Biomedical Engineering Reference
In-Depth Information
Contact Angle Measurements over Macro, Micro and Nano
Dimensioned Systems
Fabrizio Barberis
Department of Civil, Environmental and Architectural Engineering, Materials Engineering Section,
Faculty of Engineering, University of Genoa, Piazzale J.F. Kennedy 1, Pad D, 16129, Genoa, Italy.
E-mail: fabrizio.barberis@unige.it
Contents
A.Science .................................................
1
B.History..................................................
2
C. Young Equation and True Equilibrium
. . ..............................
3
D.TheEquationofStateApproach....................................
5
E.TheAcid-BaseApproach .......................................
7
F.ExperimentalApplication .......................................
9
G. Equilibrium and Adsorbed Films
...................................
13
H.MicroscopicandNanoscopicContactAngles ............................
19
I.Conclusions...............................................
25
J.References................................................
25
A. Wetting Science
Wetting science, in its more classical definition, studies the way of interaction of
a fluid with a solid surface, which determines the specific shape that liquids as-
sume when they are deposited on a solid substrate. T. Young in 1805 [1] stated that
a liquid drop placed on a solid surface assumes a geometrical shape that can be
described by his famous formula (1), that became the milestone of wetting studies:
cos
θ
γ
sl
)/γ
lv
,
(1)
where
θ
is the static contact angle,
γ
sv
and
γ
sl
are the solid-vapor and solid-liquid
surface energies and
γ
lv
is the liquid surface tension (Fig. 1). The
Young Equation
(YE) therefore describes how, in a true equilibrium condition, the contact angle
between a fluid and a solid depends only upon the intrinsic nature of the mate-
rials engaged in the wetting experience. No dimension or gravity constraints are
apparently present in it. Due to its apparent simplicity YE is still considered as the
=
(γ
sv
−
