Water sorption dynamic

Satterfield MB, Benziger JB (2008) Non-Fickian water sorption dynamics by Nation membranes. J Phys Qiem B 112(12) 3693-3704... 

The sorption processes of ions from water in dynamic conditions were studied by using columns with diameter of 12 mm the weight of the sorbents was 1 g. 

Suzuki, M., Araki, M. and Goto, T. (1963a). Water sorption and dynamic viscoelastic properties of untreated, HCl-treated and HCHO-treated wood. Mokuzai Gakkaishi, 9(1), 11-17. 

There are many examples of second-order analyzers that are used in analytical chemistry including many hyphenated spectroscopic tools such as FTIR-TGA, IR-microscopy, as well as GC-MS, or even two-dimensional spectroscopic techniques. Another hyphenated technique that is being developed for the study of solid-state transitions in crystalline materials is dynamic vapor sorption coupled with NIR spectroscopy (DVS-NIR).26 DVS is a water sorption balance by which the weight of a sample is carefully monitored during exposure to defined temperature and humidity. It can be used to study the stability of materials, and in this case has been used to induce solid-state transitions in anhydrous theophylline. By interfacing an NIR spectrometer with a fiber-optic probe to the DVS, the transitions of the theophylline can be monitored spectroscopically. The DVS-NIR has proven to be a useful tool in the study of the solid-state transitions of theophylline. It has been used to identify a transition that exists in the conversion of the anhydrous form to the hydrate during the course of water sorption. 

Diffusion coefficients for sorbed solvent and ions in Nafion have been estimated using several techniques. Yeo and Eisenberg [53] studied the sorption of water by a dry slab of Nafion (EW 1155) and estimated the interdiffusion coefficient of water in the membrane over the temperature range 0-99 °C from the water uptake dynamics. Diffusion coefficients from these measurements increased with increasing temperature over the range (1-10) x 10 cm /s with a reported activation energy of 4.5 kcal/ mol (18.8 kJ/mol). The method used to estimate the diffusion coefficients by Yeo and Eisenberg [53] was based on the dependence of the uptake in the initial portion of the uptake curve and is probably not fully appropriate [82]). 

Water sorption-desorption isotherms can be carried out by using thermobalances. Now specific instruments allow to measure water sorption-desorption isotherms at different constant temperatures (e.g., dynamic vapor sorption instrument (DVS), Surface Measurement Systems Ltd., Monarch Beach, US). 

In the preformulation study, the comprehension of physicochemical properties regarding water-solid surface interaction is beneficial to the handling, formulation, and manufacture of the finished products. Data on sorption/de-sorption isotherm, hydration of salts of drug product, water sorption of pharmaceutical excipients, and kinetics of water adsorption or desorption of a substance can be obtained effectively by the dynamic vapor sorption method. The knowledge may be utilized for dosage form design and supports the understanding of the mechanism of action. 

The dynamic moisture adsorption isotherm is another useful tool, exemplified by the water sorption/desorption of DMP 728 zwitterion as shown in Figure 16. DSC may not be helpful unless the technique is modified by punching a tiny hole in the pneumatic sample cap, from which the moisture or solvent may escape with a narrow thermal peak. Another method is to place the sample in silicon oil on the sample pan. The thermal effect of solvent boiling out is observed in the thermograph. 

The GP technique was first applied to sorption by Karickhoff (1980), who investigated the rate-limited desorption of polynuclear aromatics from freshwater sediments. The GP technique has since been used by others to investigate sorption dynamics of sediment/water (Karickhoff and Morris, 1985 Oliver, 1985 Coates and Elzerman, 1986 Wu and Gschwend, 1986) and soil/water (Buxton and Green, 1987 Brusseau et al., 1990a) systems. To employ the GP technique, a reactor containing a headspace and a pre-... 

The water-sorption experiments were carried out in a dynamic flow vapor sorption apparatus (Model SGA100, VTI Corporation, Hialeah, FL). Samples of the two polymorphs were placed in the instrument s sample chamber and their moisture uptake as a function of relative humidity (RH) was measured. Water-sorption isotherms for both polymorphs were carried out imder the temperature conditions of 20, 25, 35, and 45°C. The amoimt of sample used for an analysis depends on the sample s tendency to pick up water. If the sample is highly hygroscopic, about 2-5 mg is sufficient for the test, but if the sample is nonhygroscopic, a larger mass is needed, about 25 mg or more. For this study, water-sorption isotherms for both polymorphs were carried out using the flow system and a sample size of about 50 mg. 

