Permeability integral

D. J., Jeffrey, P. Improving the in vitro prediction of in vivo centtal nervous system penetration Integrating permeability, P-glycoprotein efflux, and free fractions in blood and brain. 

The integral permeability coefficient P may be determined directly from permeation steady-state flux measurements or indirectly from sorption kinetic measurements 27 521 activity is usually replaced by gas concentration or pressure (unless the gas deviates substantially from ideal behaviour and it is desired to allow for this) and a<>, ax (p0, Pi) are the boundary high and low activities (pressures) respectively in a permeation experiment, or the final (initial) and initial (final) activities (pressures) respectively in an absorption (desorption) experiment. 

Fig. 8. Experimental integral permeability data for PC-C02 pure C02 O in the presence of 117.8 torr of isopentane on the upstream side (P. = 0) 71>...

Fig. 9. Experimental integral permeability plots for Dyes I—III through Nylon 6 membranes according to Eq. (14)84) (with CDS1 varying between zero and a small finite value to the extent indicated by the horizontal bars) O Dye I A Dye II Dye III...

Fig. 11. Relative integral permeability P/PB of membranes composed of copolymers of styrene (A) grafted onto a polydimethyl siloxane matrix (B) as a function of composition (volume fraction of A) O C3Hs iso-C4H10 (a) Eq. (30) (b) Eq. (31) (c) Eq. (33) (d) Eq. (32) 10,1...

Fig. 12. Relative integral permeability P/PFDMS of propane through polydimethyl siloxane (PDMS) — poly(ethylene-copropylene) rubber (EPR) blend membranes as a function of blend...

The ultrathin porous glass membranes were examined for the permeability of air at 25°C. The measurements were performed as follows The membrane was sticked on a brass plate containing a bore with 2 and 5 mm diameter, respectively. After that, the plate was fixed with a special dome on a turbo molecular pump (TMU 261, Pfeiffer). Now, the dome was evacuated. The gas flow was determined by measuring the pressure below the membrane. Finally, the integral permeability was estimated using the pumping speed, the measured pressures and the membrane thickness. 

Additionally we may conclude that low-pressure integral permeability is a quick and easy to use tool for crack (defect) detection and leads to detailed structural characterization of asymmetric membranes. Furthermore, permeability experiments give a rough but reliable measure of the maximum pore size of the structure under study. 

Parameters q and W are variables when filtration conditions are changed. Coefficient (rj, is a function of pressure (rj, = f(P). The exact relationship can be derived from experiments in a device called a compression-permeability cell. Once this relationship is defined, the integral of the right hand side of the above equation may be evaluated analytically. Or, if the relationship is in the form of a curve, the evaluation may be made graphically. The interrelation between W and P, is established by the pump characteristics, which define q = f(W) in the integral. Filtration time may then be determined from dq/dt = W, from which we may state ... 

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. 

Let us proceed with the description of the results from theory and simulation. First, consider the case of a narrow barrier, w = 0.5, and discuss the pair distribution functions (pdfs) of fluid species with respect to a matrix particle, gfm r). This pdf has been a main focus of previous statistical mechanical investigations of simple fluids in contact with an individual permeable barrier via integral equations and density functional methodology [49-52]. 

Finally, let us discuss the adsorption isotherms. The chemical potential is more difficult to evaluate adequately from integral equations than the structural properties. It appears, however, that the ROZ-PY theory reflects trends observed in simulation perfectly well. The results for the adsorption isotherms for a hard sphere fluid in permeable multiple membranes, following from the ROZ-PY theory and simulations for a matrix at p = 0.6, are shown in Fig. 4. The agreement between the theoretical results and compu-... 

M. Borowko, P. Bryk, O. Pizio, S. Sokolowski. Fluids in contact with periodic semi-permeable walls an integral equation approach. Mol Phys 94 %C1, 1998. 

In addition to the reports of uptake of intact small liposomes (SUV) by hepatocytes (Scherphof et al., 1983), there is some evidence of uptake of intravenously administered liposomes as intact structures by cells other than mononuclear phagocytes of the MPS. Recently, the integrity of the capillary endothelial barrier in several pathophysiological conditions was discussed (Bodor and Brewster, 1986). Several studies already indicated an increased capillary permeability during inflammation both in animals (Lopez-Berestein et al., 1984a) and in man (Morgan et al., 1985 Williams et al., 1987). 

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