Equilibrium water saturation

The equilibrium water saturation of a polymeric system increases with the number of polar groups present in the polymeric matrix. Circumstances like the accessibility of the polar groups, the relative strength of the water-water versus water-polymer bonds and for semi-crystalline polymers the degree of crystallinity, hamper a straightforward correlation between the number of polar groups and the solubility. Van Krevelen [1] presents the amount of water per structural group at equilibrium (expressed as molar ratio), as what he calls the best possible approach to the sorptive capacity of (amorphous) polymers versus water. 

Nine sample strips (about 100x10x0.1 mm) of the polymers listed in Table 7.10 were first dried at 50°C in vacuum until constant sample weights were reached. The dry samples were stored subsequently for more than two years in ion-free water (in the dark) at 20 1°C. Then the weight increase due to water absorption was measured on surface-dry samples. The samples and the equilibrium water saturation values measured are listed in Table 7.10. 

Table 7.10 The equilibrium water saturation values measured a ter more than two years of water immersion.

The maximum equilibrium water saturation of a cured epoxy system (resin system A/HHPA, see 7.2.3) was calculated succesfully using these new molar water content values. As repeating unit was recognised for this three dimensional network structure (see 7.2.4) ... 

The equilibrium water saturation measured of this epoxy resin casting sample was 0.90 %wt. Using the molar water content values reported by Van Krevelen ((1], Table 18.11 page 572), an equilibrium water concentration of 2.4 %wt. is calculated. 

The calculated equilibrium water saturation of 1.23 %wt. holds for completely amorphous PK copolymer i.e. if x(c) > 0.63, the equilibrium water saturation value of the semi-crystalline polymer as such, becomes 0.50 %wt. The equilibrium water saturation, measured on sheet material in demineralised water at 20°C, was 2.55 %wt. The calculated water saturation depends in this case mainly on the molar water content value of the CO group used. The calculated value is about five times too low and this illustrates again the necessity of looking for better defined molar water content values. 

The film sample investigated proved to be a semi-crystalline polymer system with a DSC Tg(onset)-value of 16°C. The DSC Tm(l)-value was 146°C with a Hf(l)-value of 18 J/g. The so-called processing-window of this polymer proved to be about 50°C, from 150°C to about 200°C. This bio-polymer proved to be (as usual) strongly moisture dependent. The equilibrium water saturation of the film in contact with water was 64 %wt., however visual detectable swellings effects were not noticed. 

Newsham, K. E. Rushing, J. A. 2002. Laboratory and field observations of an apparent sub capillary-equilibrium water saturation distribution in a tight gas sand reservoir. In Proceedings, 2002 Gas Technology Symposium Society of Petroleum Engineers. 

It is necessary to draw attention to the variable pH of water which may be encountered in quantitative analysis. Water in equilibrium with the normal atmosphere which contains 0.03 per cent by volume of carbon dioxide has a pH of about 5.7 very carefully prepared conductivity water has a pH close to 7 water saturated with carbon dioxide under a pressure of one atmosphere has a pH of about 3.7 at 25 °C. The analyst may therefore be dealing, according to the conditions that prevail in the laboratory, with water having a pH between the two extremes pH 3.7 and pH 7. Hence for indicators which show their alkaline colours at pH values above 4.5, the effect of carbon dioxide introduced during a titration, either from the atmosphere or from the titrating solutions, must be seriously considered. This subject is discussed again later (Section 10.12). 

The hemiacetal 54 adsorbed on water-saturated silica gel gives, by MW irradiation, a 1 1 mixture of cycloadducts isolated as silyl derivatives 55 and 56. The water is probably necessary for the success of the reaction because (i) it is an efficient generator of heat in the MW process, (ii) it accelerates the cycloaddition by hydrophobic effect, and (iii) it facilitates the hemiacetal-hydroxyketone equilibrium which furnishes the dienophile moiety for the cycloaddition [42]. 

Parker and Lenhard (1989) and Lenhard and Parker (1988) have developed equations that relate the apparent product thickness measured at a well under equilibrium conditions with the product and water saturations in a vertical column of soils adjacent to the well. By integrating the product saturation curve with respect to elevation, an equivalent depth of LNAPL-saturated pores is obtained. This process has been implemented in a computer program called OILEQUIL. The result is reported as a total oil depth in a vertical profile. The water and oil saturation curves with elevation can also be produced and printed in graphical or tabular form. 

A realistic boundary condition must account for the solubility of the gas in the mucus layer. Because ambient and most experimental concentrations of pollutant gases are very low, Henry s law (y Hx) can be used to relate the gas- and liquid-phase concentrations of the pollutant gas at equilibrium. Here y is the partial pressure of the pollutant in the gas phase expressed as a mole fraction at a total pressure of 1 atm x is the mole fraction of absorbed gas in the liquid and H is the Henry s law constant. Gases with high solubilities have low H value. When experimental data for solubility in lung fluid are unavailable, the Henry s law constant for the gas in water at 37 C can be used (see Table 7-1). Gas-absorption experiments in airway models lined with water-saturated filter paper gave results for the general sites of uptake of sulfur dioxide... 

X moisture content in equilibrium with saturated vapour pressure of water... 

