Monte Carlo simulations probing the liquid/vapour interface of water/hexane mixtures: adsorption thermodynamics, hydrophobic effect, and structural analysis

Mona S. Minkara, Tyler Josephson, Connor L. Venteicher, Jingyi L. Chen, Daniel J. Stein, Cor J. Peters, J. Ilja Siepmann

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

Knowledge about the interfacial properties of water/oil mixtures is important for the petrochemical industry and for understanding detergency and hydrophobic effects. Here, we probe the liquid/vapour interface of water/n-hexane mixtures using configurational-bias Monte Carlo simulations in the (Formula presented.) osmotic Gibbs ensemble. We study the effect of n-hexane at several partial pressures ranging from 25% to 95% of its saturated vapour pressure and observe that the surface tension decreases with increasing n-hexane pressure. Additionally, we analyse the simulation trajectories to provide molecular-level insights on the spatial distribution of n-hexane and the structure of the interface. The n-hexane molecules strongly adsorb from the vapour phase onto the liquid interface with a preferentially parallel orientation with respect to the interface. The surface excess, from the Gibbs adsorption isotherm equation, is calculated and used to systematically define the domain of adsorbed n-hexane. Integrating over this gives the free energy of adsorption of n-hexane, which is highly favourable, varying from (Formula presented.) to (Formula presented.) kJ/mol as the partial pressure of n-hexane is increased. The enrichment of n-hexane molecules on the interface yields a positive deviation from Henry's law at higher partial pressures, providing evidence for favourable adsorbate-adsorbate interactions.

Original languageEnglish (US)
Pages (from-to)3283-3291
Number of pages9
JournalMolecular Physics
Volume116
Issue number21-22
DOIs
StatePublished - Nov 17 2018

Bibliographical note

Funding Information:
This collaborative research was supported by the Abu Dhabi Petroleum Institute Research Center (Project Code LTR14009) and the University of Minnesota Disability Resource Center through access assistants to Dr Minkara; specifically, Tanner Lambson, Tyler Westland, and John Hamill. A portion of the computer resources were provided by the Minnesota Supercomputing Institute at the University of Minnesota.

Funding Information:
This collaborative research was supported by the Abu Dhabi Petroleum Institute Research Center (Project Code LTR14009) and the University of Minnesota Disability Resource Center through access assistants to Dr Minkara; specifically, Tanner Lambson, Tyler Westland, and John Hamill. A portion of the computer resources were provided by the Minnesota Supercomputing Institute at the University of Minnesota. We thank David Harwood for helpful comments.

Keywords

  • Interface
  • adsorption
  • hydrophobic effect
  • osmotic Gibbs ensemble
  • surface tension

Fingerprint Dive into the research topics of 'Monte Carlo simulations probing the liquid/vapour interface of water/hexane mixtures: adsorption thermodynamics, hydrophobic effect, and structural analysis'. Together they form a unique fingerprint.

Cite this