Isotherm, adsorption alkyl sulfonate

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. 

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. 

Hoeft [44] also studied the cooperative and competitive adsorption of ionic surfactant mixtures onto hydrophobic surfaces. When shorter alkyl chain surfactants (sodium octyl sulfonate and sodium decyl sulfonate) are adsorbed, the decyl will displace the octyl surfactant. For mixtures of sodium dodecyi sulfonate and sodium octyl sulfonate, however, there appears to be an association between the surfactant molecules leading to enhanced adsorption of the sodium dodecyi sulfonate with no depletion of the octyl sulfonate adsorption. This is shown in Fig, 2, where the lines indicate the expected adsorption determined using a two-component Langmuir adsorption isotherm with the adsorption parameters determined analyzing the data from adsorption of each species individually. Also shown in Fig. 2 is the concentration of surface-active materials in the aqueous phase at equilibrium. In each of these experiments the total molar concentration and amount of surfactant solution added to the latex was a constant, as was the amount of latex. Thus a lower value for the bulk concentration corresponds to greater adsorption. 

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