Nanogravure Printing for PFAS-Free Water-Repellent Textiles with Hierarchical Roughness.

The development of durable efficient water repellent textiles without perfluoroalkyl and polyfluoroalkyl substances (PFAS) is critical for sustainability. However, alternative alkyl-based coating solutions are generally less efficient. Here, we show how the hydrophobicity of a typical biobased fluorine-free coating (Lamoral A5) can be boosted by the multiscale design of the topographic spectrum of polyester fabrics from the submicrometer to the millimeter range. Using nanogravure printing, we fabricated mechanically robust textiles exhibiting nanopillared arrays superimposed on the intrinsic fabric roughness arising from weave pattern and fibers-in-yarn packing, thereby mimicking natural hierarchical superhydrophobic surfaces. We analyze the roughness spectrum of these surfaces by "Wenzel spectroscopy," a new mathematical analysis combining images obtained at different resolutions and sizes allowing us to identify the contribution of different spatial ranges to the total Wenzel roughness of a surface. Thereby, we demonstrate how the submicrometer components of the roughness spectrum are critical for improving the water repellency of smoother fabrics. Although initially smooth fabrics are in the impregnated Wenzel regime, nanostructuring moves these fabrics toward or into the Cassie-Baxter regime in which air pockets are trapped below water droplets; accordingly, the contact angle increases by 5 to 10°, and the pinning parameter decreases until the Cassie-Baxter state is attained. Initially rougher fabrics, which are already in the Cassie-Baxter regime, are less affected. Our approach demonstrates an inherently scalable, environmentally responsible route to advanced functional textiles, combining nanostructuring and sustainable chemistry for outdoor and protective applications.