Critical interface of an ionic Ising mixture

Ellipsometric measurements at the liquid-liquid interface of a critical ionic Ising mixture yield a decrease in the ellipticity $\overline{\rho }$ as the reduced temperature $t$ is decreased (for $t>\mathrm{}0.002\mathrm{}$) in contrast to a $t^{\beta -\nu }$ power-law divergence found for nonionic Ising mixtures. From this surprising result we infer the existence of an anisotropic interface. A model of such an interface is used to calculate theoretical $\overline{\rho }$ data, which capture some of the characteristics of the experimental results.