Nonmonotonic Scission and Branching Free Energies as Functions of Hydrotrope Concentration for Charged Micelles

Taraknath Mandal, Peter H. Koenig, and Ronald G. Larson
Phys. Rev. Lett. 121, 038001 – Published 16 July 2018
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Abstract

Using coarse-grained molecular dynamics simulations and an umbrella sampling method that uses local surfactant density as a reaction coordinate, we directly calculate, for the first time, both the scission and branching free energies of a model charged micelle [cationic cetyltrimethylammonium chloride (CTAC)] in the presence of inorganic and organic salts (hydrotropes). We find that while inorganic salt only weakly affects the micelle scission energy, organic hydrotropes produce a strong, nonmonotonic dependence of both scission energy and branching on salt concentration. The nonmonotonicity in scission energy is traced to a competition between electrostatic screening of the repulsions among the surfactant head groups and thinning of the micellar core, which result from attachment of the hydrotropes to the micelle surface. We are able to correlate the nonmonotonicity in the scission energy of CTAC micelles with the peak observed experimentally in viscosity versus hydrotrope concentration and the location of this peak in CTAC solutions.

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  • Received 11 November 2017
  • Revised 30 April 2018

DOI:https://doi.org/10.1103/PhysRevLett.121.038001

© 2018 American Physical Society

Physics Subject Headings (PhySH)

Polymers & Soft MatterStatistical Physics & Thermodynamics

Authors & Affiliations

Taraknath Mandal1,*, Peter H. Koenig2, and Ronald G. Larson1,†

  • 1Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA
  • 2Computational Chemistry, Modeling and Simulation, The Procter & Gamble Company, 8611 Beckett Road, West Chester, Ohio 45069, USA

  • *tmandal@umich.edu
  • rlarson@umich.edu

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Issue

Vol. 121, Iss. 3 — 20 July 2018

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