Highly Transparent Anti-Smudge Coatings for Self-Cleaning, Controllable Liquid Transport, and Corrosion Resistance

Abstract

Highly transparent anti-smudge coatings are attractive for diverse fields due to their inherent repellency against various contaminants and the ability to keep surfaces clean. In this work, a novel fluorine-free anti-smudge coating system was developed by using poly(dimethysiloxane), tris(hydroxymethyl) aminomethane, and isophorone diisocynate to synthesize a hexa-functional coating precursor and utilizing hexamethylene diisocyanate trimer as a curing agent. The resultant anti-smudge coatings are highly transparent and can be applied to various substrates. These coatings exhibit repellency against water, hexadecane, ink, pump oil, and crude oil and show self-cleaning performance in air and oily environments. Moreover, they display anti-ink ability and can be employed to reduce bacterial contamination. Of note, they can endow substrates with protection against corrosion from strong acids, strong bases, salt solutions, and even aqua regia. The developed coatings also show potential for controllable liquid transport. Moreover, these versatile coatings are mechanically robust, demonstrating tolerance against abrasion, impact, and bending and also exhibiting excellent adhesion to various substrates, indicative of their availability for widespread applications.

Keywords: anti-ink ability; anti-smudge coatings; corrosion resistance; mechanical robustness; self-cleaning performance.

Figure 1

(a) Chemical structures of precursor agents (PDMS, IPDI, and THAM). (b) Chemical structures of curing agent (HDIT). (c) FTIR spectrum of the cured coatings. (d) Variations of the optical transmittance and the contact angle toward water and hexadecane on the coating surface as a function of coating thickness.

Figure 2

(a) Blue-dyed water droplet and (b) red-dyed hexadecane droplet sliding off the coated glass plate, respectively. Dirt scattered on the coated glass plate and cleaned with (c) water and (d) hexadecane, respectively.

Figure 3

(a) Water droplet sitting in oil (hexadecane) and readily gliding away as the coated glass plate was slightly tilted. The inset indicated that the water droplet had a contact angle of 160.27° in oil. (b) Water droplets spreading on the uncoated glass plate (with a contact angle of 59.23°, as demonstrated in the inset) and pinning tightly. (c) Two water droplets merged into a bigger droplet on the coated glass plate in oil. (d) Controllable cleaning with water droplets by a needle. (e) Dirt being carried away by dropping water droplets in oil.

Figure 4

(a) Water-soluble black ink, (b) pump oil, and (c) crude oil, respectively, on the uncoated glass tube and the final status after application on the coated one. Photographs on the right side were used to compare the repellency of the coatings against the above contaminants. (d) Marker ink (oil-based) traces are left on the uncoated side of a half-coated wristwatch, while ink contracted on the coated side and can easily be removed by wiping with a tissue. (e) Bacterial colonies corresponding to uncoated blank control. (f) Bacterial colonies corresponding to the anti-smudge coatings.

Figure 5

Controllable liquid transport on the coating surface. (a) Schematic illustration of the approach to constructing sliding paths for controllable liquid transport on the coating surface. For interpretation, visually, the yellow represents uncoated regions and substrate, while the blue represents the coated regions, and the red is on behalf of the liquid droplet applied. (b) A hexadecane droplet slides along a curved pattern. (c) A hexadecane droplet directionally glides to the target droplet on the lower left or right. (d) Two droplets sliding along different patterns to merge. The tilting angle was about 17.0°. The path distance for liquid sliding was about 4 mm.

Figure 6

Corrosion resistance tests. (a₁,a₂) Photographs of an aluminum plate with a coated star-shaped pattern before and after being treated with 1.0 M NaOH solution. (b₁,b₂) Images of a steel plate with a coated maple leaf pattern before and after being treated with 1.0 M H₂SO₄ solution. (c₁–c₄) Snapshots of a steel plate with a coated half-moon pattern treated with aqua regia. (d₁,d₂) Comparison of a steel plate with a coated tree pattern before and after treated with 0.5 M CuSO₄ solution. (e) A steel plate bearing coated (middle) and uncoated sections after immersion in a 3.5 wt% NaCl solution for 168 h.

Figure 7

Mechanical robustness of these anti-smudge coatings. (a) Variations in the contact angles and sliding angles toward water and hexadecane as a function of abrasion cycles. (b) Three-dimensional topography image of the coating surface after suffering from 4000 abrasion cycles, and the resultant RMS roughness was 6.41 nm. (c) XPS analysis of the coating surface before and after 4000 abrasion cycles. (d) Sliding of a hexadecane droplet on the coating surface subjected to 4000 abrasion cycles. (e) Adhesion test on a coated tin plate. (f) Impact test (front side) on a coated tin plate.