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Surfactant desorption and scission free energies for cylindrical and spherical micelles from umbrella-sampling molecular dynamics simulations.
- Source :
-
Journal of Colloid & Interface Science . Oct2021, Vol. 599, p773-784. 12p. - Publication Year :
- 2021
-
Abstract
- [Display omitted] The free energies associated with adsorption/desorption of individual surfactants from micelles and the fusion/scission of long micelles can be used to estimate the rate constants for micellar kinetics as functions of surfactant and salt concentration. We compute the escape free energies △G esc of surfactant from micelles and the scission free energies △G sciss of long micelles from coarse-grained molecular dynamics simulations coupled with umbrella sampling, for micelles of both sodium dodecylsulfate (SDS) in sodium chloride (NaCl) and cetyltrimethylammonium chloride (CTAC) in sodium salicylate (NaSal). For spherical micelles, △G esc values have maxima at certain aggregation numbers, and at salt-to-surfactant molar concentration ratios R near unity, consistent with experiments. For cylindrical micelles, SDS/NaCl shows a minimum, and CTAC/NaSal a maximum in △G esc , both at R ~ 0.7, while △G sciss of CTAC micelles also peaks at around R ~ 0.7 and that of SDS micelles increases monotonically with R. We explain the non-monotonic dependence of escape and scission free energies on R by a combination of electrostatic screening and the decrease of micelle radius with increasing R. Transitions from predominantly spherical to cylindrical micelles, and between adsorption/desorption and fusion/scission kinetics with changing salt concentration can be inferred from the free energies for CTAC/NaSal. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 00219797
- Volume :
- 599
- Database :
- Academic Search Index
- Journal :
- Journal of Colloid & Interface Science
- Publication Type :
- Academic Journal
- Accession number :
- 150615482
- Full Text :
- https://doi.org/10.1016/j.jcis.2021.04.138