Rewritable hollow sphere photonic crystal based paper with ionic liquid as ink for a durable written information storage system

Photonic crystals can serve as the basis for rewritable paper systems due to their structural color and its responsiveness to external stimuli. The present study reports on a hollow sphere colloidal photonic crystal system encapsulated by a poly(ethylene glycol) diacrylate polymer matrix. By exposing this system to an ionic liquid ink, the polymer will locally swell, red shifting its structural color away from its neutral blue state. The size of the shift is dependent on the type of ionic liquid and the exposure time. This system was shown to attain a maximum shift of 133 nm, which covers the entire RGB spectrum. Both the shift of the structural color as well as the rewritability of the system after water rinsing was confirmed through reflectance measurements. The use of a non-volatile ionic liquid ink ensures the stability of the system over time, allowing for its use as a durable written information storage system.