Hierarchical Roughness‐Engineered Superhydrophobic Coatings: A Sustainable Approach Using Eggshell Waste and ZnO Nanoparticles

ABSTRACT Superhydrophobic coatings have attracted significant attention due to their broad functional relevance. However, their fabrication often relies on fluorinated compounds with environmental drawbacks. This study reports the development of sustainable, bioinspired superhydrophobic coatings using materials derived from household waste, including eggshell micro/nanoparticles combined with ZnO nanoparticles. Two coatings with different particle size distributions were applied onto glass and paper substrates, and their surface properties were characterized to determine how particle morphology influences topography and wetting behavior. Light microscopy, CLSM, and scanning electron microscopy–x‐ray energy dispersive spectroscopy (SEM–EDS) confirmed that particle morphology governs surface roughness and the formation of multiscale architectures, which strongly correlated with image‐texture parameters (entropy, fractal dimension, roughness) and high contact angles (> 150°). Dynamic contact‐angle tests revealed distinct wetting regimes: coatings with eggshell microparticles showed higher sliding angles (∼15°), whereas nanoparticle‐based coatings exhibited minimal sliding angles (∼5°). Water‐retention experiments demonstrated that droplets vanished exclusively by evaporation, confirming the coatings’ non‐absorptive nature, while mechanical abrasion and scratching showed that hydrophobicity was largely retained despite surface damage. Overall, this work provides a comprehensive analysis of how particle size, shape, and distribution govern the formation of hierarchical eco‐friendly coatings with stable superhydrophobic behavior, offering a framework for the engineering of future bioinspired water‐repellent surfaces.