Water sorbed

Lahajnar, G., Zupancic, L, Rupprecht, A. Proton NMR relaxation and diffusion study of water sorbed in oriented DNA and hyaluronic acid samples. In Biophysics of Water (Franks, F., Mathias, S., eds) Wiley, New York (1982) 231-234... 

Contaminant transfer to bed sediments represents another significant transfer mechanism, especially in cases where contaminants are in the form of suspended solids or are dissolved hydrophobic substances that can become adsorbed by organic matter in bed sediments. For the purposes of this chapter, sediments and water are considered part of a single system because of their complex interassociation. Surface water-bed sediment transfer is reversible bed sediments often act as temporary repositories for contaminants and gradually rerelease contaminants to surface waters. Sorbed or settled contaminants are frequently transported with bed sediment migration or flow. Transfer of sorbed contaminants to bottomdwelling, edible biota represents a fate pathway potentially resulting in human exposure. Where this transfer mechanism appears likely, the biotic fate of contaminants should be assessed. 

The most fundamental manner of demonstrating the relationship between sorbed water vapor and a solid is the water sorption-desorption isotherm. The water sorption-desorption isotherm describes the relationship between the equilibrium amount of water vapor sorbed to a solid (usually expressed as amount per unit mass or per unit surface area of solid) and the thermodynamic quantity, water activity (aw), at constant temperature and pressure. At equilibrium the chemical potential of water sorbed to the solid must equal the chemical potential of water in the vapor phase. Water activity in the vapor phase is related to chemical potential by... 

The sorption branch of the isotherm is obtained experimentally by measuring the equilibrium amount of water sorbed to a solid at known relative pressure, beginning with a known mass of absolutely dry solid and then progressively increasing the relative pressure in the system. Drying the solid... 

In essence, volumetric methods equilibrate a known headspace dosing volume at a given (measured) water vapor pressure, and then they expose the pre-equil-ibrated sample to this water vapor, with subsequent measurement of the water vapor pressure after equilibration. The mass of water sorbed, An (in moles), at the final pressure in the system, Pf, is obtained from the difference, AP, between Pfcalc, the calculated water vapor pressure at equilibrium, and /ylleas, the final measured water vapor pressure ... 

Unfortunately, the literature is relatively sparse with examples showing the water uptake profile onto crystalline, nonhydrating substances below RHq. This is most likely due to the difficulty in accurately measuring the small amounts of water that are sorbed. Alkali halides are an exception, however, likely due to their well-characterized particle morphologies [34—37]. Figure 2 shows a water uptake isotherm onto recrystallized sodium chloride [37]. Note that the amount of water sorbed as a function of relative humidity is normalized to the specific surface area of the sample. Since water is sorbed only to the external surface of... 

Fig. 5 Net differential heat of sorption for water vapor by native potato starch at 20°C as a function of amount of water sorbed per mass of dry starch. (From Ref. 14.)...

Etch selectivity is crucial to the gas-phase functionalized resist schemes. Since the thickness of the etch resistant Ti02 layer that forms on the polymer film should depend on the amount of water sorbed on the polymer surface, we studied the influence of various processing parameters on the surface water content as measured by the amounts of Ti deposited. 

To estimate the limiting value t (i) and to introduce the molal fixed charge concentration X, expressed in equivalents of univalent fixed anions per kg of water sorbed by the membrane, we have treated the ion concentrations in the membrane as being governed by a Donnan distribution. 

Dense Membrane Studies. The weight of water sorbed by SPSF-Na membranes at 100% relative humidity is plotted as a function of time in Figure 1. Water uptake increased with Increasing D.S.. The same trend was observed for the K salt membranes. The results are summarized in Table III. The point to be noted here is that the absolute amount of water sorbed by the SPSF-Na membranes is greater (by a factor of two) than that of the SPSF-K membranes. It is clear that hydrophillcity increases with increasing D.S. and is dependent on the nature of the counter ion. 

Water Sorbed by Dense Membranes at 100% Relative Humidity and 25°C... 

The amount of water adsorbed by a solid can be expressed in a number of ways. Many investigators report the amount of water sorbed, but do not taken into account the amount of water initially in the sample. The calculation of percent moisture uptake relative to the dry weight of the sample normalizes samples to the same initial point, and makes data from various samples comparable. The percent sorbed relative to dry weight is calculated from the following ... 

With ion exchangers as catalysts for olefin hydration, special attention was paid to transport problems within the resin particles and to their effects on the reaction kinetics. In all cases, the rate was found to be of the first order with respect to the olefin. The role of water is more complicated but it is supposed that it is absorbed by the resin maintaining it in a swollen state the olefin must diffuse through the water or gel phase to a catalytic site where it may react. The quantitative interpretation depends on whether the reaction is carried out in a vapour system, liquid-vapour system or two-phase liquid system. In the vapour system [284, 285], the amount of water sorbed by the resin depends on the H20 partial pressure it was found at 125—170°C and 1.1—5.1 bar that 2-methyl-propene hydration rate is directly proportional to the amount of sorbed water... 

Water isotherms determined at 35°C. are shown in Figure 3. The amount of water sorbed by the Pittsburgh coal is about twice the amount taken up by Pocahontas coal. These isotherms represent equilibrium measurements. Hysteresis loops that do not close at relative pressures less than 0.3 are characteristic of water adsorption on coal. 

Next, let us consider the applicability of this unique wettability phenomenon. With Ti02 photocatalyst alone, this highly amphiphilic surface disappears soon after exposure of the surface to light. When the photocatalyst has been combined with a water-sorbing substance that can hold water within its structure (such as silicon dioxide or silica gel), the effect of the surface continues even in the dark. Fogging of the surfaces of mirrors and glass occurs when steam that has cooled on these surfaces form many water droplets. On a highly amphiphilic surface, no... 

Norinaga, K., Kumagai, H., Hayashi, J.-I., and Chiba,T. (1998). ClassiAcation of water sorbed in coal on the basis of congelation characteristics. Energy Fuels 12(3), 574-579. 

From the literature cited it can be concluded that about 90% of the recoverable DDT residue will reside in the top 3 inches of the soil or at cultivation or plow depth. Certain persistent insecticides can be removed from the soil through volatilization. The extent of volatilization is determined in part by the vapor pressure of the insecticide, by displacement from the soil particle by other substances, by the presence and type of cover crop, and by the "turning over of the soil. Insecticides from treated areas can enter the surface water sorbed onto eroded soil particles and/or desorbed from the soil by water. 

Fig. 19. Correlation of S in mL of water sorbed at liquid saturation per gram of Gly-MA-co-TEGDMA copolymers (prepared by Refojo [145] in 1965) with the corresponding calculated cube root of the average number of backbone carbon atoms between crosslink junctions...

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