A molecular dynamics study of structure, stability and fragmentation patterns of sodium bis(2-ethylhexyl)sulfosuccinate positively charged aggregates in vacuo

Abstract

Positively charged supramolecular aggregates formed in vacuo by nAOTNa (sodium bis(2-ethylhexyl)sulfosuccinate) molecules and n_c additional sodium ions, i.e. [AOT_nNa_n+nc]^n_c, have been investigated by molecular dynamics (MD) simulations for n = 1–20 and n_c = 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 n_c = 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 n_c. 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.