Environmental Engineering Reference
In-Depth Information
This explains why siloxane-based elastomers with both a low surface energy and low
E show very low bioadhesion.
2.4.1.3 The Correlation of Polymer Structure and Bioadhesion
By comparing the properties of hydrocarbon, luorinate and silicone polymers, one
can conclude that the chemical structure of polymers inluences biofouling (
Table 2.2
).
The backbone bond energy of siloxane is 30% stronger than that of hydrocarbon
polymers. The backbone bond angle of siloxane is also larger than that of hydrocarbon
polymers. The activation energy for rotation about the (-Si-O)
n
backbone is zero.
This makes siloxane polymers very mobile and gives them a restructuring ability
[9, 45]. This makes them more resistant to biofouling when compared to hydrocarbon
polymers. For luorinated polymers the bond energy with carbon is 24% greater than
with hydrocarbons, 540 kJ/mol and 435 kJ/mol, respectively. Because the covalent
radius of luorine is twice that of hydrogen and the luorine atoms are also large,
a PE polymer assumes a fully eclipsed conformation whereas PTFE does not [45].
Table 2.2 Comparative properties of hydrocarbons, silicone and luorine
Properties
Hydrocarbon
Silicone
Fluorine
Backbone bond length C-C /Si-O/ F-O (°A)
1.54
1.65
1.54
Backbone bond angle
112°
159°
112°
Effective van-der-Waals radius (°A)
1.2
2.0
1.35
Activation energy (Eact) of backbone rotation (J/mol)
13.8
0
19.7
Krishnan and co-workers [49] reported that amphiphilic surfaces have the ability
to undergo an environment dependent surface transformation when in contact with
the extracellular polymeric substances making them less vulnerable to bioadhesion.
2.4.1.4 Electrostatic Interactions and Adhesion
Physical properties such as charge are also important for adhesion. Most bacteria
carry a negative charge on their surface. Fletcher and Loeb [40] investigated the
attachment of
Pseudomonas sp
., to a variety of surfaces. They observed that large
numbers of bacteria attached to hydrophobic plastics such as Telon, PE, PS and
