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Green solvent exchange enables durable nanocellulose coatings
Researchers have developed a fluorine-free superhydrophobic coating built entirely from cellulose nanofibrils using a sequential solvent exchange strategy. The bio-based system achieves a water contact angle above 155° and withstands abrasion, extreme pH and icing conditions.
The demand for environmentally friendly, high-performance coatings continues to grow across industrial sectors, yet producing robust, fluorine-free superhydrophobic surfaces from purely bio-based feedstocks such as cellulose nanofibrils (CNFs) has remained a significant challenge. A key obstacle is the irreversible aggregation of hydrophilic CNFs during drying, caused by strong inter-fibrillar hydrogen bonding that compromises nanoscale structure and downstream processability.
To address this issue, the research team developed a sequential ethanol/n-butanol solvent exchange process combined with disruption of the electric double layer (EDL) using potassium acetate. This approach introduced steric hindrance between fibrils and suppressed hydrogen bond reconstruction, enabling CNFs to be transferred from an aqueous dispersion into a stable cyclohexane-based dispersion suitable for scalable spray deposition.
Hierarchical roughness and dual silane modification
The nanostructured framework was combined with polydimethylsiloxane (PDMS) as a flexible, hydrophobic binder, followed by vapour-phase modification with methyltrimethoxysilane (MTMS). This dual silane strategy produced a fluorine-free surface with low surface energy and well-defined hierarchical roughness. The resulting coating exhibited a stable Cassie–Baxter wetting state, with a water contact angle of 155.3° ± 1.6° and a sliding angle below 10°.
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Durability under harsh conditions
Beyond its wetting performance, the silanised micro/nano-interface demonstrated notable dynamic stability. The coating retained its superhydrophobic behaviour under rigorous mechanical abrasion, exposure to extreme pH environments between 1 and 12, contact with salt solutions and sub-zero icing conditions. According to the authors, this work provides a viable pathway to overcome the processing bottleneck of hydrophilic biopolymers and supports the development of durable, PFAS-free surface engineering solutions based on renewable raw materials.
Source: Ma, H. et al., Fabrication of nanocellulose-based superhydrophobic coatings via a green solvent exchange strategy. Progress in Organic Coatings, 110307 (2026).
