Low Refractive Index Binary Colloidal Crystals from Charged Fluorinated Polymers

Under the right conditions, oppositely charged colloids in water can serve as model ions and form bulk ionic colloidal crystals^[1]. To study structure and crystallization dynamics of these binary systems we developed low refractive index colloidal spheres that can be index matched in water:DMSO mixtures, thus enabling in situ 3D confocal microscopy. Our particles can be made both positively and negatively charged, with uniform sizes ranging from 100 nm and 500 nm. Here, demonstrated that even when dispersed in pure water, our model system crystallizes into nearly transparent ionic colloidal crystals that can be imaged in bulk with single-particle precision.