Study of repellence on polymeric surfaces with two individually adjustable pore hierarchies

Highly repellent surfaces offer many interesting applications as oil-repellent textiles and self-cleaning coatings, making these surfaces highly sought-after. Engineering these repellent surfaces requires the combination of a low surface energy material with special surface geometries with multiple levels of hierarchy in roughness. Yet, the current approaches for the fabrication of these surfaces have many drawbacks (complex fabrication techniques, fragile nature of the surface features with low abrasion resistances) that preventing their wider application. Here, we present a study of a new double-hierarchical Fluoropor which allows creating a bulk-porous fluorinated polymer foam with two individually tunable pore hierarchies. We combined our previous structuring approach for the micro/nanoscale (addition of an adaptable porogen mixture to the monomer) with sacrificial templating utilizing spherical polystyrene particles to obtain a second micropore hierarchy, resulting in a novel double hierarchical material. We found that a micro-/nanoporosity with a larger pore structure in combination with a higher volumetric loading of structuring particles was beneficial to increase the repellence. We found the highest repellence for double-hierarchical Fluoropor with a bulk-porosity with 259 nm median pore diameter structured with 50 vol% of 40 mu m sized microspheres. These superhydrophobic surface showed high static contact angles for ethylene glycol of 164 degrees with a roll-off angle of 13 degrees and a static contact angle for n-hexadecane of 145 degrees. The material was covalently coated onto technical substrates (glass, copper, steel) and demonstrated good self-clean abilities for inorganic as well for organic contaminants. Abrasion test with 1000 cycles showed the repellence was not affected and persisted.