Diameter of the nodule

The diameter of the nodules appears to be 20 and 16 nm for S and M membranes, respectively. For the H membrane, supernodular aggregates of 620 nm contained 6-8 nodule aggregates of 140 nm (Fig. 4.27). In addition to their small diameter (12 nm), the Si02 nodules are more discernable than those of M and S membranes. 

Figure 4.36a-d is for samples taken from inner surface of a hollow fiber spun at a 10-cm air gap. From the surface images a and b, the diameters of the nodule aggregates were obtained and the results shown in Table 4.9. Again, no significant difference in diameter was observed between samples a and b. However, Fig. 4.36a appears very similar to Fig. 4.36b. 

Figures 4.38 and 4.39 show, respectively, the AFM images of the outer surfaces of the hollow fibers spun at the air gaps of 1 cm and 10 cm. Again, a and b are the surface images of two samples taken from two different sites along a hoUow fiber, while c and d are the three-dimensional images of another two sites. The sizes (diameters) of the nodule aggregates summarized in Table 4.9 show that ...

The first observation mutually confirms the nodules sizes observed either by SEM or by AFM. The second observation is expected because the coagulation of the polymer occurs soon after the extrusion of the casting dope from the spinneret, when it is brought into contact with the bore fluid (water). The third observation is similar to the result obtained by Fujii et al. [13] for their PAN hollow fiber, in which the mean diameters of the nodules, called spheres in their paper, are reported at the area near the inner surface, in the middle section, and at the area near the outer surface to be 118.0,166.0, and 109.0 nm, respectively. The fourth observation is probably due to the stretching of the outer surface that occurs while the hollow fiber is traveling through the air gap. 

On the floor of the ocean, at a depth of approximately 4000 m, so-caUed manganese nodules may be found (Figure M42). They are manganese and other metal oxides and clay. Nodules of economic interest contain 25-30% Mn, 1.5% Ni, 1.2% Cu, 0.3% Co and 0.05% Mo. The diameter of the nodules is on average 50 mm but the size varies... 

Comparison of top surfaces of the dense and asymmetric membrane indicates that there are some small differences between morphologies of these surfaces. The average diameter of the nodules (davg = 30.97 nm) in the top layer of dense membrane is less than the average diameter of the nodules in the top layer of asymmetric membrane (davg= 36.79 nm). Inspite of that, the roughness parameters for the top layer of the dense membrane are greater than those for the top layer of the asymmetric membrane. 

This can be proven by adding the length of the crevices between the nodules to the diameter of the nodules of coupons etched for 60 and 120 sec to yield a constant value, regardless of the etching time. The results are shown in Table 24. The measurement for the length of crevices is also given in Figure SQ... 

They have diameters of 2 to more than 8 cm. The substratum of the nodules is shark teeth, basalts, andesites, and more rare varieties of weathered volcanic rocks. 

Figure 9 shows SEM photomicrographs of ion-etched surfaces of blends of LDPE/amorphous Epcar 845 and of LDPE/crystalline Epcar 847. Nodule diameters of the LDPE/amorphous rubber blend average... 

Spherically shaped structures can occasionally be electron microscopically observed with polymers. The diameters of these nodules vary between 2-4 nm for poly(styrene) and about 8 nm for poly(ethylene terephthalate). It is still a matter of controversy as to whether these structures are real or are experimental artifacts caused by insufficient focusing, surface effects produced by fracture or in the sample preparation, etc. 

NC-AFM is better than C-AFM for imaging small pores such as those in ultrafiltration and nanofiltration membranes. The reason for this is that the diameter of the cantilever tip apex is greater than the pore diameter. When the tip is passed over the small pore, the tip cannot penetrate into the pore, and there will not be a great change in cantilever deflection. However, TM-AFM is more successful at measiuing the pore size and nodule size on the membrane surface. 

