Low Critical Micelle Concentration Discrepancy between Theory and Experiment

Area of Science:

• Physical Chemistry
• Colloid Science
• Surfactant Science

Background:

• Experimental measurements reveal that the critical micelle concentration (CMC) of surfactants plateaus as hydrophobic tail size increases.
• This observation contradicts established theoretical models predicting an exponential decrease in CMC with increasing tail length.

Purpose of the Study:

• To investigate the discrepancy between experimental CMC data and theoretical predictions for surfactants.
• To develop a theoretical framework that explains the observed plateauing of CMC.

Main Methods:

• Utilized a coarse-grained model within the single-chain mean field (SCMF) theory.
• Incorporated micellar kinetic effects and accounted for surfactant adsorption onto experimental surfaces.
• Applied a microscopic model to poly(ethylene oxide) alkyl ether nonionic gemini surfactants.

Main Results:

• The combined SCMF theory with kinetic effects and adsorption corrections successfully reproduced the experimental CMC values.
• Demonstrated that experimental CMCs may not represent true equilibrium values due to extremely long time scales for low CMC systems.

Conclusions:

• The discrepancy between experimental and theoretical CMC values arises from experimental measurements not reaching true equilibrium.
• Kinetic effects and adsorption are crucial factors that must be considered for accurate surfactant behavior modeling.
• The study provides a revised understanding of CMC behavior, particularly for surfactants with low critical micelle concentrations.