W. Richard Bowen and Nidal Hilal 4

5.3 MODIFICATION OF MEMBRANEs 149
Before detailed discussion of the quantitative characteristics of surface
morphology, it is worth noting that the chosen lognormal pattern for
PDS described by equation (5.1) gave a correlation coefficient of at least
0.95 for all fitted curves. The most probable pore sizes estimated from
fitted curves were very close to the mean pore diameter calculated from
corresponding sets of pore sizes for the initial and modified membranes
(Tables 5.4 and 5.5).
According to Figure 5.5(a), the initial PES membrane has a very wide
PSD with a � value of 0.56 �m. However, grafting of poly-qDMAEMA
resulted in narrowing of the PSD and shifting the whole curve towards
smaller pore sizes. As a result, mean pore size is gradually decreasing
with the increase in the amount of poly-qDMAEMA grafted to the membrane
surface. Significant improvement of the PSD was observed even
for the modified PES membranes with the smallest DM (Table 5.4).
Narrowing of the PSD occurred mostly due to the disappearance of
large pores (larger than 0.6 �m). Taking into consideration that substantial
narrowing of large pores demands higher quantities of grafted polymer
tAblE 5.4 AFM Measurements of Pore size and PsD of Initial and
Modified PEs Membranes with qDMAEMA.
Mean pore PSD parameters
DM (�g/cm 2 ) size (�m) X 0 (�m) %f max �
0 0.470 � 0.188 0.353 � 0.028 19.8 � 2.2 0.56 � 0.08
202 0.337 � 0.098 0.278 � 0.010 41.4 � 4.4 0.32 � 0.04
367 0.293 � 0.072 0.281 � 0.003 51.3 � 2.0 0.26 � 0.01
510 0.100 � 0.083 0.075 � 0.004 26.9 � 2.9 0.40 � 0.05
tAblE 5.5 AFM Measurements of Pore size and PsD of Initial
and Modified PvDF Membranes with qDMAEMA.
Mean pore PSD parameters
DM (�g/cm 2 ) size (�m) X 0 (�m) %f max �
0 0.535 � 0.082 0.555 � 0.003 51.2 � 1.7 0.14 � 0.01
224 0.445 � 0.083 0.439 � 0.018 35.1 � 4.1 0.28 � 0.02
346 0.334 � 0.079 0.297 � 0.013 44.3 � 5.7 0.30 � 0.01