We report a study of the ordering of the surfactant membranes of cetylpyridiniumchloride-hexanol in heavy brine sponge phase solutions in the proximity of a quartz surface by simultaneous neutron reflectometry (NR) and "near surface" small angle neutron scattering (NS-SANS) measurement in a reflection geometry sample cell. The NR results indicate layered surface ordering correlated with the solid-solution interface and decaying exponentially with depth over distances corresponding to a few membrane separations. The absolutely normalized NS-SANS results are consistent with conventional bulk SANS measurements, also indicating that the layered ordering established very near the surface does not constitute a phase of significant volume. We have compared this local surface ordering with the dilution behavior observed for sponge and lamellar phases in the bulk. At low membrane volume fraction the surface layering periodicity corresponds to the bulk sponge correlation peak, but approaches the smaller periodicities measured for lamellar systems at the same membrane volume fraction at higher concentrations.
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