Water permeation studies coefficient

The study of the dynamical behavior of water molecules and protons as a function of the state of hydration is of great importance for understanding the mechanisms of proton and water transport and their coupling. Such studies can rationalize the influence of the random self-organized polymer morphology and water uptake on effective physicochemical properties (i.e., proton conductivity, water permeation rates, and electro-osmotic drag coefficients). 

Experimental Studies of Water Permeation in PEMs Electro-Osmotic Drag Coefficient... 

Permeation properties are inportant for the design and implementation of polymer nanocomposites and polymer nanocomposite foam products. The literature is quite limited regarding permeation studies on these materials. In this paper, we focus on permeation properties of polystyrene nanoconposites (two types of nanoclay and carbon nanofiber) and thdr respective foams. Commercial instruments (PERMATRAN-C Model 4/41 and PERMATRAN-W Model 3/33 fi-om Mocon) were used to measure steady state permeability coefficients of CO2 and water vapor at three tenperatures lOTfC, 25TfC, and 401C. From these data permeation rates and permeation activation energy are compared based on nanocomposite morphology. 

Takamatsu et al. studied the diffusion of water into the acid as well as mono-, di-, and trivalent salt forms of 1155 and 1200 EW samples."pj e gravimetric uptakes of membranes immersed in distilled liquid water versus time were determined. Three approximate diffusion formulas were applied to the data, and all yielded essentially the same result. The log D versus 1/7 plots, over the range 20—81 °C, yielded activation energies of 4.9 and 13.0 kcal/mol for the acid and K+ forms, respectively. Diffusion coefficients of various mineral cations that permeated from aqueous electrolytes were considerably smaller than that of water. Also, log Z7was seen to be proportional to the quantity q a, where q is the charge of the cation and a is the center-to-center distance between the cation and fixed anion in a contact ion pair. 

More than a hundred years ago, Meyer and Overton made their seminal discovery on the correlation between oil/water partition coefficients and the narcotie potencies of small organic molecules (7,8). Ferguson extended this analysis by placing the relationship between depressant action and hydrophobicity in a thermodynamic context the relative saturation of the depressant in the biophase was a critical determinant of its narcotic potency (9). At this time, the success of the Hammett equation began to permeate structure-activity studies and hydrophobicity as a determinant was relegated to the background. In a landmark study, Hansch and his colleagues de-... 

Permeation-skin-gas chromatography (GC)/MS A silastic membrane was coated onto a fiber to be used as a permeation membrane. The MCF was immersed in the donor phase to partition the compounds into the membrane. At a given partition time, the MCF was transferred into a GC injector to evaporate the partitioned compounds for quantitative and qualitative analyses. This technique was developed and demonstrated to study the percutaneous permeation of a complex mixture consisting of 30 compounds. Each compound permeated into the membrane was identified and quantified with GC/MS. The standard deviation was less than 10% in 12 repeated permeation experiments. The partition coefficients and permeation rates in static and stirred donor solutions were obtained for each compound. The partition coefficients measured by this technique were well correlated (Pf — 0.93) with the reported octanol/water partition coefficients. This technique can be used to study the percutaneous permeation of chemical mixtures. No expensive radiolabeled chemicals were required. Each compound permeated into the membrane can be identified and quantified. The initial permeation rate and equilibrium time can be obtained for each compound, which could serve as characteristic parameters regarding the skin permeability of the compound. 

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