Study of Polyhedral Oligomeric Silsesquioxane-Modified Superwetting Transparent Coating for Anti-Fogging, Stain Resistance, Self-Cleaning and Anti-Biological Application

Abstract

Transparent coatings with superwetting properties (superhydrophilicity or superhydrophobicity) have broad application prospects. Usually, most studies have been carried out separately on superhydrophobic coatings or superhydrophilic coatings. In our work, superhydrophilic transparent coatings were prepared by the four-mercapto and four-polyethylene glycol monomethyl acrylate modified POSS (POSS-(SH)₄-(PEGMA)₄) (designated as I-coating) as well as superhydrophobic transparent coating (designated as O-coating) were prepared with the mercapto and seven-heptyl decafluoroheptyl acrylate modified POSS (POSS-SH-(DFMA)₇). The similarities and differences in anti-fogging, stain resistance, self-cleaning and anti-biological application between superhydrophobic and superhydrophilic coatings were compared systematically. The results show that superhydrophilic coatings performed better at preventing fog and facilitating self-cleaning; nevertheless, superhydrophobic coatings exhibited superior efficacy in the removal of contaminants such as markers and lipsticks. Both superwetting coatings demonstrated proficiency in self-cleaning and in deterring biological adhesion with respect to low-viscosity oil droplets. The relevant research of this paper provided a reference for the subsequent study on the advantages and disadvantages of superhydrophilic and superhydrophobic as well as its specific application.

1. Introduction

Superwetting surfaces generally refer to surfaces with superhydrophobic or superhydrophilic properties [1,2]. When the contact angle of a surface > 150° and the rolling angle < 10°, the surface is viewed as a superhydrophobic surface, while superhydrophilic surface refers to a contact angle < 10° [3,4]. Current research on anti-fogging [5,6], self-cleaning [7,8], ice delay [9], anti-biological adhesion [10,11,12], and oil–water separation [13,14] is usually focused on either superhydrophobic coatings or superhydrophilic coatings. Taking anti-fogging applications as an example, superhydrophilic or even hydrophilic surfaces can cause water droplets to quickly spread into a thin film to prevent fogging, thus effectively preventing light reflection and scattering on the surface [15,16]. Superhydrophobic surfaces, however, allow water droplets to roll off rapidly due to their large contact angles and small rolling angles, especially at certain inclinations, thus effectively preventing fogging. For self-cleaning performance, superhydrophilic surfaces can easily form a water film that can wash away pollutants adhered onto the substrate surface. Power et al. [17] prepared a superhydrophobic self-cleaning hard coating using the sol–gel method, which maintained high light transmittance for 70 days and could be used in high-temperature and high-humidity environments. Iman et al. [18] prepared a paraffin-PDMS superhydrophobic coating on solar panels with excellent self-cleaning properties, improving the efficiency of photovoltaic panels by about 14%. Superhydrophobic surfaces with extremely low surface adhesion make it difficult for pollutants to adhere or, if they do, they are easily washed away by water droplets. Luo et al. [19] prepared a moth-eye-inspired superhydrophilic anti-reflection coating with excellent sand removal and self-cleaning capabilities. Thompson et al. [20] demonstrated that the superhydrophilic coating had significant surface dust removal effects through rain exposure tests. In these research studies, the critical materials and preparations to achieve superhydrophilicity or superhydrophobicity are different. Whether superhydrophilic or superhydrophobic coatings provide better anti-fogging or self-cleaning effects is not clear. For certain substrates, it is beneficial to compare anti-fogging, stain resistance, self-cleaning and anti-fogging effect of superhydrophobic or superhydrophilic coatings which are prepared by the identical critical material in order to confirm the appropriate coatings for industry application.

Polyhedral oligomeric silsesquioxanes (POSS) is a cage-like nanoparticle. Its core is an inorganic silicon oxide skeleton, specifically in the form of Si-O-Si, and its eight corner groups R can be modified by various types of organic functional groups [21,22,23]. The polycarbonate (PC) structure contains flexible carbonate chains and rigid benzene rings, offering excellent high light transmittance, impact resistance, easy processing with dimensional stability, and low density. PC is primarily used in electronics, automotive, aviation, construction, healthcare, and other fields, making it an essential high-performance material in industrial applications [24]. Using PC as the substrate and carrying out special wetting treatment on its surface can further expand its application in the requirements of superhydrophilic or superhydrophobic. Compared with similar transparent substrates, the interference of substrate factors can be excluded and the differences between the two coatings in these key properties can be accurately judged. In our work, the corner groups of POSS were modified by hydrophilic groups or hydrophobic groups, respectively, to prepare according superhydrophobic or superhydrophilic coatings. Anti-fogging, stain resistance, self-cleaning and anti-biological properties were studied under the consistent tests. All the coatings showed great transparencies which could be applied to transparent optical components. If anti-fogging, stain-resistant, self-cleaning and anti-biological functions are required, the coating needed can be directly selected from the study.

