Dendritic nanopattern for Langmuir layer of Gemini/TiO 2 nanoparticles complex at air–water interface

Abstract

Nanocomposite Langmuir film of Gemini surfactant/TiO 2 nanoparticles was prepared on clear hydrosols subphase of TiO 2 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/TiO 2 nanoparticles composite monolayer is still stable even increasing the surface pressure to 40 mN/m on TiO 2 hydrosols. The dissimilar Langmuir behavior of Gemini/TiO 2 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 TiO 2 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 TiO 2 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.