Nodules merged

All the above effects indicate that the selectivity (permeance ratio) of the PPO membrane (asymmetric) increases as the close-packing of the nodules and polymer entanglement between nodules are enhanced. In fact, it was observed that the membrane selectivities increased when nodules merged and roughness parameter decreased. 

Khulbe et ah [20] and Tan et al. [21,22[ both stated that smoother membrane surfaces, formed as a result of the merging of nodules, would enhance the selectivity of membranes when they were used for gas separation. This concept has not been proven by other researchers since few people have apphed the AFM technique to study gas separation membranes. Combined with plasma etching, the AFM technique will provide detailed information on the surface morphology of gas separation membranes, which will definitely influence the future of gas separation membrane design. 

In the Wistar rat, lymphoid aggregates of the bronchi and bronchioles varied from small collections of mononuclear cells limited to the lamina propria of the airway to large nodules that extended through the muscularis and merged into the peribronchial connective tissue or the walls of adjacent alveoli (Chamberlain et al. 1973). 

Fig. 6.10a,b. Coal worker s pneumoconiosis computed tomography scan showing micronodular and nodular lung and subpleural involvement. a,b Axial views with slice thickness of 5 mm. Micronodules grow and merge, and nodules develop (arrows). Notice also the subpleural focal area of increased opacity (a) pseudo plaque , which should be differentiated from real pleural plaques related to asbestos exposure (arrow)... 

The mean roughness increases with an increase of the boiling point with only one exception of trichloroethylene solvent (PPO-TCE). PPO-CS2 showed the lowest roughness among other membranes, which is very natural since the groove between nodules becomes shallower when nodules are merged by aggregation. 

Figure 39. Pure O2/N2 permeance ratio as a function of mean nodule diameter of numbered nonsolvent additives. Legend (1) 2-ethyl-1-hexanol (2) 1-octanol (3) 2- propanol (4) 2-decanol (5) 3,5,5-trimethyl-1-hexanol (6) 2,4-dimethyl-3-pentanol (7)2,4,4-trimethyl-l-pentanol (8) 2,2-dimethyl-3-pentanol (9) 3-ethyl-2,2-dimethyl-3-pentanol (12) 3-ethyl-3-pentanol m merged d discrete.

Figure 42.3D AFM images of merged nodules of 2-ethyl-1-hexanol.

According to the Young-Laplace equation, the capillary pressure increases as the surface tension of the interstitial fluid increases and decreases as the effective radius of the interstitial space increases. The formation of nodules and their packing, whether merged or discrete depends upon the capillary pressure that exists at the polymer-solvent-nonsolvent additive interface. This... 

The effect of the surface tension of chloroform-nonsolvent additive systems on the formation of nodules are reflected in the correlation between surface tension and pure O2/N2 (Figure 44) and CO2/CH4 (Figure 45) permeance rate ratios. Both figures show that as the surface tension increased, the pure gas permeance rate ratios increased. Also, most of the membranes with merged nodules are found in the range of surface tensions greater than... 

From both these figures, it can be seen that long chain alcohols of nonsolvent additives tend to result in solvent-nonsolvent additive solutions with higher surface tension and membranes with merged nodules. This results in higher pure O2/N2 and CO2/CH4 permeance rate ratios. Lower pure O2/N2 and CO2/CH4 permeance rate ratios are expected when shorter and highly branched chain alcohols were used. They produced membranes with discrete nodules due to lower surface tensions in their solvent-nonsolvent additive solutions. 

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