Wettability and Droplet Directional Spread Investigation of Crescent Array Surface Inspired by Slippery Zone of Nepenthes

In this report, the surface topography of crescent array in the Nepenthes slippery zone is measured and bionic fabricated by two-photon polymerization (TPP) technology. A subregion outside-in scanning method (SOSM) is proposed to solve the photoresist converge and large area surface positioning problem existing in bionic crescent array surface (BCAS) fabrication. The geometric parameters of BCAS, including area fraction, height, offset, and outer-inner radius ratio, are systematically investigated to reveal their effects on the hydrophobic performance. Perfluorinated polyether oil and fluorocarbon solvent were used to increase the hydrophobicity and homogeneity of bionic surface. The contact angles of BCASs coated with and without the solution are measured. The maximum contact angle can reach to 152.1 degrees. What's more, considering the anisotropy of BCAS, anisotropic wetting research is conducted. Offset and outer-inner radius ratio are found to have obvious effects on the contact angle differences between convexity and concavity directions. The maximum contact angle difference can reach to 5.1 degrees. Spreading and pinning phenomenon caused by droplet anisotropic wetting are observed and explained. This work is expected to provide references for the BCAS to be applied in super-hydrophobic and droplets motion fields.

Automated summary

This study utilized two-photon polymerization technology to measure the surface topography of crescent arrays in the Nepenthes slippery zone, proposing an outside-in scanning method to address issues in bionic crescent array surface fabrication. It systematically investigated the geometric parameters of BCAS and used perfluorinated polyether oil and fluorocarbon solvent to enhance hydrophobicity. Additionally, anisotropic wetting research was conducted, revealing the effects of offset and outer-inner radius ratio on contact angle differences and observing spreading and pinning phenomena caused by droplet anisotropic wetting.