Selective surface modification of free-standing polysaccharide nanosheet with micro/nano-particles identified by structural color changes

The chemical and physical modification of a material surface is important for practical applications. In this study, we utilized the bilateral nature of a free-standing polysaccharide nanosheet as a platform for surface modification, selectively modifying the upper and lower surfaces with different sizes of latex beads. By means of a water-soluble sacrificial layer, we adsorbed latex beads with the diameter of 200 nm onto the obverse surface of the polysaccharide nanosheet as well as latex beads with that of 2 μm onto the reverse side. The optical characteristics of the nanosheet were analyzed on the basis of ‘thin film interference theory’ by making stepwise increments in thickness through sequentially overlaying free-standing 30-nm polysaccharide nanosheets onto a SiO2 substrate. The surface of the polysaccharide nanosheet was quite flat and smooth. Having confirmed by optical and scanning electron microscopy that we had achieved selective surface modification of the polysaccharide nanosheet with micro/nano-latex beads, we noted a unique optical property when the nanosheet was adsorbed on the SiO2 substrate. The localization of the beads on the nanosheet surface produced structural colors in the films due to an optical interference. This selective surface modification technique will be utilized to create ‘smart’ nanocomposites possessing different surface functions.