  The speculated presence of monomolecular lamellae of antagonistic salts in
oil-water mixtures has left several open questions besides their hypothetical
existence, including their microscopic structure and stabilization mechanism.
Here, we simulate the spontaneous formation of supramolecular aggregates of the
antagonistic salt sodium tetraphenylborate (NaBPh$_4$) in water and
3-methylpyridine (3-MP) at the atomistic level. We show that, indeed, the
lamellae are formed by a monomolecular layer of the anion, enveloped by 3-MP
and hydrated sodium counterions. To understand which thermodynamic forces drive
the aggregation, we compare the full-atomistic model with a simplified one for
the salt and show that the strong hydrophobic effect granted by the large
excluded volume of the anion, together with electrostatic repulsion, suffice to
explain the stability of the monomolecular lamellae.
