Observation of a correlation length finite-size effect in Rayleigh scattering from thin critical fluid films.

Abstract

Rayleigh linewidth data gathered at small scattering angles on critical-mixture films of thickness 2L are found to collapse about a single universal curve, ${\mathrm{\ensuremath{\Gamma}}}^{\mathrm{*}}$(K${\ensuremath{\xi}}^{\mathrm{eff}}$), where ${\mathrm{\ensuremath{\Gamma}}}^{\mathrm{*}}$(x) is the 3D reduced Rayleigh linewidth function, and ${\ensuremath{\xi}}^{\mathrm{eff}}$ is an effective correlation length obeying a general finite-size scaling relation, ${\ensuremath{\xi}}^{\mathrm{eff}/\mathrm{L}=\mathrm{F}(\ensuremath{\xi}/\mathrm{L})}$. The latter reveals that ${\ensuremath{\xi}}^{\mathrm{eff}}$ grows with \ensuremath{\xi} until \ensuremath{\xi}\ensuremath{\approxeq}L, when its growth terminates, implying the existence of surface layers of thickness \ensuremath{\xi} formed by preferential wall-fluid interactions.