Surface amplitude ratios near a critical end point

Abstract

We provide the first experimental test of the universality of a surface amplitude ratio near a critical end point by measuring the modified critical adsorption amplitude ratio, ${\mathit{R}}_{\mathit{M}\mathit{A}}$, for the liquid mixtures aniline+cyclohexane and isobutyric acid+water. Our results thus far support the universality hypothesis with ${\mathit{R}}_{\mathit{M}\mathit{A}}$=1.3±0.1. The universality of ${\mathit{R}}_{\mathit{M}\mathit{A}}$ would imply that the surface tension amplitude ratio Q is universal in agreement with the predictions of Fisher and Upton; however, a precise connection relating ${\mathit{R}}_{\mathit{M}\mathit{A}}$ to Q is not currently available.