Environmental Engineering Reference
In-Depth Information
PET which had little or no surface charge, but that very few bacteria attached to
hydrophilic, negatively charged substrata such as glass, mica, or oxidised plastics.
Rosenhahn and co-workers [1] showed that electrostatic interactions directly inluence
adhesion of
Ulva
spores on surfaces. They themselves carry a negative surface energy
of 19 mV. The strength of adhesion and the number of spores is dependent on the
density and sign of the charge of PTFE surfaces. Negatively charged PTFE surfaces
showed a reduction in the settlement of
Ulva
when compared to uncharged or
positively charged PTFE surfaces.
2.4.1.5 Surface Roughness and Topology
Surface topological features contribute to the attachment of the organisms to surfaces.
It has been observed that bacteria preferentially attach to rough surfaces. There are
three hypotheses for this:
(i) There is a higher surface area offered for attachment,
(ii) They are protected from shear forces, and
(iii) There are chemical changes, which favour physicochemical interactions [50].
In marine biofouling, topology has been shown to alter the settlement of bacteria,
barnacles, and algae. The change in surface wettability because of surface roughness
could be the contributing factors to these responses. A negative correlation is observed
between surface energy and surface roughness of polymers. Kerr and Cowling [51]
suggested that surfaces with a root mean square roughness of 5-25 nm will have
minimum fouling. Many studies have shown that as roughness increases, the contact
angle increases and that, in turn, increases the γ
c
[9]. The presence of grooves has a
signiicant effect on the rate of adhesion of cells, with preferential attachment on the
downstream edges. This has been attributed to the accumulation of charge on abrupt
edges or discontinuous surfaces [50].
2.4.1.6 Thickness
The thickness of foul release polymers used is an important factor that affects
the adhesion of fouling organism. This is because less force is needed to dislodge
the organism from a thicker coating and the thickness of the coating allows the
coating modulus to be controlled [50, 51]. The thickness of silicone polymer and
luoropolymer coatings are 150 µm and 75 µm, respectively [52]. The importance of
the thickness of polymer coating in fouling organism release is given by Kendall's [53]
