Tuning the photonic properties of graphene oxide suspensions with nanostructured additives.

Photonic materials that can selectively reflect light across the visible spectrum are valuable for applications in optical devices, sensors, and decoration. Although two-dimensional (2D) colloids that stack into layers with spacing of hundreds of nanometers are able to selectively diffract light, controlling their separation in solution has proven challenging. In this work, we investigate the role of additives to control the photonic properties of hybrid colloidal suspensions of graphene oxide (GO). We discovered that low concentrations of colloidal additives like cellulose nanocrystals (CNCs) and clay nanoparticles (hectorite) added to GO suspensions lead to dramatic color changes. These hybrid colloidal suspensions demonstrate tunable structural colors and temperature-sensitive properties that likely originate from the entropically driven ejection of guests between the sheets, and from the interactions between colloidal electrical double layers and additional counterions. On the other hand, blending polymeric or molecular additives with GO suspensions either deteriorates or does not impact the photonic properties. These results are helpful to understand the interaction between GO suspensions and additives over different length scales, and open a path to advancing photonic materials based on hybrid colloidal suspensions.