Superhydrophobic Hierarchical Structures from Self-Assembly of Cellulose-Based Nanoparticles

The research of using bio-based nanocellulose to construct novel structures with tailored functions has attracted wide attention over the past few years. Unlike most of the studies starting with hydrophilic nanoscaled cellulose, undecenoate cellulose esters (UCEs) with different degrees of substitution (DSs) are used in this report to construct (super)hydrophobic coatings. UCE1.9 with a DS of 1.9 is composed of spherical nanoparticles (NPs), which have an average size of 112.8 nm. A crystalline cellulose core is present within UCE1.9 according to solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Self-assembly turned UCE1.9 NPs into microparticles (MPs) via a solvent-exchange process. The self-assembled UCE1.9 MPs dispersed in ethanol are well distributed on diverse substrates by spray coating to form superhydrophobic surfaces with micro/nanoscale hierarchical structures, which showed static water contact angles larger than 150° and sliding angles less than 10°. The prepared superhydrophobic surface holds its original superhydrophobicity when exposed to acidic or alkaline conditions and high temperatures. Moreover, UCE3 NPs constructed by UCE3 molecule chains with a DS of 3 tremendously enhanced the mechanical stability after addition into UCE1.9 MPs coatings, which was evaluated through sandpaper rubbing and tape peeling tests. Thus, these novel (super)hydrophobic coatings derived from sustainable cellulose are promising candidates for constructing biodegradable superhydrophobic materials.