P(q) for a disk is given by IF(q) ∼= P(q) ∼ ∆b21 q−2 sin(qd/2) (qd/2) 2 , (14) where ∆b1 is the scattering contrast between the air and the film averaged over the mixed water and surfactant, as shown in Figure 6. At the crossover wave number qc (=2π/...