Adsorption isotherms sulfonate

Fig. XI-13. Adsorption isotherms for SNBS (sodium p-3-nonylbenzene sulfonate) (pH 4.1) and DPC (dodecyl pyridinium chloride) (pH 8.0) on mtile at approximately the same surface potential and NaCl concentration of O.OlAf showing the four regimes of surfactant adsorption behavior, from Ref. 175. [Reprinted with permission from Luuk K. Koopal, Ellen M. Lee, and Marcel R. Bohmer, J. Colloid Interface Science, 170, 85-97 (1995). Copyright Academic Press.]...

As the solvent concentration increases, the PIC reagents will interact more strongly with the mobile phase and will be less strongly adsorbed on the reverse phase surface. As a consequence, there will be less ion exchange material on the stationary phase surface. This is clearly demonstrated by the adsorption isotherm of octane sulfonate shown in figure 10. 

The SH signal directly scales as the square of the surface concentration of the optically active compounds, as deduced from Eqs. (3), (4), and (9). Hence, the SHG technique can be used as a determination of the surface coverage. Unfortunately, it is very difficult to obtain an absolute calibration of the SH intensity and therefore to determine the absolute number for the surface density of molecules at the interface. This determination also entails the separate measurement of the hyperpolarizability tensor jS,-, another difficult task because of local fields effects as the coverage increases [53]. However, with a proper normalization of the SH intensity with the one obtained at full monolayer coverage, the adsorption isotherm can still be extracted through the square root of the SH intensity. Such a procedure has been followed at the polarized water-DCE interface, for example, see Fig. 3 in the case of 2-( -octadecylamino)-naphthalene-6-sulfonate (ONS) [54]. The surface coverage 6 takes the form ... 

For the pseudo-binary mixture (a = 0.5) of sulfonate and nonylphenol with 30 E.O., figure 2 shows how the concentration of each of their monomer calculated by the RST theory (1), varies as a function of the overall surfactant concentration. It can be expected that the asymptotic regime in which monomer concentrations are stabilized will correspond to a plateau of the adsorption isotherm for the surfactant mixtures considered. 

The adsorption isotherm obtained for dodecylsulfonate (CDS) on alumina is given in Figure 2. This isotherm is similar to that obtained in the past for sulfonate/alumina systems (4). This isotherm behaves in an s-shaped manner (6) revealing its four characteristic regions of adsorption 1) Electrostatic interaction 2) Lateral association (hemimicellization), 3) Electrostatic hindrance and 4) micellization. 

Comparison of these adsorption isotherms with those obtained for the linear alkyl aryl sulfonates (Figure 6) reveals the behavior of the 2 ( ) HDBS to be close to that which would be expected for a 1 (t> HDBS and that of the 8 ( ) HDBS to be equivalent to that of a tridecyl benzene sulfonate. Development of a cguantitative model that can account for the effect of the position of the benzene group on the chain warrants additional data for a variety of surfactants with branched chains. 

The presence of pre-adsorbed polyacrylic acid significantly reduces the adsorption of sodium dodecylsulfonate on hematite from dilute acidic solutions. Nonionic polyacrylamide was found to have a much lesser effect on the adsorption of sulfonate. The isotherm for sulfonate adsorption in absence of polymer on positively charged hematite exhibits the typical three regions characteristic of physical adsorption in aqueous surfactant systems. Adsorption behavior of the sulfonate and polymer is related to electrokinetic potentials in this system. Contact angle measurements on a hematite disk in sulfonate solutions revealed that pre-adsorption of polymer resulted in reduced surface hydrophobicity. 

C- is also reached in the region cTf conc entratioir 5 CMC (Fig. 7,8). No adsorption isotherms were determined for the flotation experiments shown since we gathered from the data published by Scamehorn et al ( 2), who studied the change of the adsorption density as a function of the composition of binary isomer mixtures of Na-alkylbenzene sulfonates on alumina and kaolinite. 

Figure 1. The electrophoretic behavior and isotherm for the adsorption of sodium dodecyl sulfonate from aqueous solution at pH 7.2, 25°C., and 2 X 10 3M ionic strength (NaCl). The 95% confidence limits for the three straight-line regions of the adsorption isotherm are shown...

Figure 3. Adsorption isotherm for p-toluene sulfonate (O) experimental data, (--------------------------------) 3-parameter equation...

An early paper on the use of ATR for the in - situ monitoring of the adsorption of AOT from heptane and water solutions utilized the intensity of the 0=0 band (near 1740 cm1) and the sulfonate band (1045 cm1) for construction of adsorption isotherms. In addition, the utility of detailed examination of the shifts in the sulfonate band frequency for assessing the headgroup environment in adsorbed layers was discussed (115). 

This was shown e.g. by investigating adsorption isotherms of Na dodecylbenzene-4-sulfonate and Na 4-hexadecyloxytolyl-2-sulfonate on various mineral surfaces differing from each other by the kind of PDFs86 . The potential value in relation to the surfactant concentration reached its maximum in the region of micelle formation and confirmed thus the shape of the adsorption isotherm. The presence of adsorption maxima is explained by a decrease in surfactant adsorption resulting from a desorption effect of micelles on the adsorption film, and by setting a three-component equilibrium (adsorption film - micelle - monomer) at concentrations CMC. This happens because of different ratios of the counter ions to the surfactant ions at the micelle and on the adsorption film. 

