  We present simulation results and an explanatory theory on how antagonistic
salts affect the spinodal decomposition of binary fluid mixtures. We find that
spinodal decomposition is arrested and complex structures form only when
electrostatic ion-ion interactions are small. In this case fluid and ion
concentrations couple and the charge field can be approximated as a polynomial
function of the relative fluid concentrations alone. When the solvation energy
associated with transfering an ion from one fluid phase to the other is of the
order of a few k_BT, the coupled fluid and charge fields evolve according to
the Ohta-Kawasaki free energy functional. This allows us to accurately predict
structure sizes and reduce the parameter space to two dimensionless numbers.
The lamellar structures induced by the presence of antagonistic salt in our
simulations exhibit a high degree of nematic ordering and the growth of ordered
domains over time seems to follow a power law. This power law carries a time
exponent proportional to the salt concentration. We reproduce and interpret
neutron scattering data from previous experiments of similar systems. The
dissolution of structures at high salt concentrations observed in these
experiments agrees with our simulations and we explain it as the result of a
vanishing surface tension due to electrostatic contributions. We conclude by
presenting preliminary 3D results showing the same morphologies as predicted by
the Ohta-Kawasaki model as a function of volume fraction and suggesting that
our findings from 2D systems remain valid in 3D.
