Relative adsorption

There is no reason why the distortion parameter should not contain an entropy as well as an energy component, and one may therefore write 0 = 0q-sT. The entropy of adsorption, relative to bulk liquid, becomes A5fi = sexp(-ca). A critical temperature is now implied, Tc = 0o/s, at which the contact angle goes to zero [151]. For example, Tc was calculated to be 174°C by fitting adsorption and contact angle data for the -octane-PTFE system. 

Fig. XVII-23. (a) Entropy enthalpy, and free energy of adsorption relative to the liquid state of N2 on Graphon at 78.3 K (From Ref. 89.) b) Differential entropies of adsorption of n-hexane on (1) 1700°C heat-treated Spheron 6, (2) 2800°C heat-treated, (3) 3000°C heat-treated, and (4) Sterling MT-1, 3100°C heat-treated. (From Ref 18.)...

In Fig. 5.21, from Dawson s paper, the uptake at X for the 250°C-outgassed sample is dose to the calculated value for a monolayer of water with a (H20) = 101 A. Point X has therefore been ascribed to a close-packed monolayer of water on a hydroxylated surface of rutile. The fact that the differential entropy of adsorption relative to the liquid state (calculated from the isosteric heat of adsorption) changes sharply from negative to positive values in this region with A s 0 at X was regarded as supporting evidence. ... 

In order to be able to evaluate and measure adsorption relative to total sorption and to measure the heat of adsorption in its dependence on surface coverage, and in order to be able to discuss heterogeneity of... 

Figure 4.14 Nitrogen adsorption isotherm for a SAW device dip coated using a sol containing four oxide precursors ( four component ). This coating was prepared from a solution aged for two weeks at S0°C and pH 3. The large amount of adsorption relative to the film thickness and the Type IV isotherm shapie indicate that this film is highly porous. (Reprinted with permission [lo] by counesy of...

These forces arising in the pores and cracks result, in particular, from repulsion of double electric layers of their walls, as well as from disruption of the water structure. Besides, osmotic pressure may also contribute because the ion concentration inside the pores increases due to adsorption relative to that in the outside solution [3]. 

Coating of the glass surface as well as the diatomaceous earth (Procedure A) produced results for morphine that showed less adsorption relative to a hydrocarbon than when diatomaceous earth only was treated. With the nitrogen-specific detector there was, however, only a slight difference between the methods A and B over a range of about 25-100 ng of morphine. 

Grade Density, Ib-ft Dry Wet pH Water adsorption,% Relative flow rate... 

Sorption equilibria and kinetics are influenced by the nature of the adsorbent and the adsorbate, by the mechanism of adsorption, and by environmental parameters such as temperature, relative humidity, concentration of the adsorbate, and air velocity and turbulence past the adsorbent surface. Air velocity and turbulence only affect sorption kinetics the other parameters also affect equilibria. In general, low adsorbate saturation vapor pressure, low temperature, and high adsorbate concentration in the air increase adsorption. Relative humidity does not always affect adsorption. Colombo et al. (1993) found a 35 % decrease in adsorbed mass when relative humidity was changed from <10 % to 35 %, but only an 8 % decrease when the humidity was increased from 35 % to 70 %. Building materials, which are exposed to indoor air in the normal humidity range of 35-70 %, will typically already be covered by at least one monolayer of adsorbed water, and the formation of multilayers will only have a limited influence on sorption properties for other airborne substances. Kirchner et al. (1997) found that an increase in air velocity increased the rate of desorption of a VOC mixture from painted gypsum, but not from carpet. The air velocity of air above the tuft may be insignificant for the desorption processes of carpet fibers deeper in the tuft. 

Reynders [16, 52] and Joos [ 15, 54]. An example in which the contribution of each component to m is determined by its adsorption relative to the other adsorptions [16, 19] reads... 

All hydrocarbon mixed surfactant systems with dissimilar head groups, such as ionic/nonionic, ionic/ amphoteric, and anionic/cationic, tend to have increased adsorption relative to the pure component adsorption at the same surfactant concentration. This synergisin is analogous to the effect of mixed surfactant systems in forming low CMC surfactant mixtures. It is easier to form a mixed admicelie rather than a pure component admicelie, just as it is easier to form a mixed micelle. 

If the small molecule has a lower refractive index than the carrier solvent and the probe a higher refractive index than the carrier solvent, the calculated level of amount of probe adsorbed will be greater than it really is. If however, both the probe and the small molecule have lower refractive index than the carrier solvent, the amount of probe adsorbed will be smaller than it really is. The extent to which this problem occurs also depends upon the solubility of the small molecule in the carrier solvent. This effect has cansed problems in a recent study [13] of adsorption of various carboxylic acids on to metal hydroxides. Figure 3.4 shows both the heat of adsorption and amount of carboxylic acid adsorbed. It is evident that adsorption of stearic acid (octadecanoic acid) and isostearic acid (16-methyl heptadecanoic acid) from toluene affords apparently reduced levels of adsorption, relative to when adsorbed from heptane. This is due to both the probe and the water having lower refractive indices than toluene. DRIFTS analysis of the respective filler samples retrieved from the FMC cell, however, indicates similar levels of adsorption. Only in the case of adsorption from heptane is the level of adsorption in concordance with theoretical values. This is due to reduced solubility of water in heptane, relative to toluene. 

This is an old fashioned technique, cheap and easy to perform, and not given the attention it warrants in determining levels of geometric coverage. The principle is simple, and adapted from that used to determine surface area [4, 5]. A dye is used which strongly adsorbs on the uncoated filler surface, hut not onto coated areas, and the level of adsorption relative to uncoated filler is then used to assess the amount of untreated surface. 

Let AB be the corresponding differential molar heat of adsorption (and, according to the previous assumptions, this is independent of 0 and also independent of gas pressure, if the gas is perfect). Let /i be the chemical potential of the adsorbed layer and let/e be the chemical potential of the gas at unit pressure. Then the differential Gibbs free energy of adsorption, relative to the gas at unit pressure, is... 

FIGURE 15.6 (a, b) Typical curves for anion and cation equilibrium adsorption in the micropores of activated carbon electrodes, based on data from Ref. 12, expressed as moles of ions adsorbed per volume of micropores. Theoretical lines based on the modified-Donnan model. Note that the micropore charge is always higher than the salt adsorption. ( Salt adsorption relative to the situation of zero charge.)... 

Physisorption is intrinsically weak and is characterized by heats of adsorption relatively small, close to the enthalpy of liquefaction of the adsorptive, typically comprised in the 5-45 kJ mol range it is in general favored by temperatures close... 

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