Nodules are defined as spherical cells with a diameter of a few hundred angstroms that are compacted irregularly at the membrane surface. They can also be observed underneath the membrane surface when a cross-sectional picture is taken. Each nodule contains several tens of thousands of macromolecules. Schultz and Asunmaa were the first to report the observation of nodules on the surface of an ultrathin cellulose acetate membrane by electron microscope [1]. Figure 4.1 shows the picture taken by them. The nodular structure of the membrane surface is clearly seen with an average nodular diameter of 188 3 A. The same authors also took a picture of an asymmetric cellulose acetate membrane and found that it, too, had a nodular structure. Panar et al. [2] then observed the close monolayer packing of micelles with diameters from 400 to 800 A when a cross-sectional picture of an asymmetric aromatic polyamide-hydrazide membrane was taken (Fig. 4.2). The top monolayer covers a support layer where the spherical micelles are irregularly packed with void spaces of 75-100 A. They attributed the formation of the nodules to the micellar structure that was initially present at the surface of the polyamidehydrazide solution. 

Khayet et al. [31] studied the surfaces of asymmetric poly(etherimide) (PEI) ultrafiltration membranes by AFM. Membranes were prepared by casting mixtures of PEI, hydroxybutyric acid y-lactone (GBL, y-butyrolactone) as nonsolvent and N,N-dimethylacetamide (DMAc) at 50 °C. The average size of the nodule aggregates versus PEI concentration is given in Fig. 4.16. From Fig. 4.16, it is clear that the nodule aggregate diameter increases as the PEI concentration increases. 

Broadhead and Tresco studied the effects of fabrication conditions on the structures and performances of membranes formed from poly(acrylonitrile-vinylchloride) (PAN-PVC) by using the phase inversion process [85]. They reported the relationship of the fine-surface structure of PAN-PVC membranes to the membrane performance and membrane fabrication method. The fine-surface structure of nodular elements and the size of these elements could be altered by changing the precipitation conditions. Membranes were prepared at 22 on 55 mm diameter polished silicon wafers by spinning at 1500 rpm for 20 s with a spin coater [86]. The film was immediately precipitated in one of the four different precipitation media. The first three media consisted of deionized water at 4,22, and 54 °C. These membranes were referred to as Type 1 , Type 2 , and Type 3 , respectively. The fourth medium was a 50/50 mixture of deionized water and N,iV-dimethylformamide (DMF) at 54 °C and coded as Type 4 . Figure 4.53 shows the histograms of the nodule size distributions observed at the skinned surface of the membranes made under four different precipitation conditions. The sizes of these nodular elements became smaller and more uniform with milder precipitation conditions, which supports the theory that nodules are formed through spinodal decomposition under these conditions. In addition, the size of these nodules could be related to water permeability. Hence, water transport occurred through the interstitial spaces where the pores could be situated. 

The carhon blacks are characterized by their chemical compositions, microstructure, morphologies, and the physical chemistry of the surface. Morphology is a set of properties related to the average magnitude and frequency distribution of the nodule diameter, aggregate diameter, and the way nodules are connected in the aggregates. 

The earliest histological feature is proliferation of Langerhans cells found around terminal and respiratory bronchioles (3,21). These early cellular lesions expand to form nodules that are typically 1 to 6 mm in diameter (21). These bronchiolo-centric nodules characteristically have a stellate configuration (Fig. la). The morphology of the nodules varies with the activity of the lesions. Early lesions are cellular. The peribronchiolar interstitium and adjacent alveolar septa are thickened by clusters of Langerhans cells admixed with variable numbers of eosinophils, neutrophils, lymphocytes, macrophages, and fibroblasts. Eosinophils are often numerous and can form eosinophilic abscesses but may be absent in up to 20% of... 

Table 15. Estimated nodule diameters of the SPPO coating layers as a function of chloroform...

Table 10. Summaiy of the measurement of small nodule diameters of the membranes, prepared using chloroform as solvent...

The nodule diameters of the top and bottom surface are different for dense homogeneous membrane. 

A rich supply of manganese lies in nodules of ore that litter the ocean floors (Fig. 16.9). These nodules range in diameter from millimeters to meters and are lumps of the oxides of iron, manganese, and other elements. However, because this source is technically difficult to exploit, manganese is currently obtained by the thermite process from pyrolusite, a mineral form of manganese dioxide ... 

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