Porous media swelling

Two main types of gel material may be distinguished xerogels and aerogels. Xerogels are gels in the classical sense they consist of cross-linked polymers which swell in contact with the solvent to form a relatively soft porous medium, in which the pores are the spaces between the polymer chains in the matrix. If the liquid is removed the gel structure collapses, although it... 

The porous medium (sorbent, membrane, gel particle) can be made of soft spherical particles that swell quite a bit when immersed in a solvent they are called gek. If they swell in water, they are called hydrogels however, the polymers are crosslinked so that they retain their overall structure. Of course, the polymers are soft and compress under pressure a typical example would be gels (which are crosslinked) based on agarose (Figure 3.3.5B). Such gel particles are widely used in a variety of separation techniques for separating macromolecules/proteins, etc. 

The pemeabihty of a porous medium, defined by Darcy s law, is called Darcy permeability which has dimensions NT L T. However, the permeability so defined depends both on the material and on the fluid. For permeation flows which are geometrically similar (in practice, Newtonian liquids in laminar flow in inert non-swelling media), the Darcy permeability varies inversely with the fluid viscosity r]. Therefore, an intrinsic permeabihty k can be defined, as shown in Eq. 3.24 ... 

The previous analysis of SAH behavior in the soil clearly shows that their application for improving the water-holding capacity is not universal. Hydrogel swelling in a porous, partially salinized medium is affected by numerous factors, most often negative, and therefore a rational application of SAH demands an accurate consideration of these factors. It is evident that certain principles for adjustment of hydrogels to physical and chemical soil parameters, as well as appropriate laboratory tests and calculation algorithm systems should be worked out. 

Usually crosslinking of linear polystyrene even in a more concentrated solution, 0.125 g/mL, in EDC results in the formation of highly porous materials with the apparent specific surface area of 1000 m/g, while further dilution changes the porosity only insignificantly.) Porous crosslinked polyarylates swell in n-heptane, a precipitating medium for the polymer precursor, and, therefore, they also belong to the family of hypercrosslinked polymers. 

For example, the original manbrane of 10 kDa presented the average pore size of 0.038 pm, and after pretreatment, the size was 0.075 pm, while the original membrane of 50 kDa was 0.02-0.04 pm of medium pore size. This effect was probably due to different properties of mass transfer and the swelling capacity of the structure of the thin surface layer on the manhrane of 10 (dense) and 50 kDa (porous). Isopropanol promotes by the swelling effect, leading to a more open of the pores, as a spongy structure. 

The resultant porous sheet can be used as a filter medium, but if the untreated paper gets wet then the fibres absorb moisture, with two significant consequences the fibres swell, so that the spaces between them reduce and the paper improves in filtration efficiency, but the mechanical strength drops sharply, making the paper less useful as a filter. To be used as a filter, then, the paper must be fully supported for use in wet filtration (as, for example, in the filter papers used in the laboratory filter funnel) or it must be restricted to dry filtration (such as in building air cleaning). 

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