Saturation plateau

Values of apparent surface area can be derived only if the solute isotherm exhibits a long saturation plateau. Unfortunately, the derived values are often of questionable significance since the exact structure of the monolayer (containing both solute and solvent) is rarely known. The study of microporosity by adsorption from solution measurements is in its infancy, but the use of comparison plots appears to be a promising approach. 

We studied the NaY/toluene system at 150°C and for high partial pressure of toluene Pcov> 0 Pa) corresponding to saturation temperatures (Tj) higher than -40°C. The adsorption isotherm and the experimental heats of adsorption are shown on Fig. 2 and 3. Such data correspond to the end of the Henry area and to the saturation plateau of the isotherm. The average isosteric heat calculated for a coverage ratio of 2.081 mmol/g is 97.8 kJ/mol. In this area it is possible to compare our values to existing data. The discrepancies appear to be less than 5% on the adsorption isotherm. We provide a first result in the Henry area IPa)... 

Pores with different sizes show characteristic physical adsorption effects as manifested in the isotherm. The isotherm shows the relationship between the amount of a given gas taken up or released by a solid as a function of the gas pressure under a constant temperature. The type-I isotherm shows a steep increase at very low pressures and a long saturation plateau and is characteristic of microporous materials. The type-IV isotherm exhibits a steep increase at high relative pressure and, in many cases, a hysteresis loop, which is associated with capillary condensation in mesopores. 

The NH2 groups affect the amount of adsorbed CO2 as well as the thermal behavior and illustrate the change of thermodynamics with composition. At higher pressures (not displayed in Figure 49.10), the amino-modified adsorbents show a saturation plateau around 5 bar CO2 and a load of about 5-10 wt% CO2, depending weakly on the surface area, whereas the CHa-modified material... 

Reconstitute the protein to be tested to 8.96 mg/mL in equilibration buffer and load the solution continuously onto the column until an A g saturation plateau is achieved ((ProteinFig. 5). 

Segregation of a poly(2-vinylpyrrolidone- /oc -styrene-c/8- /oc -2-vinylpyrrolidone) (PVP-dPS-PVP) triblock and dPS-PVP diblock copol5miers between the PS and PVP homopolymers was studied by Dai and co-workers (169). Both the block copolymers show an increase in the interfacial excess beyond the saturation plateau, due to condensation of copolymer micelles adjacent to the PS/PVP interface in the PS phase (Fig. 9). A significantly lower critical micelle condensation (CMC) was determined for the triblock copolymer when compared with the diblock. While the condensation of the diblock copolymer micelles at the PS/PVP surface occurs above the CMC, no such preferential segregation is observed for the triblock copolymer. 

Similar to UDS, Aerosol OT adsorbs strongly to alumina, showing an adsorbed amount of 5 jxmol/m at the saturation plateau. This is close to the 8 p,mol/m recorded in the previous case (i.e., LiDS adsorption on alumina). 

Isotherms of type 1 exhibit a saturation plateau due to adsorption of an inert sorbate on the surface of pores. In this case. 

The sorption isotherms of the vapor of -hexane by cotton cellulose (COC) and viscose fibers (VI were similar to F-shape isotherms of type 1 having the saturation plateau (Fig. 7.31). Despite lower degree of amorphicity, COC-sample had increased sorption value than the more amorphous VF-sample. This provides evidence that just surface adsorption occurs in the cellulose-hexane system. 

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