Marine Biofouling of Polymers - Polymers in a Marine Environment - page 62

block copolymers of poly[poly(ethylene glycol)methyl ether methacrylate]- block -
poly(2,3,4,5,6-pentaluorostyrene) (P(PEGMA)- b -PPFS). The amphiphilic copolymer
has the typical luoropolymer characteristics including low surface energy, high
chemical and thermal resistance and self-assembly behaviour and the P(PEGMA)
characteristics including water afinity, low toxicity, high biocompatibility and foul
resistance to proteins. The nanoscale patterns on the copolymer surface and its ability
to reorganise itself in water discourages the settlement of barnacles.
Another coating that combines the advantages of both silicones and amphiphilic
luoropolymers was produced by Martinelli and co-workers [96]. This diblock
copolymer consisted of a linear polysiloxane block and an amphiphilic PEGylated-
luoroalkyl modiied PS block with a degree of polymerisation ranging from 6 to 12.
The coatings were obtained by dissolving the two block copolymers in a PDMS matrix.
This diblock copolymer was capable of imparting both low elastic modulus and low
surface energy properties. All the coatings showed excellent foul-release properties
against Ulva , with 3- to 14-fold improvement in the release of Ulva sporelings when
compared to PDMS. The adhesion strength was signiicantly reduced at the higher
concentration of block copolymer in the blend.
Surfaces coated with quaternary ammonium salt (QAS)-containing polymers are
very effective at killing a wide range of gram positive and gram negative bacteria,
yeast and moulds. These surfaces have a high positive charge density that helps in
the strong electrostatic interaction with negatively charged bacteria. Adsorption of
QAS on the bacterial cell wall leads to its diffusion through the wall and disrupts the
cytoplasmic membrane of the cell. This releases potassium and other components
that cause cell death [97].
The alkyl chain length of QAS plays an important role in the antimicrobial activity.
Tiller and co-workers [98] reported that propylated, butylated, hexylated and
octylated immobilised poly(4-vinyl- N -alkylpyridinium bromide) chains are effective
in reducing the bacterial cell viability. No activity was observed with alkyl chains
of length C 8 −C 16 . These chemically bound 'tethered' groups possibly interact with
each other through hydrophobic forces between alkyl moieties, and electrostatic
repulsion between cationic groups. Thus, these studies show that by optimising the
chain length of alkyl groups, a balance between these two forces is created which is
useful in reducing bacterial viability.
Majumdar and co-workers [88] carried out a high throughput assay to develop
structure - antimicrobial activity relationships for polysiloxane coatings containing
tethered QAS moieties. A blend of a silanol-terminated PDMS (HO-PDMS-OH),
a QAS-functional alkoxysilane, and the crosslinker, methyltriacetoxysilane was
synthesised as a QAS-based coating. QAS concentration and polysiloxane MW played