Self-Assembled Sodium Dodecyl Sulfate Structures on Mineral Surfaces Following Rapid Solvent Removal

Sodium dodecyl sulfate (SDS) is a widely used surfactant with applications ranging from detergents to cell lysis and nanomaterial exfoliation. Additionally, SDS can form self-assembled structures on different substrates under specific conditions. While extensive research has explored SDS self-assembly at the liquid-solid interface, less is known about the structures formed at the solid-air interface following solvent removal. In this study, we investigated SDS self-assembled structures on HOPG (highly oriented pyrolytic graphite), talc, and mica substrates using spin-coating and spread-coating methods. Scanning probe microscopy revealed a range of morphologies, including hemicylindrical micelles, lamellar bilayers, and quasi-1D structures, shaped by the interaction between SDS and the substrate surface. On HOPG, hemicylindrical micelles were observed in dilute solutions, whereas lamellar 2D structures, likely bilayer stacks, formed in both dilute and concentrated samples. On talc, lamellar bilayers demonstrated temporal evolution and thermal stability up to 160 °C. Mica samples exhibited quasi-1D structures, 2D bilayers, and thinner lamellar 2D structures, with evidence suggesting the presence of a methyl-terminated monolayer. Thermal annealing tests indicated that quasi-1D structures lost organization at 60 °C, whereas bilayers remained stable up to 150 °C, at least. The results highlight the complexity of SDS self-assembly at the solid-air interface, emphasizing the critical role of local environmental factors. These findings provide insights into surfactant behavior during solvent removal and establish a foundation for further exploration of self-assembled systems under ambient conditions.