Abstract
Coatings with specific surface wetting properties are of interest for anti-fouling, anti-fogging, anti-icing, self-cleaning, anti-smudge, and oil-water separation applications. Many previous bioinspired surfaces are of limited use due to a lack of mechanical durability. Here, a layer-by-layer technique is utilized to create coatings with four combinations of water and oil repellency and affinity. An adapted layer-by-layer approach is tailored to yield specific surface properties, resulting in a durable, functional coating. This technique provides necessary flexibility to improve substrate adhesion combined with desirable surface chemistry. Polyelectrolyte binder, SiO2 nanoparticles, and silane or fluorosurfactant layers are deposited, combining surface roughness and necessary chemistry to result in four different coatings: superhydrophilic/superoleophilic, superhydrophobic/superoleophilic, superhydrophobic/superoleophobic, and superhydrophilic/superoleophobic. The superoleophobic coatings display hexadecane contact angles >150° with tilt angles <5°, whilst the superhydrophobic coatings display water contact angles >160° with tilt angles <2°. One coating combines both oleophobic and hydrophobic properties, whilst others mix and match oil and water repellency and affinity. Coating durability was examined through the use of micro/macrowear experiments. These coatings display transparency acceptable for some applications. Fabrication via this novel combination of techniques results in durable, functional coatings displaying improved performance compared to existing work where either durability or functionality is compromised.
Highlights
Coatings with specific surface wetting properties are of interest for anti-fouling, anti-fogging, antiicing, self-cleaning, anti-smudge, and oil-water separation applications
This is most evident in the lotus leaf 5; the superhydrophobic properties of the leaf surface, achieved through the presence of hierarchical structure created by rough papillae and superimposed with hydrophobic wax nanotubules, cause water droplets to roll around the surface of the leaf, collecting contaminants as they go keeping the leaf clean[5]
We investigate a fabrication method that can be adapted to produce a coating that displays the four possible combination of water and oil repellence or affinity
Summary
9 min): 0° Hexadecane: superhydrophilic as intended. Dip coated fluoroalkyl end-capped vinyltrimethoxysilane oligomer, CaSi2 particles. When applied to a porous substrate, the coating will allow the passage of oil but block the passage of water, resulting in their separation Their water repellency makes them ideal for self-cleaning[4,16] and anti-icing[17,18,19] applications. Many current examples of “flip-flop” superhydrophilic/superoleophobic surfaces have several drawbacks including poor oleophobicity[36,37,38] or poor penetration by water resulting in a coating that is initially hydrophobic[34,38,39] Such a “flip-flop” of surface properties can be exploited for a variety of applications, such as oil–water separation and anti-fouling.
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