2. Experimental Section

2.1. Materials

All chemicals were used as received without any further purification. PC with thickness of 0.8 mm was purchased from Sichuan Longhua Photoelectric Film Co. Ltd, (Mianyang, Chian) The PC was used as substrate material. 2-methyl-4-methyl thio-2-morpholine phenylacetone (2-M-4-MT-2-MP, product name I-907, 98%) was purchased from Shanghai Aladin Biochemical Technology Co. Ltd. (Shanghai, China). Decafluorooctyl methacrylate (DFMA) was purchased from Shangfluoro Technology Co., Ltd. (Shanghai, China). Anhydrous tetrahydrofuran (THF, 98%), anhydrous ether and anhydrous ethyl alcohol (EtOH, 99.5%) were purchased from Sinopharm Chemical Reagents Co., Ltd. (Shanghai, China). 1,6-Hexanediol diacrylate (HDDA) was purchased from Eternal Chemical Co. Ltd. (Suzhou, China). Polyethylene glycol monomethyl acrylate (PEGMA, molecular weight 475) and poly(ethylene glycol) dimethacrylate (PEGDMA, molecular weight 600) were purchased from Shanghai Aladin Biochemical Technology Co. Ltd. (Shanghai, China). Silicone-modified polyurethane acrylate (EB 8890) was purchased from Zhanxin Resin (China) Co., Ltd. (Shanghai, China). POSS-SH₈ was synthesized and purified independently [25]. Marker was purchased from Shanghai Chenguang Stationery Co., Ltd. (Shanghai, China). Lipstick was purchased from Guangzhou Kadi Lian Cosmetics Technology Co., Ltd. (Guangzhou, China). Hydrophilic silica (Aerosil^® 200) was purchased from Evonik Industries AG. Hydrophobic silica (Aerosill^® R972) was purchased from Evonik Industries AG. (Shanghai, China). Kitchen heavy oil was obtained from the oil collection box of the kitchen range hood. The Top10 strains of Gram-negative Escherichia coli were obtained from Beijing Baioubowei Biotechnology Co., Ltd. (Beijing, China).

2.2. Preparation Process

2.2.1. Preparation of POSS-SH₄-(PEGMA)₄

PEGMA (8.237 g, 0.01735 mol) was dissolved in 20 mL of THF, designated as solution A. POSS-SH₈ (6.00 g, 0.00446 mol) was weighed and dispersed in 15 mL of THF, followed by the addition of I-907 (0.06 g), forming solution B. Solution A was gradually added to solution B at a rate of 10 mL/h. After the addition was complete, the reaction mixture was stirred for an additional 30 min. The resulting mixture was then filtered through a polytetrafluoroethylene (PTFE) membrane to remove insoluble substances. Partial solvent removal was performed using rotary evaporation at 35 °C. The remaining solution was transferred to a centrifuge tube and centrifuged at 8000 r/min for 10 min using EtOH as the precipitating agent. A white waxy substance settled at the bottom, the target product remained in the intermediate layer, and THF formed the supernatant. The target product was carefully extracted and washed 5–8 times with EtOH to remove residual I-907. Finally, EtOH was evaporated under vacuum at 30 °C for 24 h, yielding a faint yellow viscous product with a yield of 73.5%. The product is POSS-SH₄-(PEGMA)₄.

