Modeling Adsorption of Cationic Surfactants at Air/Water Interface without Using the Gibbs Equation

Abstract

The Gibbs adsorption equation has been indispensable in predicting the surfactant adsorption at the interfaces, with many applications in industrial and natural processes. This study uses a new theoretical framework to model surfactant adsorption at the air/water interface without the Gibbs equation. The model was applied to two surfactants, C14TAB and C16TAB, to determine the maximum surface excesses. The obtained values demonstrated a fundamental change, which was verified by simulations, in the molecular arrangement at the interface. The new insights, in combination with recent discoveries in the field, expose the limitations of applying the Gibbs adsorption equation to cationic surfactants at the air/water interface.

Dynamic adsorption of a gemini surfactant at the air/water interface

“…Consequently, the relationship is applied to the dynamic adsorption at different concentration. For 2-nanonol [19] and alkyl trimethylammonium bromide [18], the relation between interfacial tension and concentration is given by:…”

“…MPT-C (Lauda, Germany) employing maximum bubble pressure method [18] was used to measure dynamic surface tension. All the measurements were conducted at room temperature (25 o C).…”

“…[9]. From the adsorption constants, one can compare the gemini surfactant with cationic surfactants [18]. The saturated surface excess of C12C3C12 is lower than that of both C16TAB and C14TAB ( Figure 5).…”

“…Recently, we developed a new model for dynamic surface tension without using Eq. (1)[18]. The model was successfully applied to two cationic surfactants myristyltrimethylammonium bromide (C14TAB) and cetyltrimethylammonium bromide (C16TAB).…”

Dynamic adsorption of cetyl trimethyl ammonium bromide at decane/water interface

“…The model has been applied successfully on C 14 TAB and C 16 TAB [28] as well as a gemini surfactant [29] at air/water interface. The model is based on the following relationship:…”