The study of atmospheric aerosols and their role in climate is complicated by the extreme range of length scales on which relevant phenomena occur, extending from the atomic level to the macroscopic.  One important range of length scales that must be bridged to enable descriptions of aerosols is that between the atomic level, where chemical processes take place, and the range over which phase ordering occurs in the organic monolayer found on aerosol surfaces.  Molecular Dynamics simulations representing all atoms in the system explicitly are a powerful tool to compliment experiment and theory in understanding the chemical processes in monolayers, but the range of system sizes that they can explore is limited by the large numbers of interactions that must be computed.  Here we develop coarse-grained descriptions of several lipid and fatty acid molecules representative of those found on aerosol surfaces: Palmitic Acid, DPPA, and Lipid A.  We base our models upon the popular four heavy atom MARTINI coarse-graining paradigm for lipids, which produces stable monolayers with the needed increase in size.  Using these qualitative models as a starting point, we employ minimization of relative entropy to optimize effective interaction potentials with all-atom simulations and study the properties of Langmuir monolayers using these model lipids and their mixtures, including surface-pressure isotherms and phase properties.  We also discuss multi-scale approaches to combine the local information from all atom simulations with the large-scale information from the coarse-grained simulations and build a complete model of aerosol surface layers.

Coarse-grained lipid monolayer simulations for modeling aerosol surfaces

248th National Meeting (2014)

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