Nodular aggregate

The Worm of the alcohol can be obtained in 85-90% purity from the combined acetone and final methanol mother liquors by a rather laborious process of fractional crystallization aided by mechanical separation.137 140 Thus on long standing the acetone solution may deposit characteristic nodular aggregates of leaflets of nearly pure brucine 1-8-butyl phthalate, [a]n — 18.0° these are separated by filtration or decantation. The solution, upon concentration, may then yield more of the crude d-salt and then again the 1-salt. The method is tedious but gives rather good yields, especially when large quantities of material may be worked up in a leisurely fashion. 

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... 

Supernodular aggregates—aggregates of nodular aggregates, from 1000 to 20 000 A (2 j,m) in diameter. 

As shown in Table 4.1, the mean diameter of the supernodular aggregates is 1.20 j,m. Figure 4.9 shows the AFM image of the top surface at a scan size of 1 pm. From Fig. 4.9, it seems that a supernodular aggregate contains smaller units that correspond to nodular aggregates, the mean diameter of which is 43.7 nm. Figure 4.10... 

It is interesting to note that the PPO-CS2 membrane with the supernodular aggregates exhibited the highest selectivity for the CO2/CH4 gas pair. Filling the interstitial gap between nodular aggregates may, therefore, lead to higher selectivity of the gas separation membrane. 

Table 4.4. Ranges of the sizes of nodular aggregates for different compositions of chloroform/methanol solvent mixtures...

Fig. 4.16. Average nodular aggregate size versus PEI concentration...

The size of the nodular aggregate decreased with an increase in chloroform content in the solvent mixture. This means that the compactness of the macromolecular coil in the casting solution was retained after evaporation of the solvent from the solution. 

Fig. 4.31. Arrangement and size of supernodular aggregates and nodular aggregates in dense PPO-C 2 membrane. Reprinted from [54]. Copyright 2000, with kind permission from Elsevier...

Table 4.9. Average, maximum, and minimum size (diameter) of nodular aggregates at the inner and outer surfaces of hollow fibers at air gaps 1 and 10 cm...

Nodular abrogates are assembled to a number of string-like structures and aligned in one row. The similarity between Fig. 4.36a and b most likely means that the alignment of nodular aggregates under the shear force is completed when the air... 

Comparing Figs. 4.37 and 4.40, it can be concluded that the outer surface is smoother than the inner surface. It is also interesting to note that, contrary to Chung et al.s results, there was no alignment of nodular aggregates on the outer surface to any specific direction [58]. 

Table 4.10. Average distance between the rows of nodular aggregates (inner surface) and average diameter of the nodular aggregates on the inner and outer surfece of the hollow fibers prepared at different air gaps...

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... 

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. 

Attention should be focused on the extremely high selectivity data of the PPO membrane that was cast from the PPO solution in carbon disulfide (PPO-CS2). On the surface of this membrane it was observed that several nodular aggregates merged... 

Fig. 8.5. Mean distance between supernodular aggregates at 5- xm scan range (4) and between nodular aggregates at 1- xm scan range B) in the PPO-CS2 membrane after various plasma etching times...

Finally, follicular bronchitis/bronchioMs shows peribronchial/peribronchiolar nodular aggregates of lymphoid cells that contain reactive germinal centers. The essential difference is that the lesion is confined largely to the airway, and there is no evidence of a mass by chest imaging studies (81). 

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