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Abstract There are four superimposed tiers of structure in integrally skinned phase inversion membranes: macromolecules (functionally submacromolecules, that is, displacements between chain segments); nodules –approximately 200 Å in diameter spherical macromolecular aggregates, each of which contains several tens of macromolecules (nodule interiors are denser than interstitial regimes, therefore, chain segment displacements within and between nodules differ and hence constitute a bimodal pore size distribution which may account for the dual mode sorption and permeation of gases; transport of water in reverse osmosis occurs primarily through the less dense interstitial domains); nodule aggregates —400–1000 Å in diameter spherical clumps of nodules (the skins of reverse osmosis and gas separation membranes consist of a single layer of coalesced nodule aggregates; ultrafiltration pores are the spaces between incompletely coalesced nodule aggregates, and residual ultrafiltration pores are the defect pores found in reverse osmosis membrances); supernodular aggregates –aggregates of nodule aggregates which constitute the walls of the 0.1–2 μm in diameter open cells in the membrance substructure (microfiltration pores are the surface extensions of openings between adjacent cell walls).
R. E. Kesting (Mon,) studied this question.