Contact Angle Measurements over Macro, Micro and Nano Dimensioned Systems - Drops and Bubbles in Contact with Solid Surfaces - page 2

Figure 1. Static Cantact Angle: 1 mm diameter water drop on a polymer solid substrate.
basic formula to manage common industrial wetting problems where, at least from
a qualitative and macroscopic point of view, it is quite useful to deduce an idea of
the behavior of the evaluated liquid-solid system by taking some pictures of the
profile of a static drop. Therefore, by observing the results provided on a macro-
scopic scale by this visual approach, originated with the Ramé-Hart goniometric
technique and arriving at very precise modern tensiometer systems, wetting science
seems to be an easy piece. While this simple point of view was rather accepted
till some years ago the introduction of micro and nanotechnologies made it now
difficult to be supported even for first sight industrial applications.
B. History
The deep complexity features of wetting problems arose at general attention in the
mid sixties of the last century after the fundamental work done by Zisman [2] that
followed other papers published with Fox [3], Ellison [4], Shafrin [5] and Bernett
[6]. Later on in the eighties De Gennes, who established another milestone with
his review [7] about the state of the art of wetting science, Brochard-Wyart, Caz-
abat and co-authors studied [8-13] the influence of long range forces, spreading
phenomena and rough substrates, while Neumann working with Good, Kwok and
others, moved toward the definition of the Equation of State Approach (ESA) [14,
15] following a path that may be appreciated in [16].
During the nineties till to the present days the studies concerning wetting prob-
lems became further specialized in their topics, according to a sensible evolution
of the available experimental techniques. This fact determined a consequent im-
provement of the theoretical basis upon which wetting studies may rely, as it may
be appreciated in the following authors that, as well as many co-authors and those
who treated micro and nano wetting issues, have produced an impressive amount
of papers impossible to be mentioned. Their citation here has therefore to be in-
tended only as a mere guide and not as an exhaustive panorama of their activity
or of the available literature. The spreading phenomena on a micro dimensioned
solid-liquid system were evaluated for example by Gu et al. [17, 18], Erickson et
al. [19], De Coninck et al. [20, 21], Blake et al. [22-24], De Ruijter et al. [25],
Voue' et al. [26], Shanahan [27, 28], Starov et al. [29, 30], Lee et al. [31], Wasan et