Surface hydrophobicity of slippery zones in the pitchers of two Nepenthes species and a hybrid.

Lixin Wang,Qiang Zhou

doi:10.1038/srep19907

Lixin Wang, Qiang Zhou

Open Access

https://doi.org/10.1038/srep19907

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Abstract

To investigate the hydrophobicity of slippery zones, static contact angle measurement and microstructure observation of slippery surfaces from two Nepenthes species and a hybrid were conducted. Marginally different static contact angles were observed, as the smallest (133.83°) and greatest (143.63°) values were recorded for the N. alata and N. miranda respectively, and the median value (140.40°) was presented for the N. khasiana. The slippery zones under investigation exhibited rather similar surface morphologies, but different structural dimensions. These findings probably suggest that the geometrical dimensions of surface architecture exert primary effects on differences in the hydrophobicity of the slippery zone. Based on the Wenzel and Cassie-Baxter equations, models were proposed to analyze the manner in which geometrical dimensions affect the hydrophobicity of the slippery surfaces. The results of our analysis demonstrated that the different structural dimensions of lunate cells and wax platelets make the slippery zones present different real area of the rough surface and thereby generate somewhat distinguishable hydrophobicity. The results support a supplementary interpretation of surface hydrophobicity in plant leaves, and provide a theoretical foundation for developing bioinspired materials with hydrophobic properties and self-cleaning abilities.

Highlights

Carnivorous plants of the genus Nepenthes depend on highly evolved organs called pitchers situated at the tips of their conspicuous leaves[1,2] to efficiently capture and digest predominant arthropods[3,4,5]
The static contact angles recorded for the studied Nepenthes species and hybrid under investigation, as well as other Nepenthes species only presented in the supplementary information, approximately ranged from 128° to 156° (Fig. 1 and S1–S3), indicating that the slippery surfaces of these selected Nepenthes pitchers possess hydrophobic property
Our exhibited results concerning the static contact angle quantitatively described the hydrophobicity of the slippery surfaces from two Nepenthes species and a hybrid; we presented the micro-morphology and surface architecture of these slippery zones

Summary

Introduction

Carnivorous plants of the genus Nepenthes depend on highly evolved organs called pitchers situated at the tips of their conspicuous leaves[1,2] to efficiently capture and digest predominant arthropods[3,4,5]. Considering the wide divergence in macro-morphologies and surface architecture that perform various functions, the Nepenthes pitchers have been typically distinguished by several functional parts: a leaf-shaped lid, a collar-formed peristome, a transitional part, a slippery zone and a digestive region[8,9] Optimized, these different parts fulfill the functions of attracting and trapping insects, retaining and digesting prey, and absorbing nutrients[8]. Within most Nepenthes plants, the slippery zone bears numerous downward-oriented lunate cells and a layer of irregular epicuticular wax coverings[12,16,17,18,19] These extraordinary structures present rather unique slippage property to most arthropods, thereby perform the role of trapping and retaining prey[20,21,22]. The principal objective of our investigation involved the static contact angle measurement and the three-dimensional microstructure examination, is to explore the hydrophobicity of the slippery surfaces of three types of Nepenthes pitchers, propose a scientific explanation for the hydrophobic mechanism

Methods

Results

Conclusion