Effect of subphase solvent on magnetic nanoparticle monolayer assembled at liquid-air interface.

• FePt-based nanoparticles are self-assembled into superlattices on water subphase. • Magnetic monolayers are formed at liquid-air interface during hexane evaporations. • Miscibility between subphase solvents and hexane affects the ordered monolayer. • High surface tension gradient promotes nanoparticle assembly on the liquid surface. The miscibility and surface tension gradient between the upper and subphase solvents were shown as key factors in the self-assembly of magnetic nanoparticles at the liquid-air interface. The drop-casting of magnetic nanoparticles suspended in hexane does not result in a long-range pattern on the surface of liquid subphases of lower surface tension gradient and higher miscibility with hexane. Instead, nanoparticles disperse into the mixture between upper and subphase solvents. By contrast, the low miscibility and high surface tension gradient between deionized water subphase and hexane lead to a long-range ordered monolayer. Interestingly, domains of hexagonal close-packed superlattices and honeycomb pattern are also obtained. According to this unique finding, a variety of two-dimensional ordered structures can be assembled at water-air interface. [ABSTRACT FROM AUTHOR]