Comparison of two methods to estimate the standard free energy of adsorption

Abstract

To determine the increment of the standard free energy per methylene group ∆G 0 CH 2 for ionic and nonionic surfactants, two calculation methods are proposed. One procedure is based on the adsorption energy parameter of the respective adsorption isotherm, and the second on the critical micelle concentration. Experimental surface tension isotherms for two homologous series, a nonionic (C n BHB) and an ionic (C n TAB) surfactant, are used to demonstrate how the methods work. As adsorption isotherms, the Frumkin and the reorientation models provide a rather good description for both surfactants. The free energy increments ∆G 0 obtained from the two methods are the same if the reorientation model is used, but the Frumkin model gives different results.

Heterogemini Surfactants Based on Fatty Acid Synthesis and Interfacial Properties

“…This is in good agreement with Eq. [7]. These results suggest that at the beginning the adsorption is a diffusive process and the γ (t) decay is well described by Eq.…”

“…For all solutions the solvent surface tension, γ 0 , is obtained at the intercept, t = 0 with respect to Eq. [7]. For the surfactant with shorter polyoxyethylene chain, NIHG550, the γ (t) decays to a lower value at a specific time than it does for NIHG750.…”

“…[6] and [7], requires the equilibrium surface tension values for the solvent γ 0 and the solution γ eq , as well as the surface excess . It is generally accepted that the initial adsorption is purely diffusion controlled, but there is some controversy about the underlying mechanism closer to equilibrium (22).…”

“…The short-time data linearize in this representation as predicted by Eq. [7] and γ 0 , the solvent surface tension, is obtained as the intercept (i.e., when t → 0). For all solutions the solvent surface tension, γ 0 , is obtained at the intercept, t = 0.…”

“…These results suggest that at the beginning the adsorption is a diffusive process and the γ (t) decay is well described by Eq. [7]. The results obtained by a linear fit over …”