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

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