Innovative Solid Slippery Coating: Uniting Mechanical Durability, Optical Transparency, Anti-Icing, and Anti-Graffiti Traits

Abstract

Slippery coatings, such as the slippery liquid-infused porous surface (SLIPS), have gained significant attention for their potential applications in anti-icing and anti-fouling. However, they lack durability when subjected to mechanical impact. In this study, we have developed a robust slippery coating by blending polyurethane acrylate (PUA) with methyltriethoxysilane (MTES) and perfluoropolyether (PFPE) in the solvent of butyl acetate. The resulting mixture is homogeneous and allows for uniform coating on various substrates using a drop coating process followed by drying at 160 °C for 3 h. The cured coating exhibits excellent water repellency (contact angle of ~108° and sliding angle of ~8°), high transparency (average visible transmittance of ~90%), exceptional adherence to the substrate (5B rating according to ASTMD 3359), and remarkable hardness (4H on the pencil hardness scale). Moreover, the coating is quite flexible and can be folded without affecting its wettability. The robustness of the coating is evident in its ability to maintain a sliding angle below 25° even when subjected to abrasion, water jetting, high temperature, and UV irradiation. Due to its excellent nonwetting properties, the coating can be employed in anti-icing, anti-graffiti, and anti-sticking applications. It effectively reduces ice adhesion on aluminum substrates from approximately 217 kPa to 12 kPa. Even after 20 cycles of icing and de-icing, there is only a slight increase in ice adhesion, stabilizing at 40 kPa. The coating can resist graffiti for up to 400 cycles of writing with an oily marker pen and erasing with a tissue. Additionally, the coating allows for easy removal of 3M tape thereon without leaving any residue.

Keywords: anti-freezing; anti-graffiti; anti-smudge; durability; solid slippery coating.

Figure 1

Curing mechanism of the solid slippery coating.

Figure 2

(a) Fourier transform infrared spectrum of the slippery coating. (b) Optical transmittance spectra of the slippery coating on glass measured in the wavelength range from 300 nm to 800 nm. Inset images show a comparison between the bare glass and the glass coated with the slippery coating. (c) Surface morphology of the slippery coating on glass observed using an atomic force microscope. (d) Thickness of the slippery coating observed through cross-section analysis using a scanning electron microscope.

Figure 3

Variation in surface wettability of the slippery coating against the weight of (a) MTES and (b) PFPE in the precursor solution. (c) Snapshot of a water droplet on the slippery coating with the contact angle of 108°. (d) Variation in the sliding velocities of water droplets with different volumes on the inclined coating at different tilt angles. The results in (c,d) are for the coating with the optimized formulation of MTES (1.5 g) and PFPE (0.18 g).

Figure 4

Variation in contact angle (a) and sliding angle (b) over different numbers of abrasion cycles and under different loads for the coating on the glass substrate. SEM images for the coating after abrasion for 500 cycles under a load of 1.25 kPa (c-1,c-2) or 5 kPa (d-1,d-2).

Figure 5

(a) Key parameters for the water jetting test. (b) Variation in the contact angle and the sliding angle against the water jetting time. (c) Macro surface appearance of the slippery coating on the glass after the cross-cutting and tape peeling test.

Figure 6

Snaps of the coated PET film being folded into a "U" shape (a-2) and moved back (a-1) and forth (a-3). (b) Snaps of the coated Al plate folded at a 90° angle (b-1) and then restored to its original state (b-2). A water droplet with the volume of 20 µL is sliding on the crease with the tilting angle of 20° (b-3). Variation in sliding angle and sliding velocity of the coated PET (c) and Al plate (d) with different folding times. A 20 µL water droplet was tested on the coated substrate and the tilting angle was 20°.

Figure 7

Variation in the contact angle and sliding angle against the heating temperature (a) (the heating duration is 1 h) and the UV radiation time (b) for the composite slippery coating. (c) Variation in contact angle against the simulated rain cycles for the composite slippery coating.

Figure 8

(a) Adhesion strength of ice on the bare glass and the slippery coating. (b) Variation in the adhesion strength of ice on the slippery coating against the icing/de-icing cycles.

Figure 9

Comparison of anti-graffiti performance between bare glass (a-1) and the slippery coating after 400 wiping cycles (a-2). Evaluation of anti-sticking performance on bare glass (b-1) and the slippery coating (b-2).