PROBING THE UNIVERSAL CRITICAL-ADSORPTION PROFILE BY NEUTRON REFLECTOMETRY

We present the results of a neutron-reflectivity study of the universa l critical-adsorption profile near the liquid-vapor interface of a bin ary-liquid mixture (methanol + deuterated cyclohexane) near criticalit y. As the critical temperature is approached from the one-phase region , we observed an abrupt decrease in the intensity of the specularly re flected neutron beam near the total-reflection edge. By interpreting t he observation as the expected neutron-reflectivity discontinuity asso ciated with a slowly decaying power-law profile, we evaluated the powe r-law exponent (beta/nu = 0.50 +/- 0.05).