Dendritic nanopattern for Langmuir layer of Gemini/TiO2 nanoparticles complex at air–water interface

Nanocomposite Langmuir film of Gemini surfactant/TiO₂ nanoparticles was prepared on clear hydrosols subphase of TiO₂ nanoparticles with average diameters of 8 nm. In comparison with ultrapure water subphase, the surface pressure–area isotherm of Gemini monolayer was significantly expanded in the presence of the titanium oxide nanoparticles. The collapse pressure of Gemini monolayer on pure water is 34 mN/m. While Gemini/TiO₂ nanoparticles composite monolayer is still stable even increasing the surface pressure to 40 mN/m on TiO₂ hydrosols. The dissimilar Langmuir behavior of Gemini/TiO₂ nanoparticles nanocomposite monolayer at air–water interface suggests that interaction between Gemini monolayer and titanium oxide nanoparticles at subphase obviously exists. Morphology of the Langmuir layer investigated via transmission electron microscope indicates that TiO₂ nanoparticles transferred from subphase into Gemini monolayer to form complex. The complex becomes a regular dendritic nanocomposite system gradually as the surface pressure increasing. A mechanism involves the unique molecular structure of Gemini, and the electrostatic interaction between charged TiO₂ nanoparticles and the ionic head groups of Gemini was proposed to explain this phenomenon. The method maybe allows us to introduce some small molecules, instead of conventional dendritic large molecules, to design nanocomposite Langmuir films with desirable nanopattern.