Nodules/nodular aggregates

Table 4.15 summarizes the applications, pore sizes, nodule/nodular aggregate sizes, and roughness (surface) parameters for different polymeric membranes that are covered in this chapter. The following conclusions can be drawn from this table ... 

Table 4.15. A summary of application, pore sizes, nodule/nodular aggregate sizes, and roughness... 

Important membrane surface properties include the size of nodules and nodule aggregates, the shape of pores, the pore size and pore size distribution, and the surface roughness. In this chapter, the focus will be on nodules and nodular aggregates since AFM seems most suitable for those. Moreover, there is evidence that nodular structure has some relationship to membrane performance. 

Nodular aggregates—spherical clumps of nodules, from 400 to 1000 A in diameter... 

As discussed, the cross-sectional view of the membranes observed by AFM has similar characteristics to those observed by high-resolution FE-SEM, confirming that AFM can be used to study the cross-sectional structure of polymeric membranes, particularly in terms of their nodular structures. The void spaces between the nodules may form water channels in reverse osmosis and ultraflltration. They may also become defects when they appear at the densely packed monolayer of nodules or nodular aggregates. Information on the nodular structure will therefore help to eliminate the unwanted defects in the skin layer of the asymmetric membranes. 

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