Surfactant desorption and scission free energies for cylindrical and spherical micelles from umbrella-sampling molecular dynamics simulations.

Autor: Wen B; Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109, United States; State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China., Bai B; State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China., Larson RG; Department of Chemical Engineering, University of Michigan, Ann Arbor, MI 48109, United States. Electronic address: rlarson@umich.edu.
Jazyk: angličtina
Zdroj: Journal of colloid and interface science [J Colloid Interface Sci] 2021 Oct; Vol. 599, pp. 773-784. Date of Electronic Publication: 2021 May 01.
DOI: 10.1016/j.jcis.2021.04.138
Abstrakt: Hypothesis: 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.
Experiments: 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).
Findings: 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.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
(Copyright © 2021 Elsevier Inc. All rights reserved.)
Databáze: MEDLINE
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