Direct-writing of viscoelastic colloidal inks for customizable patterns with structural colors

Abstract

The structural-color patterns are highly valuable for their light-manipulating and stimulus-responsive properties. However, it has been hard to customize their patterning because of multi-step and complex processes. Here, we report direct-writing of photonic inks where polymer viscosity affects the colloidal crystallinity so that we can easily customize the iridescence. The high fraction of colloids is found to result in high crystallinity and printability including speed and resolution. It can print a photonic line at up to 15 mm/s and achieve the highest reflectance of more than 80% in 10 min after heating. It is interesting to find that the colloidal arrangement is decided by shear conditions during printing, and the rheological properties in this system are related to the microstructure for the first time. This strategy is innovative in that patterning can occur rapidly on any substrates with controllable mechanical traits and no waste of colloids even for multicolor patterning.