Effect of Surface Curvature on Critical Adsorption

We studied critical adsorption on curved surfaces by utilizing spherical nanoparticles immersed in a critical binary liquid mixture of 2,6 lutidine+water. The temperature dependence of the adsorbed film thickness and excess adsorption was determined from fluorescence correlation spectroscopy measurements of the enlarged effective hydrodynamic radius of the particles. Our results indicated that the adsorbed film thickness is of the order of correlation length associated with concentration fluctuations. The excess adsorption per unit area increases following a power law in reduced temperature with an exponent of -1, which is the mean-field value for the bulk susceptibility exponent. This has been confirmed with silica particles of two different radii, 10 and 25 nm. The results were also compared with the theoretical mean-field scaling function.