W. Richard Bowen and Nidal Hilal 4

164 5. AFM AND DEvELOPMENT OF (BIO)FOULINg-REsIsTANT MEMBRANEs
300
(a)
Å
2.00
1.00
0.00
200
Å
100
0 0
100
Å
200
300
Å
4.00
3.00
2.00
1.00
0.00
200
Å
100 100
due to increase in the surface porosity. Changes in the thickness and/or
the structure of the porous layer of the membrane may account for this.
Force measurements were also carried out between �4-�m silica
spheres and membranes. Figure 5.22 shows examples of typical data for
force measurements taken from polysulphone membranes, with and without
SPEEK present in 0.01 M NaCl. For the non-SPEEK membrane (P-P) the
colloid probe snaps-in to the membrane surface, which indicates the presence
of long-range attractive forces, sufficient in magnitude to overcome
the restoring force on the cantilever. This type of attraction leads to fouling
300
0 0
fIgurE 5.21 AFM images of polysulphone membranes obtained with contact mode in
air. (a) Polysulphone membrane and (b) polysulphone/SPEEK membrane (5% SPEEK prepared
at 20°C). Roughness values were obtained from 2 � 2 �m images.
tAblE 5.6 summary of AFM Characterisation Data for sPEEK Modified
Polysulfone Membranes.
(b)
P-P S0.5-20 S2-20 S5-20 S2-10 S2-60
r p (nm) 0.93 � 0.15 0.89 � 0.22 0.93 � 0.15 0.73 � 0.18 1.05 � 0.22 0.86 � 0.26
rms roughness
(nm)
3.2 4.2 3.5 2.5 3.1 2.1
Porosity, e (%) 6.0 9.0 14.1 16.9 15.1 12.8
Snap-in events
(out of 9)
F off, F/R
(mN/m)
9 4 3 0 1 4
28.5 � 4.3 10.0 � 14.8 3.9 � 1.6 0.75 � 2.7 � 2.8 9.6 � 5.3
Å
200
300