Soluble Surfactants Undergoing Surface Phase Transitions: A Maxwell Construction and the Dynamic Surface Tension

Area of Science:

• Physical Chemistry
• Surface Science
• Colloid Science

Background:

• Soluble surfactants exhibit complex behavior at interfaces.
• Surface phase transitions, from gaseous to liquid expanded states, influence surface properties.
• Understanding dynamic surface tension is crucial for predicting surfactant behavior.

Purpose of the Study:

• To describe the dynamic surface tension of surfactants undergoing surface phase transitions.
• To determine critical bulk and surface concentrations using a Maxwell construction.
• To model mass transfer kinetics and interpret dynamic surface tension data.

Main Methods:

• Application of the Maxwell construction to the surface equation of state.
• Modeling mass transfer controlled by bulk diffusion and/or adsorption-desorption kinetics.
• Fitting equilibrium data using the Frumkin equation for parameters like Gammainfinity, beta/alpha, and K.
• Interpreting dynamic surface tension data with determined constants.

Main Results:

• The Maxwell construction successfully located the critical bulk concentration (C*) and binodal surface concentrations (GammaG, GammaL).
• Equilibrium data for 7-tetradecyn-6,9-diol were fitted, providing key adsorption parameters.
• Dynamic surface tension evolution was consistent with diffusion-controlled adsorption.

Conclusions:

• The study provides a framework for understanding dynamic surface tension during surfactant phase transitions.
• The Maxwell construction is a valuable tool for locating critical transition parameters.
• Diffusion-controlled adsorption is a key mechanism governing surface tension changes in this system.