesive
superhydrophobic surfaces consisting of periodic hydrophobic patterns
and superhydrophobic structures by femtosecond (fs) laser irradiation
on silicon. The surfaces are composed of periodic hydrophobic patterns
(triangle, circle, and rhombus) and superhydrophobic structures (dual-scale
spikes induced by a fs laser). Our results reveal that the adhesive
forces of as-prepared surfaces can be tuned by varying the area ratio
(ARs‑h) of superhydrophobic domain to hydrophobic
domain, thus resulting in tunable static and dynamic wettabilities.
By increasing ARs‑h, (i) the static wetting property,
which is characterized by the minimum water droplet volume that enables
a droplet to land on the surface, can be tailored from 1 μL
to 9 μL; (ii) the sliding angle can be flexibly adjusted, ranging
from >90° (a droplet cannot slide off when the sample is positioned
upside down) to 5°; and (iii) the droplet rebound behaviors can
be modulated from partial rebound to triple rebound. In addition,
the Cassie–Baxter model and the sliding angle model are used
to speculate the contact angles and sliding angles to provide potentially
theoretical models to design slippery-to-sticky superhydrophobic surfaces.
The tunable adhesive superhydrophobic surfaces achieved by fs laser
microfabrication may be potentially used in microfluidic systems to
modulate the mobility of liquid droplets.