Vapour sorption

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

Pigna M, Colombo C, Violante A (2003) Competitive sorption of arsenate and phosphate on synthetic hematites (in Italian). Proceedings XXI Congress of Societa Italiana Chimica Agraria SICA (Ancona), pp 70-76 Quirk JP (1955) Significance of surface area calculated from water vapour sorption isotherms by use of the B. E. T. equation. Soil Sci 80 423-430 Rancourt DG, Fortin D, Pichler T, Lamarche G (2001) Mineralogical characterization of a natural As-rich hydrous ferric oxide coprecipitate formed by mining hydrothermal fluids and seawater. Am Mineral 86 834-851 Raven K, Jain A, Loeppert, RH (1998) Arsenite and arsenate adsorption on ferrihydrite kinetics, equilibrium, and adsorption envelopes. Environ Sci Technol 32 344-349... 

Cross, G. H. Ren, Y. Swann, M. J., Refractometric discrimination of void space filling and swelling during vapour sorption in polymer films, Analyst 2000, 125, 2173 2175... 

Mathlouthi, M. and Roge, B. 2003. Water vapour sorption isotherms and the caking of food powders. Food Chem. 82, 61-71. 

In Differential vapour sorption a sample of material is placed on an accurate balance in a temperature controlled environment where the humidity of the gas phase can be accurately controlled. The adsorption and desorption behaviour of the sample is quantified with respect to water and hysteresis phenomena are identified. 

Martins and Banks (1991) modified pine and wood samples with phenyl or butyl isocyanate and investigated the water vapour sorption properties of the modified wood. Modification resulted in a reduction in EMC at a given RH up to about 35 % WPG with butyl isocyanate, although reaction with phenyl isocyanate above 25 % WPG resulted in an increase in sorption due to cell wall damage caused by the reaction. The butyl derivative was more effective at reducing hygroscopicity over all the WPGs studied. 

Masking of some of the cell wall hydroxyl content occurs, which can be a contributory factor in reducing water vapour sorption. The efficiency of OH masking depends upon the efficiency of diffusion of the cell waU bulking agent. 

Popper, R. and Bariska, M. (1973). Acylation of wood. Part II Thermodynamics of water vapour sorption. Holz als Roh- und Werkstoff, 31(2), 65-70. 

High-energy processes (milling, lyophilisation, granulating, drying) can introduce certain amounts of amorphicity into otherwise highly crystalline material [20]. As has been previously indicated, enhanced levels of amorphicity lead to increased local levels of moismre, and increased chemical reactivity in these areas. Hancock and Zografi [49] reported on the impact of a roller-compaction process on the water vapour sorption of a sample of aspirin. They speculated that... 

Figure 7.13 Water vapour sorption by whey protein concentrate (A), dialysed whey protein concentrate (B) and dialysate (lactose) from whey protein concentrate (C) (from Kinsella and...

The most versatile surface characterisation methods are based on gas or vapour sorption and these techniques can provide physico-chemical information such as enthalpies, surface energies and diffusion constants but also surface area and pore size distributions. 

Vora, K.L. Buckton, G. Clapham, D., The use of dynamic vapour sorption and near infrared spectroscopy (DVS-NIR) to study the crystal transitions of theophylline and the report of a new solid-state transition Eur. J. Pharm. Sci. 2004, 22, 97-105. 

Hancock BC, Shamblin SL. Water vapour sorption by pharmaceutical sugars. Pharm Sci Tech Today 1998 1(8) 345-351. 

Enhancement of a flexible PVC-silica composite interface was studied by the application of gamma-aminopropyltrimethoxysilane on silane. Composites containing silica and silanised silica up to 25.6 phr and prepared by sol-gel technology were subjected to water and water vapour attacks similar to that in their daily use. Silane application resulted in diminishing liquid water and water vapour sorption by about 24.0% and 11.9%, respectively. Inhibition of dioctyl phthalate migration from composites by silane application was also determined as 24% using UV measurements. 20 refs. TURKEY... 

Structure of the material by a model based largely on evidence from total and non-evaporable water contents and water vapour sorption isotherms. Powers later modified the model in minor respects (P34). 

The content of non-evaporable water, relative to that in a fully hydrated paste of the same cement, was used as a measure of the degree of hydration. Portland cement paste takes up additional water during wet curing, so that its total water content in a saturated, surface dry condition exceeds the initial w/c ratio. Evidence from water vapour sorption isotherms indicated that the properties of the hydration product that were treated by the model were substantially independent of w/c and degree of hydration, and only slightly dependent on the characteristics of the individual cement. The hydration product was thus considered to have a fixed content of non-evaporable water and a fixed volume fraction, around 0.28, of gel pores. 

The hydration product occupies more space than the cement from which it is formed, and the capillary pores were regarded as the remnants of the initially water-filled space. Their volume thus decreases, and that of the gel pores increases, as hydration proceeds. Evidence from water vapour sorption isotherms indicated that the hydration product was composed of solid units having a size of about 14 nm, with gel pores some 2 nm across (P34). The width of the capillary pores could not be determined from the available data, but they were considered to be generally much wider than the gel pores, though tending to become narrower as the water-filled space was used up, and thus in some regions indistinguishable from gel pores. 

Brunauer and co-workers (B55,BI08) considered that the gel particles of the Powers-Brownyard model consisted of either two or three layers of C S-H, which could roll into fibres. D-drying caused irreversible loss of interlayer water, and the specific surface area could be calculated from water vapour sorption isotherms, which gave values in the region of 200m g for cement paste. Sorption isotherms using N2 give lower values of the specific surface area this was attributed to failure of this sorbate to enter all the pore spaces. 

