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Title: Determination of the critical micelle concentration in simulations of surfactant systems

Alternative methods for determining the critical micelle concentration (cmc) are investigated using canonical and grand canonical Monte Carlo simulations of a lattice surfactant model. A common measure of the cmc is the “free” (unassociated) surfactant concentration in the presence of micellar aggregates. Many prior simulations of micellizing systems have observed a decrease in the free surfactant concentration with overall surfactant loading for both ionic and nonionic surfactants, contrary to theoretical expectations from mass-action models of aggregation. In the present study, we investigate a simple lattice nonionic surfactant model in implicit solvent, for which highly reproducible simulations are possible in both the canonical ( NVT) and grand canonical ( μVT) ensembles. We confirm the previously observed decrease of free surfactant concentration at higher overall loadings and propose an algorithm for the precise calculation of the excluded volume and effective concentration of unassociated surfactant molecules in the accessible volume of the solution. We find that the cmc can be obtained by correcting the free surfactant concentration for volume exclusion effects resulting from the presence of micellar aggregates. We also develop an improved method for determination of the cmc based on the maximum in curvature for the osmotic pressure curve determined from NVTmore » simulations. Excellent agreement in cmc and other micellar properties between NVT and NVT simulations of different system sizes is observed. In conclusion, the methodological developments in this work are broadly applicable to simulations of aggregating systems using any type of surfactant model (atomistic/coarse grained) or solvent description (explicit/implicit).« less
Authors:
 [1] ; ORCiD logo [1]
  1. Princeton Univ., Princeton, NJ (United States)
Publication Date:
Grant/Contract Number:
SC0002128
Type:
Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 144; Journal Issue: 4; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics (AIP)
Research Org:
Princeton Univ., NJ (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1469187
Alternate Identifier(s):
OSTI ID: 1236409

Santos, Andrew P., and Panagiotopoulos, Athanassios Z.. Determination of the critical micelle concentration in simulations of surfactant systems. United States: N. p., Web. doi:10.1063/1.4940687.
Santos, Andrew P., & Panagiotopoulos, Athanassios Z.. Determination of the critical micelle concentration in simulations of surfactant systems. United States. doi:10.1063/1.4940687.
Santos, Andrew P., and Panagiotopoulos, Athanassios Z.. 2016. "Determination of the critical micelle concentration in simulations of surfactant systems". United States. doi:10.1063/1.4940687. https://www.osti.gov/servlets/purl/1469187.
@article{osti_1469187,
title = {Determination of the critical micelle concentration in simulations of surfactant systems},
author = {Santos, Andrew P. and Panagiotopoulos, Athanassios Z.},
abstractNote = {Alternative methods for determining the critical micelle concentration (cmc) are investigated using canonical and grand canonical Monte Carlo simulations of a lattice surfactant model. A common measure of the cmc is the “free” (unassociated) surfactant concentration in the presence of micellar aggregates. Many prior simulations of micellizing systems have observed a decrease in the free surfactant concentration with overall surfactant loading for both ionic and nonionic surfactants, contrary to theoretical expectations from mass-action models of aggregation. In the present study, we investigate a simple lattice nonionic surfactant model in implicit solvent, for which highly reproducible simulations are possible in both the canonical (NVT) and grand canonical (μVT) ensembles. We confirm the previously observed decrease of free surfactant concentration at higher overall loadings and propose an algorithm for the precise calculation of the excluded volume and effective concentration of unassociated surfactant molecules in the accessible volume of the solution. We find that the cmc can be obtained by correcting the free surfactant concentration for volume exclusion effects resulting from the presence of micellar aggregates. We also develop an improved method for determination of the cmc based on the maximum in curvature for the osmotic pressure curve determined from NVT simulations. Excellent agreement in cmc and other micellar properties between NVT and NVT simulations of different system sizes is observed. In conclusion, the methodological developments in this work are broadly applicable to simulations of aggregating systems using any type of surfactant model (atomistic/coarse grained) or solvent description (explicit/implicit).},
doi = {10.1063/1.4940687},
journal = {Journal of Chemical Physics},
number = 4,
volume = 144,
place = {United States},
year = {2016},
month = {1}
}