Highly ordered micro-sphere films with finely tunable mono- to multi-layer for optical anti-counterfeiting

Highly ordered films of polystyrene (PS) micro-spheres have demonstrated various merits in optoelectronic devices, given their size- and thickness-dependent optical properties. So far, various solution strategies have been developed for making such highly ordered films, which have suffered from the lack of precise control on the film thickness (i.e., layer number of micro-spheres). Here, we developed a facile fibrous liquid bridge strategy for fabricating highly ordered PS micro-sphere films, featured as the finely tunable mono- to multi-layer. Guided by a horizontally placed fiber with both ends passing through a capillary tube, respectively, the solution was transferred steadily onto the target substrate forming a homogeneous liquid film, whose dewetting process thus confines the assembly of micro-spheres in a well-controllable manner. Depending on both the solution-shearing speed and the local concentration, a dynamic equilibrium between liquid transfer and evaporation was realized, which enables the formation of highly ordered micro-sphere films with finely tunable layer numbers. We demonstrated the angle-specific information encryption for anti-counterfeiting by utilizing patterned PS micro-sphere films that modulate structural colors based on layer-dependent optical responses. The result offers a new perspective for fabricating highly ordered film with tunable layers.