Prior to a discussion on the impact of processing air dew point and temperature on the drying rate behavior of a product, it is necessary to consider heat and mass transfer. Water will move from the granule to air in an attempt to reach an equilibrium, or saturated condition, determined by thermodynamics, which can be read from a phase diagram or psychrometric chart. The rate at which water will move from liquid in the granule to vapor in the air increases the further away the system is from equilibrium. When the water evaporates, it requires an amount of energy, the heat of vaporization, in order to change from liquid to vapor. Because of this, we must also consider transfer of heat as well as movement of material. These concepts can be described by equations shown in Table 5. 

Vapor-liquid equilibrium data at atmospheric pressure (690-700 mmHg) for the systems consisting of ethyl alcohol-water saturated with copper(II) chloride, strontium chloride, and nickel(II) chloride are presented. Also provided are the solubilities of each of these salts in the liquid binary mixture at the boiling point. Copper(II) chloride and nickel(II) chloride completely break the azeotrope, while strontium chloride moves the azeotrope up to richer compositions in ethyl alcohol. The equilibrium data are correlated by two separate methods, one based on modified mole fractions, and the other on deviations from Raoult s Law. 

Fig. 2. Logarithmic activity diagram depicting equilibrium phase relations among aluminosilicates and sea water in an idealized nine-component model of tire ocean system at the noted temperatures, one atmosphere total pressure, and unit activity of H20. The shaded area represents (lie composition range of sea water at the specified temperature, and the dot-dash lines indicate the composition of sea water saturated with quartz, amotphous silica, and sepiolite, respectively. The scale to the left of the diagram refers to calcite saturation foi different fugacities of CO2. The dashed contours designate the composition (in % illite) of a mixed-layer illitcmontmorillonitc solid solution phase in equilibrium with sea water (from Helgesun, H, C. and Mackenzie, F T.. 1970. Silicate-sea water equilibria in the ocean system Deep Sea Res.).

The in-place density (bank density) of coal is the means by which coal in the seam can be expressed as tons per acre per foot of seam thickness and/or tons per square mile per foot of seam thickness (Table 6.4). The in-place density must be determined on water-saturated samples (Berkowitz, 1979) to accommodate the equilibrium moisture (Chapter 3) that exists under the in-place (or seam) conditions. 

The method of standard porosimetry (MSP)41-43 was one of the first approaches used to obtain air-water capillary pressure curves for GDMs.16 In this test, a GDM sample is initially saturated with water and contacted with a water-saturated porous disc, which is a standard with known Pc(Sw) behavior. The capillary pressure of the sample-standard system is varied by allowing the liquid to evaporate from the standard and sample while in contact. If the two media can be assumed to be in capillary equilibrium, their capillary pressures are equal. Saturation is determined by measuring the weights of the sample and standard periodically. The capillary pressure of the system is found by reference to the known capillary pressure curve of the standard. This method is limited to scanning... 

Gallagher et al.50 have reported a method that is somewhat similar to MSP. As with MSP, the GDM is initially saturated with water and placed on a porous plate that is also water-saturated. Instead of changing the GDM saturation by drying, as in MSP, the capillary pressure is controlled directly by applying suction to the porous plate. Capillary equilibrium is established between the GDM and the plate as water flows from the GDM into the plate and vice versa. 

Most of these aspects of water-sorption equilibrium correspond to the equality of chemical potentials of water in the medium and in the polymer. The consequences of this principle are illustrated by the experiment of Fig. 14.2, where an interface is created between water and a nonmiscible liquid (oil, hydrocarbon, etc.), and a polymer sample is immersed into the organic liquid. It can be observed that, despite the hydrophobic character of the surrounding medium, the sample reaches the same level of water saturation as in direct water immersion or in a saturated atmosphere. What controls the water concentration in the polymer is the ratio C/Cs of water concentrations in the organic phase, where Cs is the equilibrium concentration, which can be very low but not zero. In other words, hydrophobic surface treatments can delay the time to reach sorption equilibrium but they cannot avoid the water absorption by the substrate. 

The distribution (or partition) coefficient, Ka, of a metal cation between an aqueous (aq) and organic (org) phase may also be used to assess the selectivity of a given host for a range of metal cations under standard conditions, using the equilibrium constants (K) for the following processes (Equations 1.17-1.20) (for metal picrate (Pic) salt, water (aq) and water-saturated chloroform (org) phases, 25 °C). 

The vapor pressure of water at 80°C is 355 torr. A 100-mL vessel contained water-saturated oxygen at 80°C, the total gas pressure being 760 torr. The contents of the vessel were pumped into a 50-mL vessel at the same temperature. Assuming no condensation, (a) What were the partial pressures of oxygen and of the water vapor (b) What was the total pressure in the final equilibrium state ... 

Briggs and Shantz defined an upper limit of hygroscopic moisture which is determinable by experiment. If a soil is placed in a water-saturated atmosphere, it will absorb water vapor until a condition of approximate equilibrium is reached. The moisture content of a soil under these conditions is called the1 hygroscopic coefficient of that soil. Determination of the hygroscopic coefficient is subject to error unless carried out with considerable care. It has been pointed out that hygroscopic moisture is tenacious and difficult to drive off even at elevated temperatures. For this reason, and also because the equilibrium... 

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