W. Richard Bowen and Nidal Hilal 4

4.2 THE RANgE OF POssIbILITIEs FOR INvEsTIgATINg MEMbRANEs 109
studies for membrane technology. Some more advanced topics will then
be considered: the correspondence between surface pore dimensions
from AFM and MWCO (molecular weight cut-off); imaging in liquid
and the determination of surface electrical properties; effects of surface
roughness on interactions with particles; ‘visualisation’ of the rejection
of a colloid by a membrane pore and the use of AFM measurements in
membrane development. The written text and technical details will be
kept to a minimum throughout. Such details are described fully in the
original publications. The intention is to let the images ‘speak’ for themselves!
The second intention is to provide a short account of AFM studies
of metal surfaces, especially stainless steel surfaces. Stainless steel is
extensively used in the construction of membrane equipment, and the
interaction of process streams with its surface can be a significant factor
in the overall successful operation of the separation process. Such studies
also have broader relevance due to the widespread use of stainless steel
in many process industries.
4.2 ThE RAngE OF POSSIbILITIES FOR
InVESTIgATIng MEMbRAnES
A membrane technologist acquiring an Atomic Force Microscope for
the first time is best advised to begin with relatively simple measurements.
A good starting point is to image some track-etch membranes in
air. The pores in such membranes may also be imaged using a good optical
microscope, which gives assurance about the images produced by
AFM. As an example, Figure 4.1 shows an AFM image of a Cyclopore
membrane of specified pore dimensions of 0.2 �m [1].
µm
0.20
0.10
0.00
3
µm
2
1
0
0
1
µm
2
3
% of pores
25
20
15
10
5
0
0.10 0.15 0.20 0.25 0.30 0.35
Pore size, µm
FIgURE 4.1 AFM image and pore size distribution of Cyclopore membrane.