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Superamphiphobic surfaces for chemical processing

Final Report Summary - SUPRO (Superamphiphobic surfaces for chemical processing)

Superhydrophobic surfaces have an enormous potential as future self-cleaning or anti-fouling coatings. However, their widespread use has been limited by contamination with oils and dissolved substances and insufficient mechanical stability. Superamphiphobic surfaces prevent contamination. They not only repel water but also non-polar liquids, surfactant and protein solutions. In the project we developed new and improved methods to make more robust superamphiphobic coatings, characterize them, explore new applications and improve our fundamental theoretical understanding of liquid repellency. Thereby, fabrication, characterization, application and theory were intimately connected with each other.
Fabrication. Based on liquid flame spray, we developed a method to make superamphiphobic layers with high liquid repellency which are mechanically much more robust than previous layers. We further developed the first method to coat the inside of capillaries with a super¬hydro¬phobic coating; before only openly exposed surfaces could be coated. The coating at the same time has an antibiofouling effect. Third, we extended the capability of self-cleaning. Rather than only removing dust we can also remove organic contamination. There¬fore we developed a novel way to coat metal oxide photocatalyst with a stable layer of poly¬dimethyl¬siloxane.
Characterization. Using confocal microscopy, we could image the process of wetting and dewetting of super liquid-repellent surfaces with unprecedent spatial resolution. Further-more, we developed a new method to measure the lateral adhesion of a sessile or sliding drop and at the same time determine the advancing and receding contact angles at a defined speed.
Application. Since liquid drops on super liquid-repellent surfaces have an extremely small contact area we use such surfaces to fabricate micro- to millimeter sized particles of defined architecture. Second, we fabricate superamphiphobic membranes for membrane distillation. First tests for water desalination were quite promising. In the framework of the new FET HARMONIC, we now try to improve durability of such membranes.
Theory. Based on video of drops moving on superamphiphobic surfaces, we developed a theory for energy dissipation of sliding drops. In addition, a phenomenological theory for adaptive wetting was proposed. Now we explore its applicability in daily wetting situations. Using this theory, we can predict dynamic contact angles, even at low speed, where none of the known theories is applicable.