1701039 (1 of 8)
2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Wetting State Transitions over Hierarchical Conical
Il Woong Park, Maria Fernandino, and Carlos A. Dorao*
contact angle, the contact angle hysteresis,
and the sliding angle. Cai et al.
the effect of the geometrical parameters of
the microstructures and side wall angle on
the wetting properties. In particular, it was
observed that the microstructures having a
side wall angle lower than 90° give higher
contact angle compared with the micro-
structures having side wall angle higher
The wetting phenomena in roughened
surfaces are normally referred to as the
Wenzel and Cassie–Baxter states.
Wenzel state describes a homogeneous
wetting regime where the liquid is con-
tacting with the surface, while the Cassie–Baxter state describes
a regime where an empty volume between a liquid droplet and
solid surface is observed. Several studies have been focused on
the transition between the Cassie–Baxter state and the Wenzel
state (Cassie–Wenzel transition)
and also the stability of
the Cassie wetting state.
However, which are the dominant
physical phenomena controlling each state and its transition
remains an open research issue. In particular, the transition
has been explained in terms of the threshold of the energy bar-
rier, meniscus touching on the substrate, air cushions beneath
the droplet, and critical pressure.
The control of the Cassie–Wenzel transition between supe-
rhydrophilic and superhydrophobic surfaces can contribute
to the design of surfaces with customized properties in a
diverse range of applications. At the same time, controlling the
Cassie–Wenzel transition can contribute to an improvement
of the understanding of the wetting states transition. For this
reason, experimental studies have attempted to gain control
of the Cassie–Wenzel wetting transition by an external excita-
tion such as vibration or electricity.
However, such active
control techniques of the Cassie–Wenzel wetting state can pre-
sent limitations in some applications. This fact has motivated
the need for controlling the Cassie–Wenzel wetting in a passive
manner by varying the geometrical parameters of the surface
without external excitations. Achieving a stable condition of the
Cassie–Wenzel state could be helpful for potential applications
The aim of this study is to fabricate surfaces presenting supe-
rhydrophobic and superhydrophilic states with a wide range
of geometric parameters. The selected surfaces are motivated
in conical structures observed in nature showing both super-
hydrophilic and superhydrophobic properties.
the Ruellia devosiana leaf shows impressive rapid spreading of
water and its leaves present a conical topography. The leaves of
the lotus ﬂower which have a hierarchical conical topography
Advancing in a better understanding of the physics of wetting requires to be
able to develop surfaces with well-controlled roughness by controlling the
microstructure morphology. In this study, patterned truncated cones and
hierarchical conical structures are fabricated. The wetting properties of the
fabricated surfaces are measured for identifying the importance of the geo-
metrical parameters on the wetting states ranging from superhydrophobic to
superhydrophilic. In particular, the wetting transition from Cassie–Baxter to
Wenzel state and its dependence on the geometrical parameters is investi-
gated. It is observed that the transition is dependent on the center-to-center
distance and the height of the structures.
I. W. Park, Prof. M. Fernandino, Prof. C. A. Dorao
Kolbjørn Hejes v1b
7491 Trondheim, Norway
The ORCID identiﬁcation number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/admi.201701039.
The wettability of a surface is a fundamental physical property
with relevance in many scientiﬁc and industrial applications.
It has been observed that many surfaces in nature exhibit supe-
rhydrophobic and superhydrophilic characteristics tailored to
some particular functionality.
The properties of such sur-
faces have motivated researchers mimicking them with the goal
of developing novel surfaces with customized properties.
However, major challenges have remained related to the fab-
rication techniques for achieving optimal controllability of the
properties of the surfaces which can also contribute to a better
understanding of the wetting phenomena.
Recent progress in fabrication techniques has allowed a
precise control of the surface properties in particular in terms
of shape and size for studying wetting phenomena.
example, Liu and Kim
fabricated a superhydrophobic surface
with a doubly re-entrant nano overhangs structure. This surface
has shown a high apparent contact angle even for liquids with
low surface tension. Chu and Nemoto
with micropillars and hierarchical structures showing a supe-
rhydrophobic state. In addition, a negative relation between
the apparent contact angle and the dynamic contact angle was
observed. Xue et al.
fabricated microcones by etching an
inclined surface with polystyrene array in order to study the
effect of geometrical parameters of microcones on the apparent
Adv. Mater. Interfaces 2018, 5, 1701039