Adsorption plateau

Adhesive force, non-Brownian particles, 549 Admicelle formation, 277 Adsorption flow rate, 514 mechanism, 646-647 on reservoir rocks, 224 patterns, on kaolinite, 231 process, kinetics, 487 reactions, nonporous surfaces, 646 surface area of sand, 251 surfactant on porous media, 510 Adsorption-desorption equilibria, dynamic, 279-239 Adsorption plateau, calcium concentration, 229... 

Figure 9 shows adsorption isotherms for this protein on the various sorbents. As is usually observed for proteins at surfaces, the adsorption affinity is higher for the hydrophobic surfaces than for the hydrophilic ones. The adsorption plateau-values at silica and PS- (EO)8, approximately... 

The saturation adsorption (plateau) was found to be 4.26 mg m-, which is in close agreement with the value obtained before (18) for the same PVA sample on a similar latex. 

The EDS measurements indicated that amounts of Mg, A1 and Na were quite constant in all particles and regions analysed, including the restricted regions over the nanoribbons pattern. The amount of S increased with increasing surfactant concentration in the adsorption process, but remained almost constant in the solids obtained at the adsorption plateau surfactant concentrations. Analysis of the pattern observed over the nanoribbons showed an S amount very similar to that observed in regions outside the nanoribbons. 

In general, the adsorption of ionic surfactants follows the Langmuir isotherm, as discussed in Section 4.1. The adsorption of the surfactants onto the solid surfaces is dependent on the orientation and the packing efficiency of the solid surfaces. The onset of the adsorption plateau may occur at the critical micelle concentration (c.m.c.) of the surfactant in water, as shown in Figure 4.28. If the adsorption isotherm... 

Figure 7 shows adsorption isotherms for this protein on the different sorbents. The adsorption plateau-values at PS-(EO)8, approximately 2.5 mg m 2, is compatible with a complete monolayer of side-on adsorbed a-chymotrypsin molecules. Adsorption saturation at the PS and, even more so, the Teflon surfaces, is beyond monolayer coverage suggesting that on these hydrophobic surfaces the protein molecules are severely perturbed as to accommodate more protein mass in the adsorbed layers and/or adsorption of a second layer of protein molecules (possibly triggered by structurally altered molecules in the... 

Calcium chloride, hydrochloric acid, or ethanol at low concentrations do not modify the adsorption plateau nevertheless, the saturation is attained at a different equilibrium concentration due to the changes in the solubility behavior of the surfactant in the presence of these additives. When the concentration of ethanol is 25% (6 molar), the adsorption maximum is reduced to 0.8 p moles m indicating that for this rather high concentration of ethanol, the surfactant does not completely dislocate the alcohol from the solid surface. 

These limits are somewhat arbitrary pore filling mechanisms also depend on the shapes of the pores and on the size of the adsorptive molecule. Despite this Inherent vagueness, the classification has its use as a first means of discrimination because it points to different pore filling mechanisms macropores are so wide that they behave as "virtually flat" surfaces, mesopores are mainly responsible for capillary condensation, whereas micropores are so narrow that one cannot speak of a macroscopic fluid in them. Because in micropore Jilling adsorbates are only a few layers thick, an adsorption plateau is found suggesting monolayer filling and applicability of the Langmuir or Volmer premises. This mechanism Is distinct from that in meso- and macropores. 

The coefficient 832 is increased by 10 times in Cases Adi to Ad5 based on Cases krl to kr5. The results are shown in Table 8.5. Interestingly, the adsorption in Case Adi is the same as that in Case krl of type in, and the adsorption in Cases Ad2 to Ad4 is even lower than that in Cases kr2 to kr4. The recovery factors of Cases Adi to Ad5 are very close to those of the reference cases krl to kr5, respectively. The comparison of the results of these two groups shows that 832 is not a sensitive parameter because the adsorption plateau is In the data set, b3 = 1000. When 832 is increased by 10 times, the incremental effect to adsorption is only 9/1000. 

