Large-area flexible 2D-colloidal crystals produced directly using roll-to-roll processing

We describe a direct deposition method for the manufacture of 2D-colloidal crystal films on flexible substrates using a roll-to-roll technique (R2R). Suspensions of silica (SiO2) particles in ethanol with different concentrations and particle sizes (diameters between 150 nm and 520 nm) were prepared and directly deposited onto PET, ITO/PET and stainless steel substrates via wire-bar R2R. We propose an empirical equation that allows one to predict an optimal concentration of the colloidal suspension as a function of the processing parameters necessary to produce a colloidal monolayer. We argue that the development of a R2R coating technique for the fabrication of 2D nanostructures can overcome some technological obstacles that currently hinder the development of printed photonics, nanofabrication and colloidal lithography.