The method has been used to study the thermodynamics of various polymer blends The results of vapour sorption have been compared with I.G.C. for PVC, polystyrene, and polyfmethyl methacrylate) with various solvents and the interaction parameters have been found to agree within experimental error... 

The evolution in calorimetry technology has also led to the development of protocols for quantitative analysis (Buckton and Darcy 1999). Fiebich and Mutz (1999) determined the amorphous content of desferal using both isothermal microcalorimetry and water vapour sorption gravimetry with a level of detection of less than 1 per cent amorphous material. The heat capacity jump associated with the glass transition of amorphous materials MTDSC was used to quantify the amorphous content of a micronised drag substance with a limit of detection of 3 per cent w/w of amorphous... 

The alteration in the porous structure of the wood cell wall as a result of the inqrregnation and toe ageing procedures, as well as after toe action of fungi (Coniophora puteana and Lentinus lepideus) was investigated by the water vapours sorption method. 

Changes in the structure and hydrophilic properties of the wood cell wall m specimens after the impregnation and ageing procedures samples were studied by the water vapours sorption method. The sorption-desoqjtion isotherms measured on a vacuum sorption balance at 295 K were analysed by the comparative method in combination with the BET method (8). The accessible specific area A (m /g), reflecting swelling capacity, the mass hydrophilicity a (mM/g) and the surface concentration of Ihc hydrophilic centres a (groups/nm ) was determined. 

Some isotherms of water vapours sorption-desorption are presented in Fig, 1. In the first cycle of sorption, the isotherms have a pronounced stepwise character, and the values of water vapour sorption are unusually low for wood specimens. This is connected with the strict drying conditions of the specimens 378K at a rapid rise in temperature) after the exposure procedure, which resulted in the fixation of the nonequilibrium structure. After saturation with water vapours and the subsequent vacuum treatment at 295K during the procedure of the sorption experiment, the second cycle of isotherms was carried out, and this state was regarded as an equilibrium one. Thus, the analysis of the specimens structure was performed on the basis of the sorption-desorption isotherms of the second cycle. 

Fig I [sotherms of water vapours sorption-desorption at 295K on pine wood after the procedure A - water (EN 113) B - oil (EN 113) ... 

Fig. 4 presents isotherms for water vapour sorption by a fibrous exchanger in different ionic forms used in the present paper. The obtained consequence of bydrophility is OH > COg" > HCOg > SOg . A sufficiently high moisture... 

Fig. 4. Isotherms of water vapour sorption a fibrous anion exchanger. Ionic forms 1 — OH...

Equation 5.4 is the basis of a more detailed and fundamental study of the swelling process achieved through the study of resin-water vapour sorption isotherms obtained isopiestically i.e. at equal total pressures and equal resin water content). The isopiestic vapour pressure technique takes account of variable activity of the water in the resin (and therefore IT) by allowing the resin to come to equilibrium with water vapour at different partial vapour pressures P. It is assumed that two resins of the same structural type, but with different degrees of crosslinking, have the same water activity at the same equivalent water content. At equilibrium between resin and vapour phases the water activity in resins (1) and (2) are given by ... 

Water vapour sorption isotherms for a 10% crosslinked sulfonic acid cation exchanger and a 0.4% crosslinked reference resin are shown in Figure 5.2 together with a calculation of the swelling pressure. The anomalous relative positions of the curves at low values of relative humidity P/Pq may be explained in terms of van der Waals type intramolecular forces which weakly bind adjacent polymer chains in de-swollen exchangers of low crosslinking. 

Figure 5.2 Water vapour sorption isotherms and calculation of swelling pressure (Reprinted with permission from B. R. Sundheim, M. H. Waxman, and H. P. Gregor, Phys. Chem., 1953, 57, 974. 1953 American Chemical Society)...

This simple relationship was derived before as equation 5.24, and was first used by Bauman and Eichorn in 1947 to predict selectivity sequences for simple monovalent cations from mean ionic activity coefficient data for pure aqueous electrolyte solutions containing a common anion. The inaccessibility of resin phase activity coefficients to direct measurement always remains a problem with thermodynamic equilibrium treatments. Therefore Glueckauf and others developed weight swelling and isopiestic water vapour sorption techniques to determine osmotic coefficients of pure salt forms of a resin, from which the mean ionic activity coefficients of mixed resinates could be computed using a modified form of Harned s Rule. Such studies predicted selectivity coefficient values which were in fair agreement with experiment and also demonstrated the fixed ion of the resin to be osmotically inactive. 

Hancock BC, Dalton CR. Effect of temperature on water vapour sorption by some amorphous pharmaceutical sugars. Pharm Dev Technol 1999 4(1) 125-131. 

The storage stability of dried products depends on a number of material characteristics. The water vapour sorption behaviour plays an important role [61]. It is characterized by sorption isotherms, which are typical for every material. The review article by Wolf and Jung [61] provides abundant references, also on a number of herbs. 

Sorensson C, Nepveu G and Kimberley M (2004) Intra- and inter-tree modelling of wood stiffness of clears of age-10 radiata pine clones, and simulated response of stiffness to increased genetic selection intensity. Connection between silviculture and wood quahty through modelling, Harrison Hot Springs, British Colombia (2002). lUFRO, 104-17 Spalt HA (1958) The fundamentals of water vapour sorption by wood. Forest Products Journal, 5(10) 288-95... 

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