Micropores morphology

A rigid microporous morphology, which does not reorganize upon water uptake, corresponds to a simple linear relation x w) = yw. In this limiting case, the model resembles the archetypal problem of percolation in bicontin-uous random media. Due to deviations of swelling from fhis law, universal percolation exponents in relations between conductivity and water content are not warranted. 

The first stage in the interpretation of a physisorption isotherm is to identify the isotherm type and hence the nature of the adsorption process(es) monolayer-multilayer adsorption, capillary condensation or micropore filling. If the isotherm exhibits low-pressure hysteresis (i.e. at p/p° < 0 4, with nitrogen at 77 K) the technique should be checked to establish the degree of accuracy and reproducibility of the measurements. In certain cases it is possible to relate the hysteresis loop to the morphology of the adsorbent (e.g. a Type B loop can be associated with slit-shaped pores or platey particles). 

Figure 3. Schematic representation of the micro- and nanoscale morphology of gel-type (a) and macroreticular (b) resins [13], Level 1 is the representation of the dry materials. Level 2 is the representation of the microporous swollen materials at the same linear scale swelling involves the whole polymeric mass in the gel-type resin (2a) and the macropore walls in the macroreticular resin (2b). The morphology of the swollen polymer mass is similar in both gel-type and macroreticular resins (3a,b). Nanopores are actually formed by the void space surrounding the polymeric chains, as shown in level 4, and are a few nanometer wide. (Reprinted from Ref [12], 2003, with permission from Elsevier.)...

Irrespectively of the iron content, the applied synthesis procedure yielded highly crystalline microporous products i.e. the Fe-ZSM-22 zeolite. No contamination with other microporous phases or unreacted amorphous material was detected. The SEM analysis revealed that size and morphology of the crystals depended on the Si/Fe ratio. The ZSM-22 samples poor in Fe (Si/Fe=150) consisted of rice-like isolated crystals up to 5 p. On the other hand the preparation with a high iron content (Fe=27, 36) consisted of agglomerates of very small (<0.5 p) poorly defined crystals. The incorporation of Fe3+ into the framework positions was confirmed by XRD - an increase of the unit cell parameters with the increase in the number of the Fe atoms introduced into the framework was observed, and by IR - the Si-OH-Fe band at 3620 cm 1 appeared in the spectra of activated Fe-TON samples. 

PCA [Precipitation with a compressed anti-solvent] A process for making a solid with unusual morphology by spraying a solution of it into a supercritical fluid. The process resembles spray drying into a supercritical fluid. Used for making microspheres, microporous fibers, and hollow microporous fibers. 

Recently, the micropore range has been subdivided into two additional categories very narrow pores or ultramicropores (<0.7 to 1.0 nm), where the enhancement effect is found and supermi-cropores (0.7 to 2.0 nm), which fill the gap between the ultramicropores and mesopore ranges [53, 115], This classification has become widespread, but it only takes into account adsorption effects and ignores the morphology of PS elements and their integrity. 

The blends could exhibit different morphologies continuous or microporous [46],... 

The average pore size of PS structures covers four orders of magnitude, from nanometers to tens of micrometers. The pore size, or more precisely the pore width d, is defined as the distance between two opposite walls of the pore. It so happens that the different size regimes of PS characterized by different pore morphologies and different formation mechanisms closely match the classification of porous media, as laid down in the IUPAC convention [Iu2]. Therefore the PS structures discussed in the next three chapters will be ordered according to the pore diameters as mostly microporous (d<2 nm), mostly mesoporous (2 nm50 rim). Note that the term nanoporous is sometimes used in the literature for the microporous size regime. 

An extension of this QC model, including tunneling probabilities between the confined crystallites and the bulk, has been developed [Fr6]. The QC model for microporous silicon formation, however, is still qualitative in character, and a quantitative correlation between anodization parameters and the morphology and properties of the porous structure is at yet beyond the capability of the model. 

The effective conductivity of the membrane depends on its random heterogeneous morphology—namely, the size distribution and connectivity of fhe proton-bearing aqueous pafhways. On fhe basis of the cluster network model, a random network model of microporous PEMs was developed in Eikerling ef al. If included effecfs of varying connectivity of the pore network and of swelling of pores upon water uptake. The model was applied to exploring the dependence of membrane conductivity on water content and... 

---