Water sorption, kinetics

Turner, D. T. (1982). Poly(methyl methacrylate) plus water. Sorption kinetics and volumetric changes. Polymer, 23, 197-202. 

Pure PHEMA gel is sufficiently physically cross-linked by entanglements that it swells in water without dissolving, even without covalent cross-links. Its water sorption kinetics are Fickian over a broad temperature range. As the temperature increases, the diffusion coefficient of the sorption process rises from a value of 3.2 X 10 8 cm2/s at 4°C to 5.6 x 10 7 cm2/s at 88°C according to an Arrhenius rate law with an activation energy of 6.1 kcal/mol. At 5°C, the sample becomes completely rubbery at 60% of the equilibrium solvent uptake (q = 1.67). This transition drops steadily as Tg is approached ( 90°C), so that at 88°C the sample becomes entirely rubbery with less than 30% of the equilibrium uptake (q = 1.51) (data cited here are from Ref. 138). 

Aramid fibers are popular in the reinforcement of various matrix materials. It is frequently the case that low water uptake by a composite is required, which cannot be regulated by the matrix. Figure 16.15 shows that aramid fibers differ in water sorption kinetics. Fiber E gives better performance due to a hydrophobic coating. This lower water sorption of the fiber decreases water sorption of the composite, as was established in the study. ... 

Figure 16.15. Water sorption kinetics of aramid fibers vs. time. [Adapted, by permission, from Rebouillat S, Escoubes M, Gauthier R, J. Adhesion Sci. Technol., 10, No.7, 1996, 635-50.]...

Bluestein, P.M. and Labuza, T.P., Water sorption kinetics in a model freeze-dried food, AIChE J., 18(4) 706 712, 1972. 

Fig. 11. Water vapour sorption kinetics in the same external conditions for as cast and hygrothermally damaged DGEBA-TETA neat resin...

Nguyen, T. H., Himmelstein, K. J., and Higuchi, T., Some equilibrium and kinetic aspects of water sorption in poly(ortho esters), Int. J. Pharm.. 25, 1-12, 1985. 

Since an understanding of the nature of water sorption by materials is of extreme interest to the formulator, an evaluation of the degree of hygroscopicity associated with a given material is crucial to the development process. A systematic approach for these types of studies has been outlined, in which the kinetics of water adsorption can be deduced [84]. This work should be performed at the preformulation stage, where the effect of water on the various components (and mixtures of these) needs to be addressed prior to any final decision as to the formulation composition [85]. It would be far better to discover any... 

Lievonen, S.M. and Roos, Y.H. 2002b. Water sorption of food models for studies of glass transition and reaction kinetics. J. Food Sci. 67, 1758-1766. 

Though this system is perhaps an extreme example of slow sorption kinetics, it illustrates that the assumption of rapid equilibrium between the sediment and aqueous phases is questionable. The importance of such an observation to the investigation of hydrolysis kinetics in sediment/water systems must be emphasized. Certainly, any model of hydrolysis kinetics in sediment/water systems must include explicit expressions for the kinetics of the sorption/desorption process. 

Bottleneck Boundary Around a Spherical Structure Sorption Kinetics for Porous Particles Surrounded by Water Box 19.3 Spherical Wall Boundary with Boundary Layer Finite Bath Sorption... 

Sorption Kinetics for Porous Particles Surrounded by Water... 

Next we analyze the sorption kinetics of a sorbate with constant aqueous concentration, C°, sorbing into a porous spherical aggregate with radius rQ. More precisely, the macroparticle is a homogeneous aggregate of microparticles which are separated by micropores filled with water (Fig. 19.17). The sorbate diffuses in these pores and sorbs to the microparticles. It is not relevant whether sorption occurs at the surface or in the interior of the microparticles as long as we can assume that sorption equilibrium between the solute concentration and the microparticles at each position within the aggregate is attained instantaneously. 

Wu, S.-C., and P. M. Gschwend, Numerical modeling of sorption kinetics of organic compounds to soil and sediment particles , Water Resources Res., 24, 1373-1383 (1988). 

