BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI - Universitatea ...

Bul. Inst. Polit. Iaşi, t. LVI (LX), f. 2, 2010 107
of a surface and the determination of the surface tension by the droplet method
is sketched. The surface tension of as well the metal/anodized metal and the
adhesives depends on the secondary bonding forces in the material. For
aluminium and anodized aluminium the surface will react with CO2. This
reaction causes a low surface tension of the surface, which gives a bad wetting
with the adhesive.
The surface tension can be measured or it can be calculated from knowledge
about the solubility parameters. The solubility parameters can be measured
indirectly or they can be calculated.
Fig. 1 – Surface tension and determination of surface tension [5].
The solubility parameters can be a one-dimensional parameter or a three
dimensional parameter. The solubility parameter is defined as
(1) δtot 2 = ∆Evap/Vl,
δtot is the total is the total solubility, ∆Evap the heat evaporation and Vl is the
molar volume.
The one dimensional solubility parameter gives not the total answer for the
secondary bonding forces. Therefore Charles Hansen defined the Hansen
Solubility Parameters, HSP, which are three dimensional solubility parameters.
(2) δtot 2 = δd 2 + δp 2 + δh 2 ,
δd is the contribution from the dispersion forces, δp is the contribution from the
polar forces and δh is the contribution from the hydrogen forces.
The three contributions will be put into a three dimensional coordinate
system, where the dispersion forces will be printed with the double value of the
two others. Each material, chemical or solvent will besides a three dimensional
solubility parameter, which will be the centre in a sphere, also have an action
radius, R0. The action radius is the area around the centre where the
material/chemical is able to be dissolve or in other way to interact with other
materials. The HSP can be set up in a three dimensional diagram and the
wetting possibility can in that way directly be observed by studying if there are
overlap by the spheres. In Fig. 2, two spheres are set up besides each other.