Water vapor sorption isotherm

Fig. 6 Water vapor sorption isotherms for poly(vinylpyrrolidone) at 60°C(+) 30°C (x) -20°C ( ) and -40°C (A). Data were taken from Oksanen and Zografi [71,75]. A 0 represents the calculated water contents necessary to depress Tg to the temperature of the isotherms.

Mauritz and Rogers constructed a water vapor sorption isotherm model for ionomers with inherently clustered morphologies, as applied to Nafion mono-... 

Water vapor adsorption isotherms have been obtained on cotton from room temperature up to 150°C [303,304]. Theoretical models for explaining the water vapor sorption isotherms of cellulose have been reviewed [303]. Only adsorption theories will be discussed here at ambient temperatures. The shape of the isotherm indicates that multilayer adsorption occurs and thus the Brunauer, Emmett and Teller (BET) or the Guggenheim, Anderson and deBoer (GAB) theory can be applied. In fact, the BET equation can only be applied at relative vapor pressures (RVPs) below 0.5 and after modification up to a RVP of 0.8 [305]. The GAB equation, which was not discussed in the chapter in the book Cellulose Chemistry and Its Applications [303], can be applied up to RVPs above 0.9 [306]. Initially as the RVP... 

Figure 6. Equilibrium water vapor sorption isotherms obtained on female stratum corneum (age 29) using salt solutions ( ) and the dynamic method (O) at 23.3 0.5°C...

Fig. 6 Water vapor sorption isotherm for crystalline and amorphous samples of indomethacin. ( ) Amorphous ( ) crystalline. (From Ref. " l)...

The three natural CDs form crystalline structures in the solid state that decompose above 200°C with no definite melting points. They are not considered hygroscopic, but they do form various stable hydrates. The water vapor sorption isotherms (Fig. 9) show two phases for the p- and y-CDs, and one phase for a-CD. At 11% RH, ot-CD absorbs 4 water molecules and upon long-term storage, forms a stable hydrate with 6 water molecules. The water content gradually increases with increasing humidity to a constant value of 6.6 water molecules per CD molecrJe at and above 79 /o Four different... 

Fig. 9 Water vapor sorption isotherms for a-, P-, and y-CD at 40 C. (Dashed line adsorption, solid line desorption). (Adapted from Ref...

Water Sorption. The water vapor sorption isotherm (293 K) is given in Figure 3. The general sigmoidal shape is evident, and the hysteretic phenomenon is quite pronounced, even when desorption is instigated from intermediate pressures (about 0.6 Pq), and vacuum closure... 

The data for the crystal structure, NMR structure, powder x-ray diffraction pattern, water vapor sorption isotherms, glass transition temperature as a function of water, heat capacity, heat of solution properties, vapor pressure, and osmotic pressure are described in the literature. 

Base on minimum RH for stable hydrate form at different temperature (from water vapor sorption isotherms)... 

Water vapor sorption Isothermal microcalorimetry Intrinsic dissolution Triboelectric property... 

H. D. Orchiston, Adsorption of water vapor. I Soils at 25 C, Soil Sci. 76 453 (1953). J. P. Quirk, Significance of surface areas calculated from water vapor sorption isotherms by use of the BET equation. Soil Sci. 80 423 (1955). 

FIG U RE 1.21 Water vapor sorption isotherms on polyvinyledene chloride (PVDC and urea formaldehyde resin (UF) carbons before and after outgassing and oxidation. (From Bansal, R.C., Dhami, T.L., and Prakash, S., Carbon, 16, 389, 1978. With permission.)... 

FIGURE 6 Water vapor sorption isotherms on smectites exchanged with Ca, Ba, Cs, and Na ions. (Adapted from Ref. 89.)... 

The conventional approach to perform water vapor sorption kinetics is based on the measnrement of the film sample mass until reaching constant value corresponding to a saturation level in a hydrated environment. For each hydrated enviromnent, the mass of sample is measured allowing to obtain the mass gain, ejqtressed in percent, or, in other word, the water concentration, expressed in mass of water soibed per mass of polymer or in mmol of water soibed per mass of polymer, inside sample. The combination of mass gain at each humidity level leads to build the water vapor sorption isotherm. The water vapor sorption and the isotherm shape are depending on the moisture resistance of polymer and its ability to interact with water. 

Figure 14.1 Equilibrium water vapor sorption isotherms versus activity at 40°C.

Figure 1. Water-vapor sorption isotherms for a lithium kaolinite. (From R. T. Martin [1958], Water vapor sorption on lithium kaolinite, Clays Clay Min, Proc. 5th Natl. Conf., Pub. 566, Natl. Acad. Sci.-Natl. Res. Coun., Washington D.C., pp. 23-38 (Figure 3).)...

Information on the free energy, heat, and entropy of water adsorption on clays during the subsequent stages of the adsorption and desorption process can be calculated from water-vapor sorption isotherms obtained at different temperatures. Alternatively, these quantities can be determined by combining the data of a single isotherm with data for the heats of adsorption obtained directly. In appropriate calorimeters, one can measure the heat of adsorption of increments of vapor admitted to the sample, or one can measure the heats of immersion of samples that are previously equilibrated with water vapor at various relative vapor pressures. The heat of desorption can also be obtained from the peak areas of differential thermal analysis curves of partially and completely hydrated samples (Barshad [1952]). 

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