Dispersion permeability

Sethia S, and Squillante E (2004) In vitro-in vivo evaluation of supercritical processed solid dispersions Permeability and viability assessment in Caco-2 cells. J. Pharm. Sci. 93 2985-2993. 

PDMS based siloxane polymers wet and spread easily on most surfaces as their surface tensions are less than the critical surface tensions of most substrates. This thermodynamically driven property ensures that surface irregularities and pores are filled with adhesive, giving an interfacial phase that is continuous and without voids. The gas permeability of the silicone will allow any gases trapped at the interface to be displaced. Thus, maximum van der Waals and London dispersion intermolecular interactions are obtained at the silicone-substrate interface. It must be noted that suitable liquids reaching the adhesive-substrate interface would immediately interfere with these intermolecular interactions and displace the adhesive from the surface. For example, a study that involved curing a one-part alkoxy terminated silicone adhesive against a wafer of alumina, has shown that water will theoretically displace the cured silicone from the surface of the wafer if physisorption was the sole interaction between the surfaces [38]. Moreover, all these low energy bonds would be thermally sensitive and reversible. 

Coimectivity is a term that describes the arrangement and number of pore coimections. For monosize pores, coimectivity is the average number of pores per junction. The term represents a macroscopic measure of the number of pores at a junction. Connectivity correlates with permeability, but caimot be used alone to predict permeability except in certain limiting cases. Difficulties in conceptual simplifications result from replacing the real porous medium with macroscopic parameters that are averages and that relate to some idealized model of the medium. Tortuosity and connectivity are different features of the pore structure and are useful to interpret macroscopic flow properties, such as permeability, capillary pressure and dispersion. 

In Sec. 3 our presentation is focused on the most important results obtained by different authors in the framework of the rephca Ornstein-Zernike (ROZ) integral equations and by simulations of simple fluids in microporous matrices. For illustrative purposes, we discuss some original results obtained recently in our laboratory. Those allow us to show the application of the ROZ equations to the structure and thermodynamics of fluids adsorbed in disordered porous media. In particular, we present a solution of the ROZ equations for a hard sphere mixture that is highly asymmetric by size, adsorbed in a matrix of hard spheres. This example is relevant in describing the structure of colloidal dispersions in a disordered microporous medium. On the other hand, we present some of the results for the adsorption of a hard sphere fluid in a disordered medium of spherical permeable membranes. The theory developed for the description of this model agrees well with computer simulation data. Finally, in this section we demonstrate the applications of the ROZ theory and present simulation data for adsorption of a hard sphere fluid in a matrix of short chain molecules. This example serves to show the relevance of the theory of Wertheim to chemical association for a set of problems focused on adsorption of fluids and mixtures in disordered microporous matrices prepared by polymerization of species. 

Prepared saltwater completion fluids are made of fresh surface water, with sufficient salts added to produce the proper salt concentration. Usually, the addition of 5 to 10% NaCl, 2% CaClj, or 2% KCl is considered satisfactory for clay inhibition in most formations. Sodium chloride solutions have been extensively used for many years as completion fluids these brines have densities up to 10 Ib/gal. Calcium chloride solutions may have densities up to 11.7 lb/ gal. The limitations of CaClj solutions are (1) flocculation of certain clays, causing permeability reduction, and (2) high pH (10 to 10.5) that may accelerate formation clays dispersion. In such cases, CaC12-based completion fluids should be replaced with potassium chloride solutions. Other clear brines can be formulated using various salts over wide range of densities, as shown in Figure 4-123 [28]. 

Hurst (19) discusses the similarity in action of the pyrethrins and of DDT as indicated by a dispersant action on the lipids of insect cuticle and internal tissue. He has developed an elaborate theory of contact insecticidal action but provides no experimental data. Hurst believes that the susceptibility to insecticides depends partially on the cuticular permeability, but more fundamentally on the effects on internal tissue receptors which control oxidative metabolism or oxidative enzyme systems. The access of pyrethrins to insects, for example, is facilitated by adsorption and storage in the lipophilic layers of the epicuticle. The epicuticle is to be regarded as a lipoprotein mosaic consisting of alternating patches of lipid and protein receptors which are sites of oxidase activity. Such a condition exists in both the hydrophilic type of cuticle found in larvae of Calliphora and Phormia and in the waxy cuticle of Tenebrio larvae. Hurst explains pyrethrinization as a preliminary narcosis or knockdown phase in which oxidase action is blocked by adsorption of the insecticide on the lipoprotein tissue components, followed by death when further dispersant action of the insecticide results in an irreversible increase in the phenoloxidase activity as a result of the displacement of protective lipids. This increase in phenoloxidase activity is accompanied by the accumulation of toxic quinoid metabolites in the blood and tissues—for example, O-quinones which would block substrate access to normal enzyme systems. The varying degrees of susceptibility shown by different insect species to an insecticide may be explainable not only in terms of differences in cuticle make-up but also as internal factors associated with the stability of oxidase systems. 

