Preferential adsorption coefficient

Fig. 1.14 Variation of the preferential adsorption coefficient X with the solvent composition for 2,4-DMP,...

The variation of the preferential adsorption coefficient X with the solvent composition for three mixtures is shown in Fig. 1.16. As in the above cases aromatic components are preferentially adsorbed at low compositions, but, p-xylene is more adsorbed than ethylbenzene or toluene. 

According to Grumberg [116], it appears likely that Wvjsc may be a close approximation to the heat of mixing. Table 1.7 shows that the Wvisc values are proportional to the X values. The large negative values of WviSc for p - xylene and mesitylene in a polar solvent can be taken as experimental evidence of an effective enthalpic effect in these binary systems relative to toluene - 2 - propanol system, which influence the value of the preferential adsorption coefficient X. 

Table 1.7 shows the values of the preferential adsorption coefficient X, in mg (mg/g) the molar volumes of the aromatic solvents d - parameters and the values of the interchange energy (Wvisc) of the aromatic solvents - 2 - propanol mixtures. 

Figure 1.17 shows the comparison of theory and experiment for preferential adsorption coefficient X of poly(alkyl methacrylate)s in 1,4-dioxane-methanol. 

A quantitative agreement was found between theory and the experimental results dealing with the dependence of the preferential adsorption coefficient X with the composition, in the cases that were chosen as examples Poly(alkyl methacrylates )/l, 4 - dioxane/methanol [120],... 

The dependence of the preferential adsorption coefficient X, for PDMI, PDEI, PDPI, and PDBI in 1, 4-dioxane (A)/methanol (B) mixtures, as a function of... 

Fig. 1.17 Comparison of theory and experiment for preferential adsorption coefficient, X, of poly(alkyl methacrylate)s in 1,4-dioxane-methanol. (pso = methanol volume fraction). Points Experimental results from ref. [6], (o) PMMA (alkyl = Me) (A) PEMA (Et) ( ) PiBM (iBu). Association equilibria theory. (2-A) Calculated with the parameter values shown in Table I and numbered as 4-6, Curves (a) PMMA (b) PEMA, (c) PiBMA. (2-B) Calculated with the parameter values shown in Table I and numbered as 10-12. Curves (a) PMMA (b) PEMMA (c) PiBMa. (From ref. [120])...

Fig. 1.19 Variation of preferential adsorption coefficient, X, as function of methanol volume fraction tiB0> for PDMI (o), PDEI (A), PDPI ( ), and PDBI ( ), at 298 K. (From ref. [122])...

The case of infinite dilution of the polymer is the one for which total and preferential sorption have been most extensively studied. In this dilute solution limit the interpretation of the preferential adsorption coefficient,, requires knowledge of the g interpretation parameters at infinite dilution, g°, for the polymer in each one of the pure liquids [9],... 

On the other hand, the limiting preferential adsorption coefficient A0 of the second solvent with respect to the solute is defined by... 

The interesting phenomenon where a mixture of two poor solvents or nonsolvents for a polymer provides a medium that acts as a good solvent for die polymers has been the objective of many studies, by light scattering, " viscometry, " sorption equilibrium, and fluorescence. From these techniques, it has been possible to appreciate how the second virial coefficient Aj and the intrinsic viscosity [11] preferential adsorption coefficient A, and excimer and monomer emission ratio Ie/Im are involved by changing solvent composition. They present ([T)], A2) a maximum or a variation at a certain solvent composition where the polymer behaves as through it were dissolved in a good solvent. 

The transition concentrations separating the concentration domain chain flexibility aspects, excluded volume effects and total and preferential adsorption coefficients of the same system have been discussed. 

Table 5.4.4. Parameter values giving the minimum deviation Sj between theory and experiment, for the preferential adsorption coefficient, X, calculated according to the Association Equilibria Theory. Reprinted with permission from Horta et al. °° (Copyright (1989) American Chemical Society)...

It has extended the same theoretical treatment to other closely related systems, a family of poly(dialkyl itaconates). " Preferential adsorption coefficient X was determined and calculated according to the association equilibria theory, and using classical thermodynamic theories. 

The dependence of the preferential adsorption coefficient for poly(dimethyl itaconate) (PDMl), poly(diethyl itaconate) (PDEl), poly(dipropyl itaconate) (PDPl) and poly(dibutyl itaconate) (PDBl), in 1,4-dioxane/methanol mixtures, as a function of the methanol composition (ubo) is shown in Figure 5.4.3. The results are very similar to those of poly(alkyl methacrylates) in the same solvent. " ... 

According to Dondos and Benoit," Read, and Hertz and Strazielle," the dependence of preferential adsorption coefficient X, with molecular weight or with segment density can be expressed empirically as ... 

Polymers dissolved in mixed solvents show the phenomenon of Preferential Adsorption. Experimentally, the preferential adsorption coefficient, X, is determined. A, is the volume of one of the hquids sorbed in excess by the polymer (per unit mass of polymer). In general, the Flory-Huggins model of polymer solutions is used to describe the Preferential Adsorption. More recently, equation of state theories have been applied. " ... 

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