Environmental Engineering Reference
In-Depth Information
positive correlation is observed between surface energy and fouling load (
Table 4.4
,
r = 0.93), indicating that hydrophobic material gets fouled more than hydrophilic
material. A positive correlation is also observed between surface energy and TSS.
Adhesion of marine bacterial species on different surfaces have been investigated by
several researchers and they concluded that bacterial adhesion is less on low energy
surfaces and they are easier to clean because of weaker binding at the interface [22].
Kerr and Cowling [23] suggested that substrates with a surface energy between 5−25
mN/m will have minimum fouling. Baier and co-workers [24] and Baier [25] also
showed that there was a relationship between the surface energy and relative bacterial
adhesion. Similar indings were reported earlier by Sudhakar and co-workers [11].
Subsequent fouling of surfaces is governed by the initial conditioning ilm and not
by the initial surface energy of the substrates
.
A negative correlation (-0.73) was observed between surface roughness and TSS,
indicating that smooth surfaces attract more suspended solids. A negative correlation
was observed between surface energy and roughness in earlier ield studies with
LDPE, HDPE and PC [9, 14, 15] such a relationship with SR, PU, PET, SF, GFRP
and CFRP is not noticed.
4.5 Barnacles and their Cement
Barnacles are sessile creatures (
Figure 4.2
). They spend their entire lifetime attached
to a surface chosen during their cyprid larval stage. Generally, the attachment is an
irreversible process. The major challenge it faces is the environmental dynamics that
include intertidal current and winds and it has to overcome the possibility of being
swept away by the ocean waves. The adhesion happens because of the attachment
of its hard calcareous base plate to a ixed hard surface through a soft bio-organic
adhesive layer. The interface is a few microns thick and the variation in stiffness
changes quite drastically across the interface because of the presence of this adhesive
layer. Two major characteristics of barnacle adhesion are: a) its structural attributes
as a function of the different surfaces to which it attaches, and b) its biochemical
characteristics. Barnacle adhesive is capable of adapting itself based on the substrate
material to which it is attached to. These structures include surface roughness, texture,
wettability, modulus, thermal conductivity, stiffness, and chemical composition.
Adhesion studies have been reported on synthetic polymeric and metallic surfaces.
Adhesion on biological surfaces including other marine creatures has not been well
explored. It is known that marine creatures with textured surfaces suffer relatively
less barnacle attachment. Though barnacles are commonly found attached to mussel
shells (
Figure 4.2
), they can be easily peeled off which indicates a foul-release property
of the mussel [26].