Soils properties are very sensitive to the type of exchangeable ions. Calcium imparts favorable physical properties to the soil, while adsorbed sodium causes clay dispersion and swelling. It is generally recognized that an exchangeable sodium percentage of 10 is sufficient to cause soil dispersion, reduction of soil permeability and impaired growth of some crop plants. On the other hand, excess salt concentration prevents the dispersive effect of adsorbed sodium. 

Tsou and Measmer examined the dispersion of organosUicates on two different butyl mbbers, namely BIMS and brominated poly(isobutylene-co-isoprene) (BIIR) with the help of small angle X-ray scattering (SAXS), wide angle X-ray scattering (WAXS), atomic force microscopy (AFM), and TEM [91]. There is also a patent on BIMS nanocomposites for low permeability and their uses in tire inner tubes [92]. 

A surface is that part of an object which is in direct contact with its environment and hence, is most affected by it. The surface properties of solid organic polymers have a strong impact on many, if not most, of their apphcations. The properties and structure of these surfaces are, therefore, of utmost importance. The chemical stmcture and thermodynamic state of polymer surfaces are important factors that determine many of their practical characteristics. Examples of properties affected by polymer surface stmcture include adhesion, wettability, friction, coatability, permeability, dyeabil-ity, gloss, corrosion, surface electrostatic charging, cellular recognition, and biocompatibility. Interfacial characteristics of polymer systems control the domain size and the stability of polymer-polymer dispersions, adhesive strength of laminates and composites, cohesive strength of polymer blends, mechanical properties of adhesive joints, etc. 

The lack of a method to determine the spatial distributions of permeability has severely limited our ability to understand and mathematically describe complex processes within permeable media. Even the degree of variation of intrinsic permeability that might be encountered in naturally occurring permeable media is unknown. Samples with permeability variations will exhibit spatial variations in fluid velocity. Such variations may significantly affect associated physical phenomena, such as biological activity, dispersion and colloidal transport. Spatial variations in the porosity and permeability, if not taken into account, can adversely affect the determination of any associated properties, including multiphase flow functions [16]. 

Clogging of aquifers by the growth of biomass is an operational problem. The permeability of an aquifer could be reduced due to the precipitation of biomass sludges and chemicals, or due to clay dispersion. 

Controlling fluid loss loss is particularly important in the case of the expensive high density brine completion fluids. While copolymers and terpolymers of vinyl monomers such as sodium poly(2-acrylamido-2-methylpropanesulfonate-co-N,N-dimethylacrylamide-coacrylic acid) has been used (H)), hydroxyethyl cellulose is the most commonly used fluid loss additive (11). It is difficult to get most polymers to hydrate in these brines (which may contain less than 50% wt. water). The treatment of HEC particle surfaces with aldehydes such as glyoxal can delay hydration until the HEC particles are well dispersed (12). Slurries in low viscosity oils (13) and alcohols have been used to disperse HEC particles prior to their addition to high density brines. This and the use of hot brines has been found to aid HEC dissolution. Wetting agents such as sulfosuccinate diesters have been found to result in increased permeability in cores invaded by high density brines (14). 

Flow properties of macroemulsions are different from those of non-emulsified phases 19,44). When water droplets are dispersed in a non-wetting oil phase, the relative permeability of the formation to the non-wetting phase decreases. Viscous energy must be expended to deform the emulsified water droplets so that they will pass through pore throats. If viscous forces are insufficient to overcome the capillary forces which hold the water droplet within the pore body, flow channels will become blocked with persistent, non-draining water droplets. As a result, the flow of oil to the wellbore will also be blocked. 

Other experiments are planned to study the location, distribution and resuscitation of ultramicrobacteria in large three-dimensional sandpacks. Such studies will allow a more realistic approximation of reservoir conditions than the unidirectional core studies. We do not consider that the ultramicrobacteria will reach or grow in areas where residual oil is located. Selective plugging involves blocking the high permeability zones already drained of oil. We consider that the injection of ultramicrobacteria will be carried, like waterflood operations, to the areas of the strata already drained of oil and permit them to disperse through pore spaces and resuscitate in these areas. 

In case 4, the increasing pressure compresses the cake to such as extent that it actually squeezes off the flow so that as the pressure increases the flow rate decreases. This situation can be compensated for by adding a filter aid to the slurry. This is a rigid dispersed solid that forms an incompressible cake (diatomaceous earth, sand, etc.). This provides rigidity to the cake and enhances its permeability, thus increasing the filter capacity (it may seem like a paradox that adding more solids to the slurry feed actually increases the filter performance, but it works ). 

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