Pore size distribution model silica glasses

It is not easy to perform measurements of kinetics of polymer adsorption or exchange in porous systems. Pore geometries, even in model systems like con-trolled-pore glass or Stober silicas, are usually poorly denned. In situ measurements are difficult to perform. Usually, indirect measurements are performed in which one measures batchwise the time dependence of the concentration of the polymer in intensively stirred bulk solutions. As discussed above, depending on the size of the polymer and the pore radius, adsorption can be extremely slow. Of course, one must realize that even in model porous systems nonideality of the pore geometry, such as the presence of tortuous pore channels with junctions and branches, a pore size distribution, and a non-uniform pore diameter, may thwart the interpretation of experimental results. 

The most commonly used model for pore topology is to represent the material as composed of independent, non-interconnected pores of some simple geometry usually these are of slit shape for activated carbons, and of cylindrical geometry for glasses, oxides, silicas, etc. Usually, the heterogeneity is approximated by a distribution of pore sizes, it being implicitly assumed that all pores are of the same geometry and surface chemistry. In this case the excess adsorption, f(P), at a pressure P can be represented by... 

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