Journal
JOURNAL OF CHEMICAL PHYSICS
Volume 132, Issue 11, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.3358354
Keywords
aggregation; colloids; molecular dynamics method; surfactants
Funding
- Princeton Center for Complex Materials, National Science Foundation MRSEC [DMR-0819860]
- National Defense Science and Engineering
- Princeton Institute for Computational Science and Engineering
- Princeton University Office of Information Technology
- Direct For Mathematical & Physical Scien
- Division Of Materials Research [819860] Funding Source: National Science Foundation
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We use molecular dynamics simulations over microsecond time scales to study the micellization behavior of recently proposed continuum-space, coarse grained surfactant models. In particular, we focus on the MARTINI model by Marrink [J. Phys. Chem. B 111, 7812 (2007)] and a model by Shinoda [Soft Matter 4, 2454 (2008)]. We obtain the critical micelle concentration (cmc) and equilibrium aggregate size distributions at low surfactant loadings. We present evidence justifying modest extrapolations for determining the cmc at low temperatures, where significant sampling difficulties remain. The replica exchange method provides only modest improvements of sampling efficiency for these systems. We find that the two coarse grained models significantly underpredict experimental cmc near room temperature for zwitterionic surfactants, but are closer to measured values for nonionic ones. The aggregation numbers for both zwitterionic and nonionic surfactants are near those observed experimentally, but the temperature dependence of the cmc is incorrect in both cases, because of the use of an unstructured solvent. Possible refinements to the models to bring them into quantitative agreement with experiment are discussed.
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