W. Richard Bowen and Nidal Hilal 4

5.3 MODIFICATION OF MEMBRANEs 161
Figure 5.18 shows the adhesion forces between initial and modified
PVDF membranes and the BSA-functionalised probe. At pH 3 and 5 the
initial PVDF membrane showed a higher adhesion than the modified
PVDF membrane. At the highest pH at which measurements were made,
the adhesion for the unmodified membrane was lower than for the modified
membranes, except for the membrane with the highest DM.
Effect of Ionic Strength The adhesion force measured between BSAcoated
colloid and modified PES membranes is shown in Figure 5.19. The
adhesion force for all the investigated membranes was found to increase
with increasing solution ionic strength. The modified membrane with
DM 367 �g cm �2 demonstrated the lowest adhesion force followed by the
initial membrane, which shows an increase in adhesion force compared
to modified membrane with medium DM.
Figure 5.20 shows the adhesion results for initial and grafted PVDF
membranes using BSA probes at different solution ionic strengths. An
increase in adhesion force with increasing ionic strength was observed
for both unmodified and modified membranes. Again a similar result to
PES membranes is noticed here where adhesion force has its lowest value
for modified PVDF with DM 346 �g cm �2 except at ionic strength of 1 mM
NaCl whereas grafted membrane with DM 530 �g cm �2 shows a slightly
lower adhesion than modified with DM 346 �g cm �2 .
Adhesion force (mN m –1 )
12
10
8
6
4
2
Initial PVDF
Modified PVDF DM = 224 μg cm –2
Modified PVDF DM = 348 μg cm –2
Modified PVDF DM = 530 μg cm –2
0
1 2 3 4 5
pH
6 7 8 9
fIgurE 5.18 Comparison of adhesion forces of BSA-modified probe to initial and
modified with qDMAEMA membranes in various pH solutions.