Surface amplitude ratios near a critical end point

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, RMA, for the liquid mixtures aniline+cyclohexane and isobutyric acid+water. Our results thus far support the universality hypothesis with RMA=1.3±{}0.1. The universality of RMA 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 RMA to Q is not currently available.