An examination of the one-parameter adsorption equation without using the Gibbs adsorption equation

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Vol. 512; pp. 137 - 144
• Main Authors: Casandra, Alvin, Tsay, Ruey-Yug, Phan, Chi-M., Lin, Shi-Yow
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.2017
• Subjects: Adsorption isotherm; Equilibrium surface tension; Gibbs adsorption equation; Surfactant; Surfactant; Adsorption isotherm; Gibbs adsorption equation; Equilibrium surface tension
• ISSN: 0927-7757; 1873-4359
• DOI: 10.1016/j.colsurfa.2016.10.030

[Display omitted] •The applicability of the new one-parameter adsorption equation was examined.•This equation was examined with surfactants following Langmuir/Frumkin isotherms.•The effect of Γ∞, a, and K on this adsorption equation was studied theoretically.•This adsorption equation works only for surfactants following K=0.12(Γ∞×1010)−2.6. The study of surfactant adsorption kinetics at a gas-liquid interface has essentially been built with the Gibbs adsorption equation. A simple one-parameter adsorption equation without using the Gibbs adsorption equation was proposed and tested on surfactants C14TAB and C16TAB [Phan et al., Colloids Surfaces A 406 (2012) 24 and Langmuir 29 (2013) 4743] to describe equilibrium surface tension. The applicability of this one-parameter adsorption equation was examined in this study. Theoretical equilibrium surface tension (ST) of nonionic and ionic surfactants generated from the Langmuir and Frumkin isotherms and several sets of experimental ST data were compared with the one-parameter adsorption equation. This study demonstrates that this one-model adsorption equation predicts the equilibrium ST of the aqueous surfactant solutions well following: (i) the nonionic Langmuir isotherm with Γ∞∼20×10−10mol/cm2 or (ii) the nonionic Frumkin isotherm with a specific correlation between maximum surface concentration and intermolecular interaction, K=0.12 (Γ∞×1010)−2.6. It is concluded from this study that the one-parameter adsorption equation is not a general predictive model and cannot describe general equilibrium ST data except under the above conditions.