Printed Structurally Colored Cellulose Sensors and Displays

Abstract

Hydroxypropyl cellulose (HPC) is a commercially available and biodegradable cellulose derivative, which is known to self-assemble into chiral nematic liquid crystal phases in water. These features, including liquid crystal-induced selective reflections in the visible range, make HPC an ideal biopolymer host material for dynamic structural color-shifting materials. Herein, HPC is used as a starting matrix material and found that, by adding carbon nanotubes (CNT) to an aqueous dispersion of HPC, the color saturation can be improved without influencing the structural color formation and simultaneously conferring electrical conductivity to the material. Additionally, up to 0.4 wt% of cellulose nanofibrils (CNF) can be added to control and tune the rheological properties of the suspension allowing for 3D printability while also maintaining the structural colors. The HPC-CNT-CNF printed composite materials show application for flexible color-changing devices in the form of a dual readout optical and resistive strain sensor and is used as the active material in a dynamic seven-segment color display. This multipurpose color-changing material has the potential to be used in the creation of eco-friendly visual intelligent devices and biodegradable user interfaces and, as such, contributes to the advancement of the field of sustainable and green electronics.