Tuneable Topography and Hydrophobicity Mode in Biomimetic Plant-Based Wax Coatings

Across diverse natural surfaces, remarkable interfacial functionalities emerge from micro and nanoscale self-assemblies of wax components. The chemical composition of the epicuticular wax prescribes the intrinsic crystal morphology and resultant topography of the natural surfaces, dictating their interfacial wetting properties. The potential of regulating the topography of identical wax compositions through various crystallization routes is tested here. Crystallization through solvent evaporation produces diverse topographies with enhanced surface hydrophobicity compared to the slow cooling of the wax melt. Further, the microscale interfacial crystalline structure can be deliberately designed to operate in sticky or slippery hydrophobic regimes through control of the supersaturation level during the crystallization process. While the supersaturation level significantly impacts surface wettability by modulating the microscopic aggregation of rice bran wax crystals, the crystal structure at the molecular scale remains effectively unchanged. The relationships between the supersaturation level, surface topography and hydrophobicity modes, primarily derived for rice bran wax, are qualitatively validated for a wider range of plant-based waxes. Crystallization of inherently hydrophobic plant-based waxes from thermodynamically isotropic solutions offers an affordable single-step approach for the fabrication of biodegradable hydrophobic coatings, applicable to versatile materials and geometries. Plant-based waxes, especially those derived from oily seeds, have the potential for the scalable fabrication of bio-degradable coatings. Controlling the kinetics of crystallization allows for modulation of the surface topography and ensuing hydrophobic properties of wax coatings. Using fast-evaporating solvents results in slippery superhydrophobic coatings, while slow-evaporating solvents yield large water contact angles with enhanced adhesion.image