Pores columnar

The other type of porous glass that has cylindrical pores is mesoporous silicate (MPS) (14,15). The advantage of MPS is in its feasibility to make a small pore diameter, typically below 10 nm. A columnar-phase liquid crystal, formed from surfactant molecules with a long alkyl chain tail and silicate molecules, is calcined to remove hydrocarbons. At the end, a hexagonal array of straight and uniform cylindrical holes is created in a crystalline order. MPS is not available commercially either. 

Following initial receptor-mediated binding, toxin molecules insert into the apical membrane of columnar epidielial cells, and become resistant to proteases and monoclonal antibodies [91]. Toxin insertion subsequently induces formation of a nonspecific pore in the target membrane. Voltage-clamping studies of lipid bilayers [92 and the midgut sections [93,94 support the Actional role of toxin in pore formation. The size and selectivity of the formed pore varies with toxins and insect species, but the nature of these pores is still controversial. Alternatively, it is described as a non-specific pore that has no ion selectivity or as an ion-specific chaimel that disrupts the membrane potential [5]. 

It has long been observed that when aluminum oxidizes on its surface, the resulting structure of the oxide is rather unique in having pores of a columnar shape. Researchers have turned this unique phenomenon into synthesis of a desirable and controlled membrane pore morphology. 

Mammillary calcite is very dense, with porosities much less than 1%. Pore spaces are of two different types. The first type consists of irregularly shaped pore spaces with fluid inclusions that are commonly oriented parallel with the crystallite boundaries. In traditional speleothems, spindle-shaped inclusions mark the sites where columnar crystals have coalesced (Kendall and Broughton, 1978). In mammillary calcite, the irregular inclusions probably mark... 

Porous anodic aluminum oxide (AAO) which characterized by a closely packed regular array of columnar cells is well-established and widely-used material for formation of nanostructures for SERS [2,3]. Particularly, promising SERS-active substrates were prepared by vacuum deposition of silver onto commercially available alumina filters with open pores of 200-300 nm diameters [4], Nanowires and nanorods have been fabricated by filling the AAO pores with transition- or noble-metals. However, due to multistage procedure these nanoarrays being sensitive are rather complicated in fabrication. 

The schematic arrangement for the SANS measurements with the membrane (47 mm OD) samples is illustrated in Figures 9.(a) and 9.(b). Here the membrane has two different orientations to the incident collimated neutron beam In (a) the membrane disc is perpendicular to the beam in (b) the disc is almost parallel. (In practice, to obtain a sufficient sample area in the beam, the disc was oriented slightly ( 3°) away from the parallel axis.) The corresponding orientation of the columnar pores to the neutron beam for these two sample configurations is illustrated in Figures lO.(a) and lO.(b). 

Figure 10. Corresponding orientations of columnar pores in membranes having two different configurations shown in Figure 9.

FIGURE 6.13 Schematic representation of a section parallel to the pore axis of an elongated, columnar cell of a porous anodic alumina film. 

Figure 1.9 SEM images [34] of (a) original porous SiC surface after PECE, (b) early stage formation of columnar pore in cross-section, (c) porous surface structure 20 pm below the original surface after 90 min of RIE (the inset shows the Fourier transform of a larger area of this picture), and (d) the self-ordered columnar porous structure below the cap layer in cross-section. Reproduced from Y. Ke, R.P. Devaty and W.J. Choyke, Self-ordered nanocolumnar pore formation in the photoelectro-chemical etching of 6H SiC, Electrochem. Solid-State Lett., 10(7), K24-K27 (2007). Copyright 2007, with permission from The Electrochemical Society...

Based on the weight loss during the PEC process measured using the microbalance, the porosity is estimated to be 0.1. Because the columnar pores are generally uniform throughout the porous layer, it is reasonable to assume that the columnar porous structure we obtain is comparable with a perfect hexagonal packed cylindrical pore lattice. For such a pore lattice, the porosity P can be calculated using ... 

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