Solution, affinity

The stabilizing function of macromolecular surfactants in solid-liquid systems is exercised through protective colloid action. To be effective, they must have a strong solution affinity for hydrophobic and hydrophilic entities. In liquid-liquid systems, surfactants are more accurately called emulsifiers. The same stabilizing function is exercised in gas-liquid disperse systems where the surfactants are called foam stabilizers. 

From Alfrey s (1947) analysis, the region of the negative slope of polyanions before the minimum viscosity function (gellan in Fig. 6 and CMC in Fig. 7) is a region of declining solute-solvent interaction, followed by an increasing solute-solute affinity the latter continues through to a positive slope after the minimum. 

Suen, S.-Y., Caracotsios, M., and Etzel, M. R. (1993). Sorption kinetics and axial diffusion in binary-solute affinity-membrane bioseparations. Chem. Eng. Sci. 48, 1801-1812. 

The plot of 1/k versus the micellar concentration gave straight lines whose slopes and intercepts allow to calculate the and values to be obtained. IC-, values measure the solute affinity for micelles. should be independent of the nature of the stationary... 

Therefore the greater the solute affinity for the stationary phase, the smaller the value. For comparison and k are related as follows ... 

Consider next the content of the first-order contribution to the activity coefficients in (6.33)-(6.35). Note that all of these contain the quantity GAA. Recall that GAA is a measure of the solute-solute affinity. In the limit of DI, the quantity GAA is still finite, but its effect on the activity coefficient vanishes in the limit pA — 0. It is quite clear on qualitative grounds that the standard chemical potential is determined by the solvent—solvent and solvent—solute affinities (this will be shown more explicitly in the next section). Thus, the effect of solute-solute affinity becomes operative only when we increase the solute concentration so that the solute molecules see each other, which is the reason for the appearance of GAA in (6.33)-(6.35). In addition to G(fA, relation (6.34) also includes C,AI1 and relation (6.35) also includes GBB. 

The quantity Gaa (or G ) is often referred to as representing the solute-solute interaction. In this book, we reserve the term interaction for the direct intermodular interaction operating between two particles. For instance, two hard-sphere solutes of diameter a do not interact with each other at a distance R> a, yet the solute-solute affinity conveyed by Gaa may be different from zero. Therefore, care must be exercised in identifying DI solutions as arising from the absence of solute-solute interactions. 

This low additive concentration Casi < sparks off the gel collapse due to the suddently decreasing polymer-solution affinity. The interface between the outer collapsed and the irmer swollen regions (shrinking front) proceeds from the outside towards the inside of the gel within the time Qlayer thickness at small times t t is proportional to The concentration c i increases with the time according to Eq. (6). 

Adsorption is the physico-chemical interaction between solutes and the membrane. The adsorption of organics, or more specifically humic substances, is considered a major fouling mechanism in water treatment. NOM can either adsorb in the structure of the cake and give the cake cohesion, or in the bulk of the membrane. These interactions are strongly influenced by membrane solute affinities and the... 

The above expression holds at any solute concentration. The analysis of osmotic pressure data for solutes therefore provides an indication of solute-solute affinity at the concentration of interest (Karunaweera et al. 2012). One can also show that MM theory is obtained from FST in the limiting case of an infinitely dilute solute, where both approaches then provide a series expansion in concentration (McMillan and Mayer 1945 Kirkwood and Buff 1951). A more detailed discussion is provided in the literature (Cabezas and O Connell 1993). 

Figure 5.3 illustrates the three-phase model with indication of the partition constants K m and K s- The values of K m and K s give information about the solute affinity to micelles and to the stationary phase, respectively. 

The thermodynamics of the chromatographic process is responsible for the solute retention. The retention volume, Vr, is related to the solute affinity constant for the stationary phase, K, by... 

In the early studies, the micellar reduced efficiency was attributed to a diminished rate constant for solute exit from the micellar aggregates [5]. If the solute stays inside the micelles that move with the mobile phase for a long time, it interacts with less stationary phase. It "sees" a shorter column. Assuming the solute entrance in the micelle is diffusion controlled and equivalent for all solutes, the exit rate constant is inversely proportional to the constant. The solutes with the highest affinity for the micellar phase should be the least retained. Actually, they are the most retained solutes which shows that the solute affinity for the micelles (Pwm) are strongly correlated to the affinity for the surfactant covered stationary phase (Pws)- These combined effects with the hydrophobic solutes show that they are the ones with the poorer efficiency [5]. The reduced solute exit rate from the micelle produces a decreased solute diffusion coefficient in the mobile phase, D. ... 

Figure 6.2 illustrates the decrease of the benzene diffusion coefficient in various micellar solutions. Table 6.1 lists the diffusion coefficients of various solutes in different micellar media. Depending on the solute affinity for the micellar phase, the D , diffusion coefficient can be decreased by a factor varying from 2 to 10 (Figure 6.2). Such a decrease may highly increase the B and C terms of the Knox equation as...

Table 6.4 Effect of Alcohols on the Solute Affinity for the Micellar and Stationary Phases...

In 1964, Merries thought of using micelles as the big objects not retained or excluded by a GPC polymer phase. Small molecules are retained by the pore of the stationary phase. They are less retained when solubilized inside an excluded micelle. The idea was to measure solute affinity for micelles through solute retention times. This was the first time a micellar phase was used in chromatography [16]. This part of MLC history was already exposed in Chapter 3. Terabe and Okada developed a slightly different approach to model the small molecule and ion retention in micellar GPC [ 17, 18]. The equation is ... 

In MEKC, the retention factor is not proportional to the retention time. When the solute affinity for the micelle is very high (large K ), the retention factor is very high, the retention time, tR, is not high but close to the micelle retention time, tmc-... 

The nature of the chelating ligate dictates both the stability of the metal complex and the strength of the metal-solute affinity. IDA is tridentate, which loaves multiple coordination sites on the metal to bind to the protein, whereas... 

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