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

Abstract

Abstract. Here we present experimental surface tension isotherms of mixed solutions of two surfactants, sodium dodecylsulfate (SDS) and cocoamidopropyl betaine (Betaine), measured by means of the Wilhelmy plate method. The kinetics of surface tension relaxation exhibits two characteristic timescales, which have been distinguished to determine correctly the equilibrium surface tension. The transition from the zwitterionic to the cationic form of Betaine is detected by surface tension measurements. The critical micellization concentration (cmc) increases monotonically with the rise of the mole fraction of SDS in the surfactant blend. The experimental surface tension isotherms are fitted by means of the two-component van der Waals model, and an excellent agreement between theory and experiment was achieved. Having determined the parameters of the model, we calculated different properties of the mixed surfactant adsorption layer at various concentrations of SDS, Betaine and salt. Such properties are the adsorptions of the two surfactants; the surface dilatational elasticity, the occupancy of the Stern layer by bound counterions, the surface electric potential, etc. In particular, the addition of a small amount of Betaine to SDS significantly increases the surface elasticity. The results could be further applied to predict the thickness and stability of foam films, or the size of the rodlike micelles in the mixed solutions of SDS and Betaine.

Rheology of wormlike micelles in mixed solutions of cocoamidopropyl betaine and sodium dodecylbenzenesulfonate

“…The electrokinetic curve obtained for the CAPB solution reaches pI at pH close to 3.37. This value is consistent with that determined for the CAPB solutions by Danov et al,[13] based on surface tension measurements(pH = 3.2). Therefore, cationic form of the surfactant is present in a relatively strongly acidic environment (pH < 3.4).…”

“…One of the best known and most commonly used zwitterionic surfactant is cocamidopropyl betaine (CAPB), which properties are dependent on the pH of solution [12,13]. Below the isoelectric point (at acidic pH) betaine is in the cationic form [14,15].…”

Adsorption and structure of the adsorbed layer of ionic surfactants

“…Later, they applied the proposed approach to a comparative study of the van der Waals and Frumkin isotherms [10], and to mixtures of ionic-non-ionic [11,12] and anionic-zwitterionic [13] surfactants.…”

Pozzolanic hardened three-phase-foams

“…The lipophilic part consists of a C 12 -chain from coconut fatty acid, and the hydrophilic content from amino acid glycine and a structural bounded quaternary salt (NaCl). The pK a is at 5.5 [23]. The second amino function can only be functionalized at pH 6 1.…”