Finger-like pores

In preparing membranes via the phase inversion process for applications in pressure-driven processes, the formation of macrovoids should be avoided completely. These finger-like pores of the type present in the substructure of membranes (b) and (c) of Fig. 3.6-1, severely Hmit the compaction resistance of the membrane. Membranes with a sponge-Hke structure (Fig. 3.6-la) are to be preferred. 

Most ultra-filtration membranes have an asymmetric structure with fine pores in the surface layer and coarser finger-like pores below. 

Apart from dyes and surfactants, polymeric molecules also influence the crystal habit of developing crystals. Sulfathiazole has been reported to grow out in finger-like protrusions in the presence of polyvinylpyrrolidone (PVP). It was suggested that PVP formed a net over the developing crystals. The effective pore size in the net and growth inhibition depended on the relative transport rates of PVP and sulfathiazole to crystal surface. Carbamazepine (anhydrous) is... 

In skin-type membranes, like hollow fibre membranes, two characteristic structures can be formed. One structure is sponge-like below the skin, and one has finger-shaped pores below the skin. These finger-shaped pores can be clearly seen in the polyetherketone hollow fibre (see Fig. 11.5)." " " ... 

Chemical processes work either to change the mobility of a displacing fluid like water, or to reduce the capillary trapping of oil in the rock matrix pores. Reducing the mobility of water, for example by adding polymers, helps to prevent fingering, in which the less viscous water bypasses the oil and... 

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