Dynamic Light Scattering in a Sponge Phase of a Nonionic Surfactant

The fluctuation of bilayers in the sponge (L₃) phase of the binary mixture of a nonionic surfactant, pentaethylene glycol dodecyl ether (C₁₂E₅), and water is studied by the dynamic light scattering spectroscopy. In concentrated solution, the autocorrelation function of the scattered light intensity shows almost a single exponential decay and the inverse of correlation time Γ is proportional to the square of scattering wavevector q. In dilute solution, the autocorrelation function shows a stretched exponential decay and the dispersion of Γ shows a crossover behavior from Γ∝q² to Γ∝q³ as q increases. It is found that the dispersions of Γ at various concentrations and temperatures can be scaled into the universal curve. The results for dilute solution are compared with a recent theory concerning to the thermal fluctuation of membranes.