Adsorption on Silica Gel. The adsorption isotherms of sodium dodecylbenzene sulfonate and TRS 10-410 on silica gel at 30°C and pH =5.8 are shown in Figure 2 for zero and one wt. % NaCl. Although the equivalent weights of these surfactants differ substantially (SDBS = 348 TRS-10-410=418) the isotherms are very similar in shape there is a concave toe, a shoulder, and a long flat plateau in each case. The addition of one wt.% NaCl to the solution results in a sharp reduction in the adsorption plateau (or saturation level) for SDBS (one wt.% NaCl causes salting-out of TRS-10-410, see Table I, so no adsorption isotherm was measured for TRS-10-410 and one wt % NaCl). 

In interpreting adsorption isotherms, a distinction should be made between very low coverage (initial part of the isotherm), where the protein molecules interact with the sorbent surface only, and high surface coverage (adsorption plateau), where lateral interactions between the adsorbed molecules play a role as well. 

In these dilute solutions, the effect of solvency is most clearly seen, with a poor solvent (x = 0.5) giving the highest adsorbed amounts. In a good solvent (X = 0), 0 is much smaller (see the dashed lines in Figure 16.3) and it levels off for long chains to attain an adsorption plateau which is essentially independent of the molecular weight. It should be noted that in most real situations the x value is somewhere between 0 and 0.5 (probably nearer the latter value). 

Figure 16.6 shows the adsorption isotherms (at 20°C) of two graft copolymers based on a poly(methyl methacrylate-methacrylic acid) backbone and PEO chains, namely Atlox 4913 and Hypermer CG-6(a) (17). The latter has a higher proportion of poly(methacrylic acid) and hence contains a lower PEG chain density than Atlox 4913. Two latex particles with diameters of 427 and 867 nm were used for these measurements. The adsorption isotherms are of a Langmuir type and the plateau value does not seem to depend on the particle size. However, the adsorption plateau value of Hypermer CG-6(a) (1.2mg m ) is lower than that obtained when using Atlox 4913 (1.6mg m ). This is due to the... 

AFM imaging has been used to identify interfacial aggregate structure above the cmc for a variety of ionic, nonionic, and zwitterionic surfactants on both hydrophobic and hydrophilic surfaces. (Structures far below the cmc, corresponding to the low-density adsorption plateau, cannot be imaged readily because the tip-sample force is strongly hydrophobic and attractive in this regime.) The... 

The adsorption of systems containing NaCl alone and NaCl-Na2C03 were markedly different. For NaCl systems (26.2 and 21 g/1 NaCl) the adsorption isotherms are marked by maxima of approximately 55 and 40 g/1, respectively. The maxima for both systems oecurred at an equilibrium sulfonate concentration slightly below 5 g/1. In eontrast the NaCl-Na2C03 adsorption plateaued at approximately 10 mg/1. 

The appearance of an adsorption plateau region at equilibrium concentrations (molalities) approaching the solubility limit indicates that the phenomenon involves only single solute species that are individually dissolved in the solvent. When the adsorption plateau is observed at lower concentrations (molalities), it is usually argued that surface sites of a given type have been saturated by the adsorbing solute species. 

The molecular packing density from Ic/Ipt data at 1 mM TYR concentration (on the adsorption plateau) was 0.22 nmol/cm, and that from... 

The adsorption of perfluorocarbon surfactants C F2 +i COONa and C F2 +i COOH (/ = 6, 7, and 8) on aluminum oxide has been measured in 0.1 M NaCl and in 1,1,2-trichlorotrifluoroethane (TCFE) [46]. In aqueous solution, maximum adsorption decreased with increasing carbon chain length and the pH of the medium. At an initial pH of 4, the maximum adsorption corresponded to bilevel coverage at higher pH values, an adsorption plateau was attained before complete bilayer formation. Contact angles and friction coefficients for adsorbed films were measured as well. In TCFE [47], the adsorption of the peifluoro acids onto aluminum oxide was cooperative, involving attractive lateral interactions between... 

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