In contrast to 20H-AQ monolayers, l-amino-2-sulfonic-4-hydroxyanthraquinone (1,2,4-AQASH) adsorbates exhibit significant lateral interactions, thus requiring the use of the Frumkin adsorption isotherm [10]. Figure 4.6 shows that the optimized Frumkin isotherm provides a satisfactory fit to the experimental surface coverages for monolayers assembled from both the reduced and oxidized forms. 

Figure 4. Adsorption isotherms of different gases on polyether-sulfone Victrex polymer at 35°C. (Reproduced with permission from ref. 22. Copyright 1988 Academic Press.)...

Figure 4.67 shows adsorption isotherms of three anionic surfactants on alumina at favorable electrostatic conditions, namely, of p-3-nonyibenzene sulfonate in the presence of 0.01 mol dm " NaCl at pH 4.1 (Ref. 737), of n-decylbenzene sulfonate at 40 C, at pH 4 in absence of supporting electrolyte (Ref. 717), and of dodecyl sulfate at pH 5.3 in the presence of 0.1 mol dm" NaCl (Ref. 718). The solution concentration and adsorption density in Fig. 4.67 were normalized to the transition point IH/IV, which corresponds to CMC and adsorption saturation. In... 

A four-region adsorption isotherm for SDS. Slopes in regions I-IIf and transition points between regions are compared with results taken from literature. Solution concentrations at breakpoints reported in different publications are more consistent than corresponding adsorption densities. Uptake of preadsorbed dodecyisulfonate (10 mol dm ) at pH 3 is not influenced by addition of TX-lOO (up to 10 mol dm For 5x 10 mol dm dodecyisulfonate the uptake at pH 3 is enhanced in the presence of TX-100. The potential becomes less positive when TX-100 is added at constant dodecyl sulfonate concentration at pH < 8. 

According to the Langmuir isotherm equation, the degree of surfactant adsorption increases with concentration. Note that there are some special cases. Figure 7.47 shows the adsorption isotherm of petroleum sulfonate on kaolinite with or without Ca + present there is a maximum adsorption in the plot of... 

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). 

Fig. 4.3. Adsorption isotherms of Mahogany sulfonate AA on two ground Berea sandstone samples and one crushed Berea sandstone sample.

Information on microviscosity is obtained by studying the excimer forming capabilities of suitable fluorescent probes. The excimer, which is a complex of a ground state and excited state monomer, has a characteristic emission frequency. The intramolecular excimer formation for example, of 1,3-dinaphthyl propane (DNP), is a sensitive function of the microviscosity of its neighborhood. This property, expressed as the ratio of the excimer and monomer yield (/e//m) for DNP, has been determined for dodecyl sulfonate solutions and its adsorbed layer for the various regions of the adsorption isotherm (Fig. 4.18) (Somasundaran et al., 1986). Comparing the ratios thus obtained to the /e//m values of DNP in mixtures of ethanol and glycerol of known viscosities, a microviscosity value of 90 to 120 cPs is obtained for the adsorbed layer in contrast to a value of 8 cPs for micelles. The constancy of microviscosity as reported by DNP is indicative of the existence of a condensed surfactant assembly (solloids) that holds the probe. 

Because amino groups act autocatalytically (15-17) in the presence of water, for acid catalysis an excess of HC1 was used to overcompensate the formation of -NH3+C1 . In these cases, the gels were washed with methanol and water until no Cl" could be detected in the filtrate. How far the incorporation of amino groups into silica could affect the adsorption of acid components was of interest. Lactic acid and a sulfonic acid (a commercially available dye named Telon Light Yellow) were chosen as test components (18). In Figure 7 the adsorption isotherm of lactic acid is shown. Unmodified Si02 does not have remarkable adsorption in aqueous solution under these circumstances. The result shows the effect of the amino modification quite clearly, because the lactic acid load of the adsorbent is remarkable, and it is difficult to adsorb small water-soluble molecules in an aqueous environment. 

In the study by Bocharov and Krasovskij [305], the concentration Cm for maximum surfactant adsorption at the water/air interface and the maximum permissible concentration (MPC) of surfactants present in household waters are compared and a large table of data given. For example, for sodium alkyl sulfates, the MPC and Cm values, respectively, are 0.5 and 0.6 0.1 for dodecyl benzene sulfonate 0.5 and 0.4 0.1. For nonionics R(OC2H4)OH, where R=aliphatic radical and n = ethoxy groups number, these values are for R=C]o- Ci3/n=7 0.1 and 0.12 0.3 for R=Cio- Ci8/n=10 0.1 and 0.10 0.02. Thus, adsorption isotherm studies are very promising for the determination of MPC in comparison with the frequently applied foaming method where the MPC is determined at a concentration where dynamic foam bubbles appear in the waste water. 

---