# Rapid Nanocellulose Wet Nanoimprint Lithography for Tunable Structural Color

## TL;DR

This paper introduces a fast method to create structural color in nanocellulose films using wet nanoimprint lithography, much quicker than traditional methods.

## Contribution

The novel contribution is a rapid wet-NIL technique for tunable structural color in nanocellulose films.

## Key findings

- The wet-NIL method is 3–4 orders of magnitude faster than self-assembly for creating structural color.
- Patterned films show durable structural color over humidity cycles and long-term storage.
- The method provides a sustainable and optimized approach for CNC structural color.

## Abstract

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.