Can these results for water sorption be related to the application of fountain solution to paper during lithographic printing In Figure 16 the addition of a surfactant is seen to have little effect on the dynamic surface tension of water at a surface age of 3 ms. Thus, on the time scale of the wetting of newsprint, fountain solutions which consist principally of an aqueous solution of gum arable may behave similarly to the case of water alone. Conversely, as shown in Figure 17 fountain solutions containing isopropanol exhibit lower dynamic surface tensions and should wet paper more readily than water alone. 

Amount of ethylene immobilized in HZSM-5 catalysts was estimated from sorption and reaction dynamics as a function of reactor temperature. Space accessible in loaded crystals was measured using water sorption at 298 K. 

Let us choose a situation where a sample of a bleached kraft linerboard (240 gsm) is subjected to a ramp change in humidity from a base value of 15% to 45%. The parameters of the paper sheet are shown below in Table 5. Sorption dynamics for these sheets, the steady state diffusion coefficients for water vapor... 

A practically very useful method to investigate hydrates is dynamic vapor sorption (DVS) (see Section 8.2.3.2). It provides information on the water sorption behavior of substances, and while it is less suited than slurry experiments to obtain thermodynamic parameters of hydrates, it provides very valuable kinetic information. 

Technically, samples were periodically weighed and water sorption equihbrium was considered to be reached when no mass change occurred. Then, the water concentration in the films was calculated from the sorption data in the stated conditions. This technique is less widely used for the benefit of automated dynamic gravimetric sorption system. 

Moreover, isopiestic water sorption data and dynamic vapor sorption (Soboleva et al., 2011) provide information on water uptake as a function of relative humidity in the surrounding gas phase. This information, if combined with pore size distribution data, could help determine the wetting angle in pores or the Gibbs energy of water sorption as functions of pore size. 

The main assumptions of the simple bulk conductivity model are valid at high water contents. This wording implies that a lower characteristic value of water content exists, below which the model is invalid. This value emerges as an important membrane characteristic. It will be discussed below, based on an assessment of water sorption properties and dynamics of proton and water transport. 

The presented mechanism for PEM water sorption is consistent with thermodynamic principles, while predicting experimentally found trends correctly. Currently, full-scale molecular dynamics simulations would not be able to capture wall charge density effects and elastic effects in an ensemble of pores. 

Structure and water sorption characteristics of fuel cell media determine their transport properties. The dynamic properties of water determine microscopic transport mechanisms and diffusion rates of protons in PEM and CLs. Protons must be transported at sufficiently high rates, away from or toward the active Pt catalyst in anode and cathode catalyst layers, respectively. Effective rates of proton transport in nanoporous PEM and CLs result from a convolution of microscopic transport rates of protons with random network properties of aqueous pathways. Accounting for the geometry of these materials, namely, their external surface area and thickness, gives their resistances. 

When modeling dynamic water sorption phenomena, information about evaporation and condensation is contained in the boundary conditions that account for water exchange across membrane-gas interfaces. The rate of interfacial water exchange is determined by values of the instantaneous water content on the PEM side of the interface, Xm, and by the vapor pressure, of the adjacent gas. The deviation of these local variables from their chemical equilibrium establishes the driving force of interfacial vaporization exchange. 

FIGURE 5.3 Modeling of transient water flux data for Nation 117. (a) The relaxation of the experimental outlet vapor pressure (open circle) for Nafion 117 in LE mode at 50°C, flow chamber volume V = 0.125 L, flow rate V = 0.1 L min membrane area A = 2 cm, and saturation vapor pressure = 12336.7 Pa. Plotted for comparison are model simulations for a slow transport coefficient (dash dot), fast transport coefficient (dash), and a concentration-dependent transport coefficient (gray), (b) Water concentration profiles calculated in the model at different time. (Reprinted from Electrochem. Commun. 13, Rinaldo, S. G. et al. Vaporization exchange model for dynamic water sorption in Nafion Transient solution, 5-7, Figures 1 and 2, Copyright (2011) Elsevier. With permission.)... 

Rinaldo, S. G., Momoe, C. W., Romero, T., Merida, W., and Eikerling, M. 2011. Vaporization-exchange model for dynamic water sorption in Nafion Transient solution. Electmchen Comrmm., 13, 5-7. 

Satterfield, M. B. and Benziger, J. B. 2008. Non-Fickian water vapor sorption dynamics by Nafion membranes, 3693-3704. 

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