The chemical reactions caused by atmospheric aerosol particles are substantial elements that influence radiative forcing, chemical reaction cycles, and human health. Although the general properties of aerosol particles, along with the chemical reactions of their exterior are understood, the chemical reactions that occur in the interfacial region remain ambiguous. Due to the complexity of the interfacial region, self assembled reverse micelles (RM) are used as proxies to help develop a complete understanding of the photochemical properties of the region. We performed fully atomistic molecular dynamics simulations to explore the impact of trapped ionic species on the size and shape of reverse micelles. Simulations were run at constant temperature and pressure and under different ionic concentrations. We have analyzed RMs constructed from dioctyl sodium sulfosuccinate (AOT) surrounded by isooctane solvent.<br/>Our simulations of larger reverse micelles from w0 = 10,15,20 provide a template for further RM studies. For each RM size, the ions form layers in the interfacial region. K+ ions reside near the surfactant head groups and even replace the Na+ counter-ion of the surfactant while the Cl- anions are localized in the aqueous core. Density calculations indicate that the interfacial region of the reverse micelles are structured as follows: R-SO3- &gt; Na+ ≥ K+ &gt; Cl- (Core). These trends are now investigated for much smaller reverse micelles, with w0 = 2,3,4,7.5. Our simulations indicate that the trend in shape of reverse micelles continues for smaller reverse micelles. Preliminary simulations show that KCl holds the reverse micelle together more and makes it more spherical. Although, after running multiple simulations of different concentrations we discovered that there is a threshold concentration. When there are too many ions in the core they repel each other, which causes the reverse micelle to lose its spherical shape. Knowledge gained from these simulations will be used to fully understand dynamics of species in the interfacial region of atmospheric aerosol particles.

Interfacial ionic partitioning and its impact on small reverse micelles

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.