Contact angle of Nepenthes slippery zone: results from measurement and model analysis

The slippery zone of Nepenthes alata depends on its highly evolved morphology and structure to show remarkable superhydrophobicity, which has gradually become a biomimetic prototype for developing superhydrophobic materials. However, the mechanism governing this phenomenon has not been fully revealed through a model analysis. In this paper, the superhydrophobicity of the slippery zone is studied by contact angle measurement, morphology/structure examination and model analysis. The slippery zone causes an ultrapure water droplet to produce a considerably high contact angle (155.11–158.30°) and has micro–nanoscale hierarchical structures consisting of lunate cells and wax coverings. According to the Cassie–Baxter equation and a self-defined infiltration coefficient, a model was established to analyse the effect of a structure characteristic on the contact angle. The analysis, result showed that the calculated contact angle (154.67–159.49°) was highly consistent with the measured contact angle, indicating that the established model can quantitatively characterise the relationship between the contact angle and the structure characteristic. The authors’ study provides some evidences to further reveal the superhydrophobic mechanism of the slippery zone of N. alata, as well as inspiring the biomimetic development of superhydrophobic surfaces.