W. Richard Bowen and Nidal Hilal 4

146 5. AFM AND DEvELOPMENT OF (BIO)FOULINg-REsIsTANT MEMBRANEs
25 µm
12.5 µm 12.5 µm
0 µm Z scale = 720 nm
(a) (c)
12.5 µm
25 µm
12.5 µm
although both are characterised by the same nominal pore size. The surface
of grafted membrane having the lowest DM (shortest polymer chain length)
appeared to have a laterally inhomogeneous structure consisting of clusters.
As the DM increased (leading to an increased graft chain length), the clusters
became higher and the grafted chain gathered into larger clusters.
Membrane Surface Analysis
From AFM images, surface analysis was carried out using instrument
software to obtain surface roughness parameters. The formation of
the graft polymer layer on the membrane surface resulted in significant
changes in surface morphology. Structural modifications become more
pronounced with increasing DM. Figure 5.4 and Tables 5.1 and 5.2 present
quantitative characteristics of the surface morphology of the initial
and modified membranes derived from the AFM images [20].
The same trend can be observed in the roughness values for both
PES and PVDF membranes. A slight increase in the membrane roughness
compared with the unmodified membrane was observed for membranes
modified with the lowest degree of grafted polymer (202 �g cm �2 ).
At such a DM, grafted chains could be accommodated within the pores.
Further increases in DM led to a significant increase in surface roughness
with a layer of grafted polymer forming its own porous structure.
0 µm
25 µm
Z scale = 720 nm
25 µm
0 µm Z scale = 720 nm 0 µm Z scale = 720 nm
(b) (d)
fIgurE 5.4 High-resolution 3D AFM images of initial (a) and modified with
qDMAEMA (b)–(d) PES membranes; (b) DM � 202 �g cm �2 , (c) DM � 367 �g cm �2 and (d)
DM � 510 �g cm �2 .