Light Scattering in Aqueous LiCl Solutions; Evidence for a Low Temperature Immiscibility

Rayleigh and Brillouin light scattering spectra have been obtained in a number of concentrated aqueous LiCl solutions. The scattering from density fluctuations shows the dispersion effects typical of viscoelastic relaxation as the temperature is decreased. In the same temperature region the Rayleigh scattering associated with fluctuations in concentration becomes quite intense. This is interpreted as portending the presence of a miscibility gap in the $\mathrm{LiCl}–{\mathrm{H}}_2\mathrm{O}$ system. The upper consolute temperature associated with this immiscibility is quite near the glass transition region so that no large‐scale phase separation can be seen. In addition it appears there is yet another mechanism producing Rayleigh scattering in the solutions. We have tentatively identified this as arising from fluctuations in the order parameter(s) describing the progress of ionic hydration reaction(s).