Self-assembly structures of nonionic surfactants at graphite/solution interfaces

The interfacial self-assembly structures of a series of poly(oxyethylene) n-dodecyl ether (C₁₂E_n) nonionic surfactants on graphite has been imaged by atomic force microscopy using only the steric stabilization force as the contrast mechanism. Aggregates are arranged in parallel stripes perpendicular to the underlying graphite symmetry axes for C₁₂E₅-C₁₂E₁₀. These are interpreted as hemicylindrical micelles, consistent with previous studies of ionic surfactants adsorbed on graphite. C₁₂E₂₃ shows a featureless layer and C₁₂E₃ forms an anchored lamellar phase growing normal to the graphite surface. We relate the interfacial structures to those formed in bulk solution and show that the initially adsorbed molecules template the interfacial aggregates, modifying their self-assembly behavior.