Sponge-type structure

Figure 7. Photo-micrographs of the casting solution/precipitant interphase at (a) the beginning of the precipitation and after (b) 12 sec., (c) 2 f sec. and (d) 5 min. Series I giving a "finger"-type structure and series II giving a "sponge"-type structure.

Figure 1.14 Scanning electron micrograph of membrane cross sections with typical structures (a) symmetric microporous membrane without a "skin" (b) asymmetric membrane with a "finger"-type structure and a dense skin at the surface (c) asymmetric membrane with a "sponge"-type structure, a dense skin, and pore sizes increasing from the surface to the bottom side (d) symmetric membrane with a sponge structure, a dense skin and a uniform pore size distribution in the substructure.

Figure 1.15 Scanning electron micrographs of the fine structure of two phese inversion membranes (a) sponge-type structure consisting of spherical cells (b nodular structure consisting of small polymer beads fused together to form a randomly porous structure.

There are marked minima in the curves for isopar M and cyclohexane. These correspond to the optimal HLB values HLBopt 9 for AM and 12 for MADQUAT. Such values are much greater than those used in forming water-in-oil emulsions, for which the HLB lies in the range 4-6. This indicates that the systems are located in a phase inversion zone and have sponge-type structure. 

Fig. 2.2 Piston flow of water infiltrating into a homogeneous granular soil (sponge-type flow). A layered structure is formed, lower water layers being older than shallow ones. Penetration velocities are observed to range from a few centimeters to a few meters per year.

Fig. 1 shows the porous silicon structures formed on different silicon wafers. Porous silicon on p-type wafer is characteri d by a sponge-like structure with pore wall thickness of 2-4 nm and 5-6 rnn for wafers with resistivity of 12 and 0.03 Q cm, respectively (Fig. la,b). Porous silicon on n-type silicon (0.01 Q cm) shows a branch-like structure (Fig. lc,d). In this case mother pores branch out and form the daughter pores. The pore wall thickness is 7-10 nm for porous silicon anodized with the light exposition (Fig. Ic) and 15-20 nm for porous silicon anodized without the light exposition (Fig. Id). 

Sponges contain structures that support the cell layers and give the animals shape. In many types of sponges, these structures are small, mineralized needles called spicules that are scattered throughout the mesoglea. Instead of spicules, some species possess fibers made of a tough, rubbery protein called spongin. 

The H-bond complexes formed between phenol derivatives and bis-l,8-(dimethylamino)-naphthalene (175) in 1,2-dichloroethane and tetrachloroethylene solution were characterized by FTIR spectroscopy. Compound 175 acts as an effective proton sponge for its ability to form a six-membered chelate-type structure including aN H N moiety. The stability constants of the 1 1 and 2 1 complexes are strongly dependent on the pXa value of the phenols and increase also with the polarity of the solvent. No complex formation was detected in tetrachloroethylene when H was replaced by... 

This is the usual type of HPLC stationary phase. These materials are 1.8, 3.0, 3.5, 5.0 or 10 gm in size. As a rule of thumb, their performance, i.e. the plate number per unit length, doubles each time from 10 to 5 and 3 gm, whereas the pressure drop increases each time by a factor of four. Their internal structure is fully porous and can best be compared with the appearance of a sponge (however, in contrast to a sponge, the structure is very rigid). Within the pores the mobile phase (and the analytes) does not flow but moves only by diffusion. 

Halicyclamine A (346) was isolated from a marine sponge Halicona sp [727], Its structure was determined using HREIMS, EIMS, IR, and one- and two-dimensional 1h and 13C NMR. While 346 appears similar to the haliclamines (345), it was suggested that 346 may arise biosynthetically from cleavage of the C(18)-C(33) bond in the xestocyclamine/ingenamine type structure D [727]. 

Skin Type Membranes With "Sponge"- and "Finger"-Like Structures. In skin-type membranes, the two characteristic structures shown in Figure 1.14 are obtained. One is a sponge-like structure and the other is a finger-like substructure underneath the skin. 

An ab initio study of structure and bonding in diphosphinylcarbenes indicates that the non-symmetric ylide-type structure (29) is preferred." The configuration and conformation of a number of polyfunctional 1-aminobuta-1,3-dienes (30), prepared by the reaction of dimethyl acetylenedicarboxylate with (Z)-P-enamino-l -phosphazenes, have been studied by n.m.r.. X-ray, and theoretical methods. The P n.m.r. spectra of a number of protonated iminophosphorane-substituted proton sponges, e g. (31), of known crystal structure have been studied in the solid state."... 

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. 

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