Double cross-linked transparent superhydrophilic coating capable of anti-fogging even after abrasion and boiling

Abstract

The commercial application of surfaces with superhydrophilic (SHPL) properties is well known as an efficient strategy to address problems such as anti-fogging, anti-frosting, and anti-biological contamination. However, current SHPL coatings are limited by their poor water and abrasion resistances. Thus, herein, to solve these problems active glass was employed as a substrate, and a stable and transparent SHPL solution was prepared via the spraying process. Aqueous polyacrylic resin (PAA), SiO₂ nanoparticles (NPs), tetraethyl orthosilicate (TEOS), and sodium allyl sulfonate (SDS) were utilized as the four main components of the PAA-TEOS-SiO₂ coating. The durability properties including anti-abrasion, resistance to water, and contact component loss were investigated via the Taber abrasion test, boiling water immersion test, and anti-fogging test, respectively. Furthermore, the structure, composition, and wettability of the coating before and after the friction and water immersion tests were compared via water contact angle (WCA) measurements. Furthermore, the effect of the type of resin on the properties of the coating was investigated. The surface morphology of the blended water-based polyacrylic acid (PAA) resin was uniform and flat and its adhesion to the substrate was the highest (4.21 MPa). Considering the durability and optical properties of the coating, the optimal blend was 3 wt% PAA resin, which exhibited a transmittance of 90%. When the content of TEOS, which enhanced the crosslinking in the coating, was increased to 2 wt%, the results showed that the SHPL coating maintained good anti-friction, boiling resistance, and anti-fogging properties under the conditions of 300 cycle Taber friction with 250 g load and soaking in hot water at 100 °C for 1 h. In particular, the excellent durability of strong acid and alkali resistance, heat resistance, and long-term aging resistance will facilitate the commercial viability and expand the application of SHPL coating in various research fields.

Fig. 1. Schematic of detailed manufacturing process.

Fig. 2. (a) Schematic diagram of the double cross-linking design of the anti-fogging SHPL coating. (b) Wettability and (c) anti-fogging performance of the glass substrate and SHPL SiO₂ coating. SEM surface images of (d) SiO₂, (e) PU-SiO₂, and (f) PAA-SiO₂ coating. (g) Transparence, (h) WCA, and (i) adhesion on glass of SiO₂, PU-SiO₂, and PAA-SiO₂ coating. (j) WCA of PU-SiO₂ and PAA-SiO₂ coating after different Taber abrasion cycles.

Fig. 3. (a) Average size and transparency of the PAA-SiO₂ SHPL coating at different mass ratios of PAA. (b) Anti-abrasion cycles and anti-boiling time of PAA-SiO₂ coatings at different mass ratios of PAA. SEM surface image of PAA-SiO₂ coating at (c) 3 wt% and (d) 4 wt% PAA mass ratio.

Fig. 4. Surface SEM images of the PAA-SiO₂ coatings after the Taber abrasion test for (a) 240 r cycles and (b) 300 r cycles. Surface SEM images of the PAA-SiO₂ coatings after boiling immersion test for (c) 40 min and (d) 50 min. Change in (e) sulfur content and (f) wettability of surfactant during Taber abrasion test. Change in (g) sulfur content and (h) wettability of surfactant during boiling immersion test.

Fig. 5. Surface SEM images of the PAA-TEOS-SiO₂ coating with different mass ratios of TEOS: (a) 0.5 wt%, (b) 1 wt%, (c) 1.5 wt%, and (d) 2 wt%. (e) Transparency of the PAA-TEOS-SiO₂ coating with different TEOS contents. (f) Wettability changes after anti-boiling and anti-abrasion tests and (g) anti-fogging performance of the PAA-TEOS-SiO₂ coating with different TEOS contents.

Fig. 6. Surface SEM images of the PAA-TEOS-SiO₂ coating after the Taber abrasion test for 300 r cycles with different mass ratios of TEOS: (a₁) 0.5 wt%, (a₂) 1 wt%, (a₃) 1.5 wt%, and (a₄) 2 wt%. Surface SEM images of the PAA-TEOS-SiO₂ coating after boiling immersion test for 60 min with different mass ratios of TEOS: (b₁) 0.5 wt%, (b₂) 1 wt%, (b₃) 1.5 wt%, and (b₄) 2 wt%. Change in (c) wettability and (d) sulfur content of the surfactant during the Taber abrasion test. Change in (e) wettability and (f) sulfur content of surfactant during boiling immersion test.

Fig. 7. (a) Schematic diagram of the double cross-linking mechanism of the PAA-TEOS-SiO₂ coating. (b) WCA of the SHPL coating after immersion in 1 M acid solution and 1 M alkali solution for different times. (c) Optical pictures of SHPL coating after immersion in 1 M acid solution and 1 M alkali solution for 36 h and 72 h, respectively. (d) WCA of SHPL coating after heating resistance test at 120 °C, 160 °C, 200 °C, 240 °C, 280 °C for 1.5 h. (e) Aging resistance of organic and inorganic hybrid super hydrophilic anti-fog coating. Inset is a photo of the appearance of the coating after 50 days of aging resistance test.