Interconnected pore, definition

Molecular sieves, however, are crystalline and have, therefore, an internal structure of regularly spaced cavities with interconnecting pores of definite size. Details of the properties peculiar to the various materials are best obtained directly from the manufacturer. The following is a brief description of these principal adsorbents. 

For the purposes of this review, we restrict the definition of PIMs to organic polymers which have interconnected pore structures and which exhibit appreciable apparent inner surface areas by gas sorption analysis. PIMs can be linear polymers (Sect. 2.2.1) or networks (Sect. 2.2.2). While other network polymers may be microporous (e.g. Sect. 2.1 and 2.4), it is this porosity of the linear analogues that distinguishes PIMs. Again, the area of PIMs has been reviewed quite recently [41,42] so relatively brief details are given here. 

We may begin by describing any porous medium as a solid matter containing many holes or pores, which collectively constitute an array of tortuous passages. Refer to Figure 1 for an example. The number of holes or pores is sufficiently great that a volume average is needed to estimate pertinent properties. Pores that occupy a definite fraction of the bulk volume constitute a complex network of voids. The maimer in which holes or pores are embedded, the extent of their interconnection, and their location, size and shape characterize the porous medium. 

The possibility of obtaining different pore sizes and geometries allows studying the specific role of the pore diameter and interconnection in confinement effects. However, the main problem in the use of MCM materials in radiolysis is the poor definition of the silica-based walls. The presence of micropores and a high content in non-condensed silica (silanols groups) has been evidenced in some cases. 

The pores in the pellet are not straight and cylindrical rather, they are a series of tortuous, interconnecting paths of pore bodies and pore throats with varying cross-sectional areas. It would not be fimitfiil to describe diffusion within each and every one of the tortuous pathways individually consequently, we shall define an effective diffusion coefficient so as to describe the average diffusion taking place at any position r in the pellet. We shall consider only radial variations in the concentration the radial flux will be based on the total area (voids and solid) normal to diffusion transport (i.e., 4TTr ) rather than void area alone. This basis for is made possible by proper definition of the effective diffusivity D. ... 

The determination of the buckling constant h by calibration from mercury intrusion porosimetry, or from nitrogen adsorption-desorption, can lead in some cases to different results. It is likely that, beyond the imprecision due to the method, the differences in pore sizes observed arise from a fundamental difference in the pore size concept. lUPAC proposed to define pore size as the distance between two opposite pore walls (Rouquerol, 1994). In the case of materials from the sol-gel process, this definition is not applicable, because pores are not included between walls, but are only delimited by interconnected filaments. In practice, it is considered that the sizes obtained from analysis methods of the texture of porous materials are characteristic pore sizes. Because the different analysis methods are based on different physical phenomena, it is not astonishing that they lead to slightly different characteristic pore sizes. Discrepancies resulting from using different characterization methods appear in several publications, often when the same material is analyzed by nitrogen adsorption-desorption and mercmy intrusion porosimetry (Smith, 1990, Brown, 1974, Milburn, 1988, Minihan, 1994). Me Enaney et al. noted that the distribution profiles obtained by different characterization techniques are often similar, but that differences, sometimes important, between the absolute values of characteristic pore sizes are almost unavoidable (Me Enaney et al., 1995). 

---