PhD project: Michal R. Golos

This project investigates a particularly intriguing and poorly understood mechanism to make plant surfaces slippery for insects: ‘aquaplaning’ on fully wettable, water-lubricated leaf surfaces. Wetness-activated slipperiness is found in two unrelated groups of carnivorous pitcher plants, Nepenthes and Heliamphora. We want to understand how macroscopic and microscopic plant surface features impact (1) wettability and (2) water spreading on plant surfaces, and (3) how these properties affect the ability of insects and contaminants to adhere to the surface.

Nepenthes rafflesiana pitchers growing in a roadside habitat in Brunei Darussalam, Northern Borneo. Different growth stages of pitchers as well as an old inflorescence with open (and empty) seed pods can be seen.

Most but not all plant surfaces are water-repellent. The highly wettable – ‘superhydrophilic’ – trapping surfaces of the pitcher plants that we study are a rare exception to this rule. We want to know what makes these surfaces so extraordinarily wettable, and which features facilitate and direct water spreading on the surface. To answer these questions we take advantage of the natural variation of surface features and wettability found in the species-rich Nepenthes and Heliamphora systems, as well as employing artificial surfaces with precisely defined surface patterns to disentangle the effects of surface topography and chemistry. Together with David Labonte (Imperial College), we investigate how the shape, dimensions, spacing and tilting angle of surface features influence the overall wettability of the surface, and the direction and speed of water spreading across it. To shed light on the contribution of surface chemistry, we collaborate with a world expert on plant waxes, Reinhard Jetter in Vancouver, as well as with local analytical chemist Ian Bull. To this end, we modify the degree of hydrophilicity of artificial surfaces with defined topographical features, and we directly sample and analyse plant surface waxes, using Gas Chromatography – Mass Spectrometry (GC-MS) and state-of-the-art ToF-SIMS analysis. In collaboration with Albert Baars’ group in Bremen, we develop computational fluid dynamics models to simulate water spreading and identify the functional boundaries of surface topography.

By adding a blue dye, we can visualise water spreading on the pitcher rim of Nepenthes x hookeriana in the lab.