NODULAR STRUCTURE OF POLYMERS IN THE MEMBRANE

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 structures were found not only in the ultrathin and asymmetric membranes but also at the surface of thin film composite (TFC) membranes. Cadotte reported that nodules were closely packed at the surface of a fully aromatic polyamide TFC membrane prepared by the in situ polycondensation reaction between m-phenylene diamine and trimesoyl chloride [3,4]. 

nodular structures are always found at the surface of polymeric membranes. Based on the size of the structural units, Resting suggested the following four superimposed tiers of structure in asymmetric membranes prepared by the phase inversion technique [5]  

Nodules—spherical macromolecular aggregates, approximately 200 A in diameter, each of which contains several tens of thousands of macromolecules 

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

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