Diameter of nodules

Morphology studies done by tapping mode atomic force microscope revealed that membranes prepared from a PPO solution with 2-ethyl-1-hexanol as the additive had the lowest mean diameter of nodules. Interestingly these were the membranes that exhibited the highest permeance ratio of 5.5 for O2/N2 24.5 for CO2/CH4 (second highest after 1-octanol). Pure gas... 

It can be noticed that both surfaces show a relatively uniform nodular structure however, nodules on the bottom surface (davg = 137.5 nm) are twice as large as those on the top surface (davg = 63.8 nm). A summary of the measurements of the diameters of nodules for both homogeneous and asymmetric membranes is presented in Table 10. 

The difference in the diameter of nodules on the top and bottom surfaces of homogeneous membrane could be caused by a difference of solvent evaporation across the membrane, i.e., the evaporation rate of solvent at the top surface was faster than on the bottom surface. The difference in the evaporation rates increases with the volatility of the solvent and an increase in the initial pol)mier concentration. 

Table 24. Mean diameter of nodule plus length of crevice for coupons etched to a maximum of 60 sec and 120 sec...

Etching time Mean diameter of nodule plus lengt... 

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. 

Severe recalcitrant nodular acne Nodules are inflammatory lesions with a diameter of 5 mm or greater. The nodules may become suppurative or hemorrhagic. Severe, ... 

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... 

One might expect the nodule diameter of pure LDPE to be the same as that in the amorphous rubber/LDPE blend. This could result if the same proportion of LDPE nucleated the crystals and if no amorphous EPDM lay inside the LDPE crystallites. However, the concentration of crystallites would be lower in the blend. It is impossible for us to measure the concentration of crystallites in this blend. The resolution is inadequate and the etching depth is not accurately known. We will have to look at blends containing less LDPE to see if the crystallite concentration decreases. No spherulites are seen in these blends by polarized optical microscopy. However, these nodules are too small for optical resolution, and may indeed be spherulites or aggregates of lamellae. 

Spectroscopic studies of the structure of Nafion membranes suggest the presence of nodules of diameter 1-10 run (the lighter parts in Fig. 3.43). The nodules are fairly regularly distributed and have been explained as spherical... 

Schulz and Asumnaa (48), based on their SEM observation, assumed that the selective layer of an asymmetric cellulose acetate membrane for reverse osmosis consists of closely packed spherical nodules with a diameter of 18.8 nm. Water flows through the void spaces between the nodules. Calculate the water flux by Eq. (30) assuming circular pores, the cross-sectional area of which is equal to the area of the triangular void surrounded by three circles with a diameter of 18.8 nm (as shown in Eig. 8). 

Buried nodules Most workers on the subject agree that the preferential concentration of nodules at the sediment surface is due to the activity of benthic organisms which can slightly move the nodules. Buried nodules have, however, been found in all the oceans of the world. Their abundance is highly variable, but it is possible that it may not be entirely random. Buried nodules recovered in large diameter cores are sometimes concentrated in distinct layers. These layers may represent ancient erosion surfaces or surfaces of nondeposition on which manganese nodules were concentrated in the past. By contrast, in the Peru Basin large asymmetrical nodules get buried when their bottoms get stuck in tenacious suboxic sediment just below the surface layer. 

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. 

Fig. 10.1. Changes in tumor burden after therapy. The sum of maximal diameters of target lesions according to RECIST criteria is shown in black solid lines. Number of patients developing new tumor nodules within the liver are shown in bars...

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. 

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