Contact Angle Measurements over Macro, Micro and Nano Dimensioned Systems - Drops and Bubbles in Contact with Solid Surfaces - page 13

Figure 7. Wetting vs. pseudo-partial.

due to spreading events and is quite common when, for example, wetting problems
concerning viscous fluids like oils or glycerol are studied.
The Coefficient of Spreading sounds like (16)
S

γ sl (16)
and takes into account, on a thermodynamic basis, the chance of a fluid to move
simply due to energetic difference between itself and the surrounding materials.
On a practical ground it can be therefore highlighted that these effects create an
energetic metastable condition that, on a microscopic scale, provides at least two
problems to be dealt with:
(a) An effective achievement of True Equilibrium conditions .

= γ sv − γ lv −

(b) A wise discrimination among Multiple contact angles collection.

G. Equilibrium and Adsorbed Films
A problem that gained an exceptional importance in the last years shows up when
the chemical equilibrium is affected by liquid-solid or even liquid-atmospheric
fluid interactions.
The lack of chemical equilibrium, originally intended as a 'simple' condition by
which bulk phases involved in the experiments were allowed to exchange molecules
between their interfaces, was usually intended as an important but not fundamental
boundary condition of massive wetting issues. Recently indeed this problem be-
came The Problem since researchers focused their attention at dimensions at which
interfaces are thewholesystem , i.e., micro and nanowetting issues. The full impor-
tance of liquid and solid surface contaminations, beneath evident in its importance
to those who normally deal with chemi or physi-sorption tasks [186], is not equally
stressed by most of those who, time to time, deal with wetting issues. Figure 8 re-
ports the diagram of surface tension variation of high purity water when exposed
to normal laboratory atmosphere in which no known air pollutants as solvents or