Surface Tension and Surface Potential of Na n-Dodecyl Sulfate at the Air−Solution Interface:  Model and Experiment

Abstract

Surface potential vs concentration isotherms of Na n-dodecyl sulfate (SDDS) adsorbed at the air−solution interface, measured using the vibrating plate method at various concentrations of added salt, exhibit a pronounced minimum. The results of surface tension measurements indicate that the minimum occurs within the concentration range that corresponds to the transition from the Henry regime of adsorption for low surface coverages to the one typical for adsorption of amphiphiles at high surface coverages. We proposed a simple model of adsorption of ionic surfactants at air−fluid interfaces based on the assumption that surfactant headgroups and counterions can adsorb in the Stern layer at the same Helmholtz plane. The electric potential in the electric double layer was calculated according to the Gouy−Chapman model for the diffuse part of the double layer and a modified Stern model for the inner layer with corrections for the discrete charge effects. The total potential drop across the interface was assumed to consist of two contributions: (i) the potential drop in the diffuse and compact double layers, negative for n-alkyl sulfate ions adsorbed at the air−solution interface, and (ii) a positive contribution due to the effective dipole moment of adsorbed surfactant molecules attributed mainly to the terminal CH3 groups. Our model correctly describes the dependence of the surface tension and surface potential of SDDS solution on its concentration and the amount of added salt.

Classification of Flotation Frothers

“…In the case of surfactants, the plot of the surface tension versus concentration is not linear (Figure 4a), although plotting using a logarithmic scale for concentration (Figure 4b) usually provides a linear part, before it levels off for values characteristic for micellar or pure reagent surface tension. 35] In the case of surfactants, the plot of the surface tension versus concentration is not linear (Figure 4a [37]; methyl isobutyl carbinol (MIBC) [38]; dodecyl trimethylammonium bromide (DTAB): [39]; (b) surfactants (semilog scale) (hexyl ammonium chloride: [35]; Na n-dodecyl sulphate: [40]; diethylene oxide n-decyl ether: [41]). …”

“…Table 10 presents the cσ50 values for selected surfactant frothers. (a) surfactants (acetals [37]; methyl isobutyl carbinol (MIBC) [38]; dodecyl trimethylammonium bromide (DTAB): [39]; (b) surfactants (semilog scale) (hexyl ammonium chloride: [35]; Na n-dodecyl sulphate: [40]; diethylene oxide n-decyl ether: [41]). …”

Mixed Solutions of Anionic and Zwitterionic Surfactant (Betaine): Surface-Tension Isotherms, Adsorption, and Relaxation Kinetics

“…The advance in the theory of adsorption from solutions of ionic surfactants, [1][2][3][4][5][6][7][8][9][10] and their blends with nonionic ones, [1][2][3][4][5][6][7] allows a detailed analysis and computer modeling of the interfacial properties. The development of electric double layer and adsorption of counterions have been taken into account.…”

New Adsorption Model —Theory, Phenomena and New Concept—

“…The value of the surface potential has a high possibility of yielding a measure of the special distribution of ionic charges about this air/solution interface 13,14 . Unfortunately, there are few papers on the surface potential of soluble surfactant solutions 5,15 , as far as the authors know.…”