The addition of a filler changes the kinetics of the water absorption by an epoxy binder, water absorption becoming a multistage process (Fig. 12). Crank and Park150) have given the equation for the kinetics of water sorption by a thin plate, as well as a solution of the Fickian diffusion differential Equation as ... 

Pignatello, J. J. 1993. Recent advances in sorption kinetics. In Organic Substances in Soil and Water Natural Constituents and Their Influences on Contaminant Behavior (A. J. Beck, K. C. Jones, M. H. B. Hayes, and U. Mingelgrin, Eds.), pp. 128-140. Royal Society of Chemistry, Cambridge, UK. 

Figure 6.7. Phenanthrene sorption kinetics on a sediment, where p is the sediment/water ratio, P is the solution-phase pollutant concentration, and Pe is the equilibrium solution-phase concentration of the pollutant. [From Karickhoff (1980), with permission.]...

Additives to starch exert varying effects on the kinetics of water sorption. For example, lipids do not significantly affect the content of adsorbed water. The mode of starch defatting can also influence moisture sorption by molecules of the defatting solvent occupying active centers of sorption.389 The addition of either sucrose or lipids to starch has the same effect on both branches of the hysteresis curve.386,398 Some additives, such as dimethyl sulfoxide or ammonium rhodanide, induce selectivity of the adsorption and solvation of starch 411 Sulfur dioxide accelerates water sorption regardless of the temperature.412 Pretreatment of starch with sulfur dioxide usually increases the water sorption.413 Studies on the sorption of components of water-alcohol mixtures are discussed in Section IV. 

Figure 9. Dissolved arsenate and monomethyl arsonic acid (MMAA) concentrations in pore waters of sediments spiked with MMAA and predictions of sorption/ kinetic model. Model parameters k = 0.07 day, T o mmaa = 4.5 fxmol g, Kmmaa = 5.0 fxmol L Tcc,AsOi = 3.5 fxmol g Ka. o, = 5.0 fxmol L k (a) Inorganic arsenic, measured (b) arsenate, predicted (c) MMAA, measured (d) MMAA, predicted.

Sorption of monomethyl arsonic acid (MMAA), dimethyl arsinic acid (DMAA), and arsenate on anaerobic bottom sediments from the Menominee River, Wisconsin are described by Langmuir Isotherms. These results were Incorporated Into a kinetic model of arsenic species transforamtlon which takes sorption Into account. Model predictions were found to be sensitive to the sediment water content and r, the adsorptive capacity of the sediment. Demethylatlon of MMAA and DMAA was observed In sediment Incubation experiments. The predictions of the sorption/kinetic model were In good agreement with the results of the Incubation experiments. 

Finally, the critical relative humidities are dependent on the nature of the solid. For example, the spontaneous dissolution process has been observed for many water-soluble substances at relative humidities significantly below that associated with a saturated solution of the substance in water.Van Campen, Amidon, and Zograf have examined the moisture sorption kinetics of deliquescent solids at relative humidities above what they term the critical relative humidity (RHo), where adsorbed water takes on the character of condensed water and serves as a solvent. It is important to recognize that a highly undesirable process such as deliquescence can occur when it may not be expected (e.g., when RHo < RH < RHs). 

Figure 6. Kinetics of water sorption mass action kinetics in terms of Equation 7 water rate analysis...

Gentry et al. (1976) have recently shown, on the basis of isotopic analyses, that uranium introduction may have occurred far more recently than was previously supposed. However, they find also that, in some instances, the uranium was introduced before coalification was complete since the haloes have been compressed with the coal as it increased in rank. These results are consistent with laboratory and field work by Szalay (1964) who showed that the insoluble humic acids in peat are capable of concentrating uranium from very dilute solutions in natural waters. Sorption occurs as uranyl humate , the process following the normal kinetics of the Langmuir adsorption equation. (Where uraninite occurs in association with peat or other carbonaceous matter, the uranium may thus have been initially sorbed as a uranyl compound which was later reduced to uraninite.)... 

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