BULETINUL INSTITUTULUI POLITEHNIC DIN IAŞI - Universitatea ...

108 Birgit Kjærside Storm
They are not able to cover each other and the materials behind them are not able
to wet each other.
Fig. 2 – Two spheres in a HSP diagram.
The two spheres are not touching each other. The two materials behind are not compatible.
If wetting of a material with another material shall be possible, the solubility
spheres for the two materials shall at least touch each other. To calculate if
wetting of a material with another material for example an adhesive is possible
the RED – relative energy density – value can be calculated. The RED value is
defined as:
(3) RED = Ra/R0,
Ra is the distance between the centre of the two spheres and R0 is the centre of
the material, which shall be compared with the other sphere. If the RED number
is 1, there is no compatibility/solubility between the two
compared materials.
As mentioned above the surface tension, γ, can be measured or be calculated
from the HSP. Different researchers have found the correlation between the
surface tension and the HSP. The most used is
(4) γ = 0,0688V 1/3 [δD 2 + k (δP 2 + δH 2 )]
γ is the surface tension and k is constant depending on the liquids involved.
Other similar correlations are used.