Water Hydraulic Permeability Research Articles

Water and water vapor permeation and solute separation through poly(n-alkyl L-glutamate) membranes

Abstract To elucidate the mechanism of water permeation, permeation of water and water vapor through a series of poly(n-alkyl L-glutamates). polymers of methyl, propyl, and butyl glutamate were studied. It was confirmed that water and water vapor permeability were almost one order higher than in cellulose acetate membrane and increased with increasing length of the side chain. The activation energies of the hydraulic permeability of water and the diffusion coefficient of water vapor are almost three times those for pure viscous flow of water. The behavior is analyzed by the free-volume concept for mass transport, and the result shows that the mechanism of water permeation involves the molecular transport of clusters of several water molecules, though the size of the cluster is extremely small compared with that in bulk viscous flow. Separation of water-soluble solute through the homogeneous polypeptide membrane was examined. Though the rejection of NaCl is not as good as in cellulose acetate membranes, th...

The contribution of solvent drag to the intestinal absorption of the basic drugs amidopyrine and antipyrine from the jejunum of the rat.

1. Jejunal loops of anaesthetized rats were perfused with hypotonic, isotonic and hypertonic buffered solutions containing 14C-labelled amidopyrine and antipyrine at neutral and at acidic pH. The blood flow of the loop was maintained at an intermediate rate (0.7–1.0 ml min−1g−1). The water net flux was determined by means of polyethylene glycol as non-absorbable marker and amounted up to ±30 μl min−1g−1. 2. A positive water net flux (directed towards the blood) increased the appearance rate of amidopyrine and antipyrine by maximally 43.8 and 49.2%, a negative water net flux (directed towards the gut lumen) diminished it by 38.8 and 35.0%. 3. The experimental data were analysed by means of a kinetic model with the water net flux as independent variable and the epithelial permeability kFD, the serosal permeability kSFS and the sieving coefficient Φ=1−σ as absorption parameters. For antipyrine independent of the pH-value of the perfusion solution kFD was 0.123, and, for amidopyrine at pH 7 and pH 3 kFD was 0.231 and 0.091, respectively. kSFS was zero indicating that in this experimental arrangement the transfer of drug molecules to the serosal side was negligible. The sieving coefficient Φ amounted to 2.30 for amidopyrine and 2.15 for antipyrine at neutral pH. At acidic pH it amounted to 0.50 for amidopyrine and 1.44 for antipyrine. The hydraulic permeability of water was identical at neutral and acidic pH. 4. The high sieving coefficient for the two drugs at neutral pH is interpreted as indicating that water and lipophilic drug molecules interact within the lipid part of the cell membrane. At acidic pH the ionized drug molecules appear to permeate the cell membrane preferentially across other (presumably more hydrophilic) areas.

Permeabilities of coagulated cellulose acetate dialysis membranes

AbstractThe diffusive flux of NaCl and the hydraulic flux of pure water through coagulated cellulose acetate membranes are examined. Coagulated cellulose acetate membranes (without densification by heat treatment or drying) possess higher permeability than what may be expected from the permeabilities of the dry polymer. Their overall hydraulic permeability (ultrafiltration rate of water) is greatly dependent upon the membrane casting conditions and the resulting asymmetry of the membrane. On the other hand, the asymmetry of a membrane does not play as great a role in the diffusive permeability of a solute. With homogeneous membranes, higher diffusive flux is always accompanied by higher hydraulic permeability. With asymmetric membranes, this is not always true. The diffusive permeability of NaCl and the hydraulic permeability of water through coagulated cellulose acetate membranes can be controlled nearly independently. Consequently, high diffusive (NaCl) permeability with low hydraulic water permeability and vice versa can be obtained by varying the casting conditions and also by partially saponifying the denser portion of the membrane.

Diffusive and hydraulic permeabilities of water in water‐swollen polymer membranes

AbstractThe diffusive permeability of water P, which relates to diffusive flux of water under a concentration gradient of water (measured by diffusion of tritiated water), and the hydraulic permeability of water K, which relates to the water flux under a hydraulic pressure gradient are defined. For the case of diffusive transport one has P = KRT/ν1, where ν1 is the molar volume of water. The relationship between P and K was investigated as a function of hydration H, i.e., the volume fraction of water in swollen polymer membranes. The following characteristic features of water permeability are revealed. (a) In the lowhydration region (H < 0.2), water permeates by diffusion even under an applied hydraulic pressure gradient and KRT/ν1 = P. (b) In the higher hydration region KRT/ν1 is greater than P, and the ratio ω = KRT/ν1P increases nearly exponentially with decrease of (1‐H)/H. Water in this region moves partly by bulk flow under an applied hydraulic pressure gradient but moves only by diffusion in the absence of a pressure gradient. (c) The dependence of log P on (1‐H)/H is nearly linear in regions of both high and low hydration but the slopes are different. The transition occurs in about the same H range where the discrepancy between P and KRT/ν1 becomes significant. Excellent agreement was found between the experimental data for P as a function of H and the theoretical prediction based on the free‐volume concept of diffusive transport in hydrated homogeneous membranes.