W. Richard Bowen and Nidal Hilal 4

The antibacterial activity of initial unmodified (PES and PVDF) membranes
as well as membranes modified with qDMAEMA polycations
were evaluated against E. coli bacteria. After incubation with viable E. coli
bacterial cells on each membrane, the growths of bacterial plaques were
compared. Figure 5.3 shows PES membranes of which one is modified by
incubation with 367 �g cm �2 qDMAEMA. The results showed that membrane
samples with grafted qDMAEMA as well as ones modified with PEI
possess a strong antimicrobial action towards E.coli bacteria.
This antimicrobial activity was found to be independent with relation
to the degree of modification (DM) of the membrane. The modified membranes
possessing biocide properties could be potentially more resistant
to (bio)fouling in water treatment applications.
5.3.2 Membrane Characterisation
5.3 MODIFICATION OF MEMBRANEs 145
Membrane Surface Morphology
Membrane surface topography and conformational changes due
to modification were examined using AFM in contact mode. All AFM
images were made in air at room temperature. Figure 5.4 presents 3D
AFM images of initial PES membranes and modified membranes with
different degrees of polymer grafting [8, 20].
It can be seen that surface topography is markedly different in texture
for unmodified membranes compared with the modified membranes,
(a) (b)
fIgurE 5.3 Viability of E.coli cells on the surface of initial PES (a) and modified
with qDMAEMA membranes, DM � 367 �g cm �2 (b). Five millilitres of E. coli suspension
(15 E. coli per ml) were filtered through both membranes.