The unwanted adhesion of liquid and solid contaminants to surfaces critically affects the function and performance of materials in a broad range of applications across many industries. Detrimental effects range from vision loss in cameras to increased fuel consumption caused by marine biofouling in maritime industries or severe risks to human health caused by bacterial adhesion in clinical settings. The key difficulty in preventing surface contamination is to overcome the strong tendency of low-surface-tension organic liquids to wet surfaces and the adsorption of organic contaminants (especially proteins, cells or bacteria) to hydrophobic surfaces that compromise the repellent properties.
The Nepenthes pitcher plants can provide inspiration for the design of coatings with efficient repellency towards a wide range of contaminants. In contrast to the lotus effect that inspired the design superhydrophobic surfaces by introducing roughness features to create a solid/air composite surface, the Nepenthes pitcher plants operates on the creation of a fluid/fluid interface between a lubricant firmly locked into a porous surface structure and a non-miscible liquid to be repelled. If properly held in place, the lubricant itself then acts as the repellent surface. The exchange from a solid/liquid to a liquid/liquid interface effectively eliminates pinning points and leads to repellent surfaces with extremely low contact angle hysteresis and sliding angles (i.e. the minimum tilting angle required for a drop to slide off the substrate) – even for liquids with low surface tensions. Additionally, the fluid nature of the interface inherently possesses self-healing characteristics as the lubricant can wick back into damaged parts of the surface.
We present strategies to create lubricant-infused coatings inspired by the pitcher plant and demonstrate applications in self-cleaning coatings on endoscopes and on the prevention of mussel adsorption in marine environments.