A Molecular Dynamics study of structure, stability and fragmentation patterns of Sodium bis(2-ethylhexyl)sulfosuccinate positively charged aggregates in vacuo

Positively charged supramolecular aggregates formed in vacuo by n AOTNa
(sodium bis(2-ethylhexyl)sulfosuccinate) molecules and nc additional sodium ions, i.e.
[AOTnNan+nc
]nc, have been investigated by molecular dynamics (MD) simulations for
n = 1–20 and nc = 0–5. Statistical analysis of physical quantities like gyration radii, atomic
B-factors and moment of inertia tensors provides detailed information on their structural and
dynamical properties. Even for nc = 5, all stable aggregates show a reverse micelle-like structure
with an internal solid-like core including sodium counterions and surfactant polar heads
surrounded by an external layer consisting of the surfactant alkyl chains. Moreover, the aggregate
shapes may be approximated by rather flat and elongated ellipsoids whose longer axis increases
with n and nc. The fragmentation patterns of a number of these aggregates have also been
examined and have been found to markedly depend on the aggregate charge state. In one
particular case, for which experimental findings are available in the literature, a good
agreement is found with the present fragmentation data.