Explicit- and implicit-solvent simulations of micellization in surfactant solutions

Area of Science:

• Computational chemistry and materials science
• Physical chemistry of surfactants and colloids

Background:

• Accurate determination of critical micelle concentration (cmc) is crucial for understanding surfactant behavior in dilute solutions.
• Current simulation methods face challenges with time scales for micelle reorganization and simulating highly dilute systems.

Purpose of the Study:

• To investigate simulation methodologies for obtaining the cmc and aggregate size distribution in dilute surfactant solutions.
• To address limitations in current simulation approaches for predicting surfactant aggregation behavior.

Main Methods:

• Analysis of molecular dynamics (MD) time scales for atomistic surfactant models in explicit solvent.
• Development of a theoretical framework for extrapolating free surfactant concentration to the cmc.
• Exploration of implicit-solvent grand canonical Monte Carlo (GCMC) simulations for systems with hysteresis.

Main Results:

• Atomistic force fields systematically underpredict experimental cmc values, indicating a need for improved models.
• Demonstrated a strong dependence of free surfactant concentration on overall concentration for ionic surfactants.
• Implicit-solvent GCMC simulations offer a viable alternative for strongly micellizing systems exhibiting hysteresis.

Conclusions:

• Current simulation techniques have limitations in accurately predicting cmc and aggregate distributions for practical surfactant systems.
• Improved force fields and advanced simulation techniques like implicit-solvent GCMC are necessary for reliable quantitative predictions.
• The proposed theoretical framework and simulation approaches can aid in interpreting experimental scattering data.