Reverse micelles provide an important model system to investigate aerosols. The size and composition of reverse micelles is expressed as w0 = [H<sub>2</sub>0]/[surfactant]. Particularly, the long-standing question of description of water as two-state model of core vs interface or three-state model of core-intermediate-interface. Recently, some authors have argued for a description involving far more than 3 layers. Here, we present<br/>results of analysis of water dynamics from fully atomistic molecular dynamics simulations. The simulations were carried out with GROMACS and the CHARMM force field. Reverse micelles of various sizes were constructed with AOT surfactant. Water was represented with the TIP3P model. w0 = 5, 7.5, 10, and 15 sized reverse micelles were simulated with the reverse micelles embedded in isooctane matrix. The simulation trajectories ranged from 100 to 150 ns. Residence time and diffusion coefficients in the simulations both behaved increasingly like bulk water as reverse micelle size increases. Rotational anisotropy autocorrelation was modeled using exponential functions in the short time range of 10-20 ps. Longer time data was modeled as a power law fit. Similarly, the diffusion of water in the reverse micelles was also modeled on a power law fit. All of these metrics provided a progression towards bulk water behavior as the reverse micelle size increases. Our results support a 3-layer model of water in a reverse micelle of core - intermediate - interface. These results extend the understanding of water dynamics in reverse micelles and provide new evidence for the 3-layer model, which has been observed in simulations of SPC/E water model in reverse micelles.

Rotational and diffusion investigations of water in a reverse micelle system

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ACS Fall 2022

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