ELLIPSOMETRIC MEASUREMENT OF UNIVERSAL CRITICAL ADSORPTION INTEGRALS

We present an experimental determination of the universal critical ads orption integrals integral P-+ = integral P-+(x)dx and integral P-- = integral [P--(x)-1]dx, where P-+/-(x) are the one-phase (+) and the tw o-phase (-) universal functions that scale the variation of the local order parameter near a free surface in the vicinity of the Ising criti cal end point. From ellipsometric measurements on three critical binar y liquid mixtures we obtain integral P-+ = 1.86+/-0.11, integral P-- = 1.61+/-0.04, and R(MA) = 1.19+/-0.04 for their ratio, where the quote d uncertainties represent one standard deviation. These values are com pared with recent theoretical and computational results. The renormali zation-group calculation of Diehl and Smock [Phys. Rev. B 47, 5841 (19 93)] obtained integral P-+ = 1.91, integral P-_ = 1.44, and R(MA) = 1. 33, while a Monte Carlo simulation [M. Smock, H. W. Diehl, and D. P. L andau, Per. Bunsenges. Phys. Chem. 98, 486 (1994)] obtained integral P -+ = 2.18, integral P-_ = 1.97, and R(MA) = 1.11. An interpolation to dimension d = 3 of exact calculations for d = 2 and 4 [G. Floter and S . Dietrich, Z. Phys. B 97, 213 (1995)] obtained integral P-+ = 2.27+/- 0.33,integral P-_ = 1.84+/-0.33, and R(MA) = 1.32+/-0.07.