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Understanding the Behavior of Surfactant Molecules Near Metal-Water and Air-Water Interfaces via Molecular Simulations

Singh, Himanshu
http://orcid.org/0000-0002-8437-686X
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1648085005088302

Abstract Details

2022, Doctor of Philosophy (PhD), Ohio University, Chemical Engineering (Engineering and Technology).
In this work, advanced molecular dynamics simulations were employed to study the adsorption of surfactants at metal-water interfaces. A new sampling methodology was developed in molecular simulations that allows efficient sampling of the most thermodynamically stable adsorbed morphology of adsorbed surfactants. The hydration free energies of surfactants and their micelles were also studied. The major findings of this work are: (a) Both unaggregated surfactants and their micelles strongly adsorb on the bare metal-water interfaces; (b) cationic surfactant micelles experience a free energy barrier to adsorption and adsorb by disintegrating on the surface; (c) hydrophobic interactions between the alkyl tails of surfactants promote adsorption, while the accumulation of charged surfactants on the surface inhibits adsorption. As a result, small alkyl tail (C4) quaternary ammonium surfactants adsorb as a sparse layer. Quaternary ammonium surfactants with longer alkyl tails (C12) adsorb as a hemispherical micelle sitting atop a monolayer of adsorbed molecules lying parallel to the surface. Charge neutral surfactants with long alkyl tails, like decanethiol, adsorb in a high-density morphology with molecules standing up on the surface, and a second layer of molecules lying parallel to the surface. (d) Hydration free energy of alkanes is dictated by the entropic loss of water molecules surrounding the alkanes; (e) addition of a hydroxyl group to the terminal position of the hydrophobic tails of the cationic surfactant molecules helps in reducing their micellization tendency and enhancing their aqueous solubility by two orders of magnitude.
Sumit Sharma (Advisor)
Srdjan Nesic (Committee Member)
Horacio Castillo (Committee Member)
Katherine Cimatu (Committee Member)
David Young (Committee Member)
172 p.
Chemical Engineering; Molecular Physics
Molecular simulations; surfactants; micelles; alkanes; free energy; adsorption; hydration; aqueous solubility

Recommended Citations

Citations

  • Singh, H. (2022). Understanding the Behavior of Surfactant Molecules Near Metal-Water and Air-Water Interfaces via Molecular Simulations [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1648085005088302

    APA Style (7th edition)

  • Singh, Himanshu. Understanding the Behavior of Surfactant Molecules Near Metal-Water and Air-Water Interfaces via Molecular Simulations. 2022. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1648085005088302.

    MLA Style (8th edition)

  • Singh, Himanshu. "Understanding the Behavior of Surfactant Molecules Near Metal-Water and Air-Water Interfaces via Molecular Simulations." Doctoral dissertation, Ohio University, 2022. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1648085005088302

    Chicago Manual of Style (17th edition)

ohiou1648085005088302
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© 2022, all rights reserved.
This open access ETD is published by Ohio University and OhioLINK.