Adsorption relaxation for nonionic surfactants under mixed barrier-diffusion and micellization-diffusion control

Area of Science:

• Physical Chemistry
• Surface Science
• Colloid Science

Background:

• Surfactant adsorption and surface tension dynamics are crucial in various interfacial phenomena.
• Understanding relaxation processes requires distinguishing between diffusion and adsorption/micellization kinetics.
• Previous models often simplified the interplay between these factors.

Purpose of the Study:

• To theoretically investigate relaxation processes of surfactant adsorption and surface tension.
• To derive general analytical expressions for relaxation under different concentration regimes.
• To analyze the influence of diffusion, adsorption barriers, and micellization on relaxation times.

Main Methods:

• Theoretical analysis of fluid interfaces with small deviations from equilibrium.
• Derivation of analytical expressions for relaxation processes.
• Asymptotic analysis for short- and long-time limits.
• Application to experimental data for Triton X-100.

Main Results:

• Below CMC, adsorption is mixed barrier-diffusion controlled; short-time is barrier-controlled, long-time is diffusion-controlled.
• Above CMC, adsorption is mixed micellization-diffusion controlled.
• Above CMC, short-time relaxation is diffusion-controlled; long-time is influenced by demicellization and diffusion.
• Micellar effects lead to exponential decay, unlike the typical square-root decay.

Conclusions:

• Developed theoretical framework accurately describes surfactant relaxation dynamics.
• Distinguished the roles of diffusion, adsorption barriers, and micellization in different regimes.
• Successfully applied the model to experimental data, determining the demicellization rate constant for Triton X-100.