Structure of a fluid interface near the critical point

The structure of the liquid-liquid interface of three very different mixtures (carbon disulfide+methanol, methanol+cyclohexane+deuterated cyclohexane, and $\mathrm{nitrobenzene}+n-\mathrm{d}\mathrm{e}\mathrm{c}\mathrm{a}\mathrm{n}\mathrm{e}$) has been studied using ellipsometry in the reduced temperature range $0.0009<t<\mathrm{}0.042\mathrm{}$. Although the elliptical thickness varies by an order of magnitude between these mixtures, the data from all three mixtures can be scaled to the same universal constant by a combined meanfield plus capillary-wave model of the interface. The universal constant determined experimentally is significantly less than the theoretical value.