Rapid Nanocellulose Wet Nanoimprint Lithography for Tunable Structural Color

We report a nanopatterning approach for nanocellulose films capable of generating structural color, within time scales of a few minutes, 3-4 orders of magnitude faster than typical cellulose nanocrystal (CNC) self-assembly into chiral nematic structures. We employ a wet-nanoimprint lithography (wet-NIL) approach, in which a prescribed mold is imprinted onto nanocellulose suspensions, supported by a semipermeable membrane that enables water removal during pattern transfer, and thus film formation. We examine the roles of nanocellulose type, concentration, rheology, imprint pressure, and temperature, as well as pattern geometry, seeking to reduce wet-NIL time scales while ensuring replication fidelity. The dynamic response and durability of the patterned CNC films are examined by light scattering and microscopy over multiple humidity cycles, direct contact with water droplets, and long-term storage (up to 12 months). We then model and optimize the diffractive color selection and vibrancy of the patterned CNC films, yielding the largest angular range of single colors and providing a sustainable approach for CNC structure color, which is benchmarked against chiral self-assembly and hybrid patterning methods.