Current Research Projects:
Predicting Surface Coverage of Surfactants at the Air/Water Interface using Monte Carlo Simulations and Molecular Thermodynamic Theory
Surfactants are often amphiphilic molecules, molecules containing both a hydrophobic and hydrophilic component, that can self-associate in aqueous media to form complex structures. In aqueous systems, surfactants are thermodynamically driven to reside at interfaces in excess (air/water, water/surfactant, oil/water etc.), thereby lowering the surface tension. In this project, we aim to predict the surface coverage of surfactants at the air/water interface provided a bulk surfactant concentration using Monte Carlo simulations and molecular thermodynamic theory. Specifically, we perform simulations in the Gibbs Ensemble to maintain the thermodynamic equilibrium criteria of equal chemical potentials for surfactants in the bulk and at the air/water interface to accurately obtain relevant thermodynamic properties.
In this ensemble, the bulk and the air-water interface are separate into two boxes, while surfactant molecules are swapped between boxes to maintain a constant chemical potential.
Monte Carlo Package (CASSANDRA) Development
CASSANDRA is an open source atomistic Monte Carlo package developed by the Maginn Group at the University of Notre Dame. In its current state, the package can be used to simulate several thermodynamic ensembles (e.g. NVT, NPT, Gibbs, Grand Canonical) provided a number of Monte Carlo move sets. To date, there are many challenges to efficiently sample equilibrium for complex systems using Monte Carlo simulations. My contribution to the package is to develop advanced Monte Carlo moves that can enhance the sampling of collective dynamics (an important driving force for surfactant self-assembly) and those that can enhance the sampling large molecules to overcome the “insertion” problem.
Moves developed/In development: cluster moves, distance-biased moves, fractional moves, Wang-Landau
Micellaneous: custom potentials, post-analysis toolkit
Past Research Projects:
Elucidating the Molecular Mechanisms of Ionic Liquid Cytotoxicity Using Atomistic and Coarse-Grained Molecular Dynamics Simulations
Interest in ionic liquids (ILs), pure salts that remain liquid near ambient temperatures, has quickly burgeoned within the past decade due to their high tunability, extremely low volatility and solvation prowess, showing promise as new “designer” solvents for a wide range of industrially relevant applications. However, major bottlenecks including their high costs, low biodegradability, and often unknown toxicity have prevented their direct use in the commercial-scale. The major goal of this project is to provide fundamental molecular-level insight in the cytotoxicity mechanisms of ILs. We hopes that such insight can help facilitate the synthesis and design of non-toxic ILs.
Coarse-grained MD simulation of IL-induced morphological disruption to a small vesicle
Insertion of ILs into the vesicle causes the outer leaflet of the vesicle to reassemble and form a micelle.
Atomistic MD simulations of IL insertion into a lipid bilayer
The bilayer thickness undergoes larger fluctuations as the number of inserted ILs increases.
- Yoo, B., Zhu, Y., Maginn, E.J., Molecular mechanism of ionic liquid induced membrane disruption: morphological changes to bilayers, multi-layers and vesicles, Langmuir, (2016).
- Yoo, B.*, Jing, B.*, Jones, S., Lamberti, G., Zhu, Y., Shah, J.K., Maginn, E.J., Molecular mechanism of ionic liquid cytotoxicity probed by an integrated experimental and computational approach, Scientific Reports (2016).
- Yoo, B., Shah, J.K., Zhu, Y., Maginn, E.J., Amphiphilic interactions of imidazolium-based ionic liquids with lipid biomembranes: A molecular simulation study, Soft Matter (2014).
Measurements of Gas and Liquid Solubility in Ionic Liquids
Due to their extremely low volatility, ionic liquids have shown promise as suitable media for many industrial gas-separation processes. In this work, we obtain the relevant thermophysical properties of several popular ILs for such applications.
- Yoo, B., Afzal, W., Prausnitz, J. M., Henry’s constants and activity coefficients of some organic solutes in 1-butyl,3-methylimidazolium hydrogen sulfate and in 1-methyl, 3- trimethylsilyl methylimidazolium chloride, The Journal of Chemical Thermodynamics (2013).
- Yoo, B., Afzal, W., Prausnitz, J.M., Solubility parameters for nine ionic liquids, Industrial & Engineering Chemistry Research (2012).
- Afzal, W., Yoo, B., Prausnitz, J.M., Inert-gas-stripping method for measuring solubilities of sparingly soluble gases in liquids. Solubilities of some gases in protic ionic liquid 1-butyl, 3-hydrogenimidazolium acetate, Industrial & Engineering Chemistry Research (2011)