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

Abstract

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.