Monolithic nanocellulose films patterned with flower-shaped and other microstructures: A facile route to modulate topographical, wetting and optical properties

Abstract

Surface microstructures are found in nature as a mean to control wettability and adhesion. Efforts to reproduce similar structures in the design of functional materials, however, require the use of tedious procedures, such as micro- and nanolithography. Herein, we introduce a facile and scalable method to create highly ordered surface microstructures or patterns supported on films comprising the same material, cellulose nanofibrils (CNF). This micropatterning is based on fluid flow through solid grids that transfer three-dimensional designs on the surface of the formed films, with precise control on their spatial distribution. The obtained patterned films can be modulated as far as their wettability, optical and haptic features. The viscosity of the CNF suspension and strength properties of the films are shown as variables that define the architecture of the surface patterns. In particular, multi-scale flower-shaped structures generate new properties, going from super-absorbency through capillary action in the unmodified films to superhydrophobic materials after mild hydrophobization treatment. Our results pave the way to scalable and cost-efficient designs based on CNF for water harvesting, microfluidics, anti-reflective surfaces and haptic devices, among others.