Solvent-induced symmetry breaking and second order phase transitions

The triiodide ion is an example of a system where symmetry-breaking may be induced by a solvent. The Landau free energy is expected to have a similar form to that for the mean field Ising model, but with solvent strength rather than temperature as the control parameter determining whether there is symmetry breaking. In order to examine the possibility of critical phenomena we have studied the properties of the ion in solvents based on a model for water with charges scaled which causes a change from strong symmetry breaking to no symmetry breaking. The behavior of the susceptibility and the Shannon entropy near the critical point show no divergences. We examine the behavior of a simple model and show that divergences would only be expected in the limit of low temperatures, and the essential difference between the solvent-induced symmetry breaking and the mean field Ising model is that in the latter the observed quantity is an average over many spins, while in the former observations are made on individual molecules.