2.2.2. Preparation of POSS-SH-(DFMA)₇

DFMA (20.8 g, 0.05196 mol) was dissolved in 60 mL of THF, designated as solution C. POSS-SH₈(12 g, 0.00867 mol) and I-907(0.15 g, 0.0006 mol) were dispersed in 50 mL THF to form solution D. Add solution C to solution D at a flow rate of 20 mL/h, and continue the reaction for another 30 min after completion. Partial solvent removal was performed using rotary evaporation at 35 °C. The remaining solution was transferred to a centrifuge tube and centrifuged at 8000 r/min for 10 min using EtOH as the precipitating agent. A white powder settled at the bottom, the target product remained in the intermediate layer, and the supernatant was EtOH/THF. The target product was carefully extracted and washed 5–8 times with EtOH to remove residual I-907. Finally, EtOH was evaporated under vacuum at 60 °C for 24 h, yielding white powder of POSS-SH-(DFMA)₇ with a yield of 76.6%.

2.2.3. Preparation of the Coatings

The protective films on both sides of the substrate (PC) were cleaned by EtOH to remove the contaminants on surface and dried as the substrate.

A mixture (I-coating) of PEGDMA:POSS-(SH)₄-(PEGMA)₄:I-907:HDDA (27:73:10:5 of weight ratio) was spread on the clean PC board by a scraper coating machine. Cured under a 3000 W mercury lamp for 30 s, with a curing energy of approximately 1000 mJ/cm², to obtain a PC sample with I-coating film named as I-coated PC.

A mixture (O-coating) of EB 8890:POSS-SH-(DFMA)₇:I-907:HDDA(76:24:5:5 of weight ratio) was diluted with THF of 10 times weight, and then was stirred under ultrasonic conditions for half an hour. Then EtOH with 30% of the liquid volume was added into the mixture and dispersed under stirring and ultrasonic conditions for another half an hour. A nozzle with a diameter of 0.5 mm, a flow rate of 0.25 mL/s, 0.3 MPa pressure, and a distance of 22–25 cm from the PC board substrate was used to spray onto the PC substrate surface. After standing at room temperature for 3 min, it was placed in a 45 °C oven for about 3 min for further drying treatment. Curing takes place under a 3000 W mercury lamp for 30 s, with a curing energy of approximately 1000 mJ/cm², to obtain a PC sample with O-coating film coating named as O-coated PC. The structural analysis of POSS-(SH)₄-(PEGMA)₄ and POSS-SH-(PEGMA)₇ and the schematic characterization of the coating before and after curing, were shown in the contents of Supplementary Information Sections S1 and S5.

2.3. Characterization

2.3.1. Surface Wettability

The surface wettability behavior of the coating was evaluated by measuring the water contact angle (WCA) using a contact angle measurement system (DSA30, KRÜSS, Hamburg, Germany). Measurements were performed at room temperature using deionized water. A droplet volume of 5 μL was consistently maintained, and the droplet was dispensed at a controlled rate of 2 μL/s. For each sample, measurements were taken at five different locations to ensure accuracy, and the average WCA value was reported.

2.3.2. Transmittance

The transmittances of PC, I-coated PC and O-coated PC were measured using a UV–visible spectrophotometer (UV3200, Shanghai Mepuda Instrument Co., Ltd. Shanghai, China) in the range of 300–800 nm. The comprehensive light transmittance and haze values of the samples were directly measured using a light transmittance-haze meter (SGW-820, Shanghai Yidian Physical Optical Instrument Co., Ltd. Shanghai, China).

2.3.3. Scanning Electron Microscopy (SEM)

The surface of the coating sample was treated with gold spray, and the surface microstructure morphology was observed by SEM (SU8010, HITACHI, Tokyo, Japan) under the accelerated voltage of 15 kV. Before the test, the surface of the sample was treated with gold coating at the nanometer level in vacuum.

2.3.4. Modeling of Water Droplets on the Surface of the Coating

Before constructing the water drop model, a water box must be generated. The Amorphous Cell module was used to build the box, 1000 water molecules were input into the box, the density was set to 1.0 g/cm³, and the COMPASS force field was used to build it. The initial box model was geometrically optimized by the steepest descent method with 50,000 steps, energy convergence standard of 0.001 kcal/mol and force convergence standard of 0.5 kcal/mol/Å. Then the geometrically optimized water box was balanced in a regular ensemble (NVT). The Berendsen temperature control method was used, the temperature was 25 °C, and the equilibrium time was 100 ps. The initial velocity of water molecules was set to random. After the NVT balance was completed, nanocluster was selected in the Build Nanostructure option, and the droplet diameter was 1.5 nm. The coating models were constructed and molecular dynamics calculations were performed using the molecular dynamics software Material Studio 2017.

2.3.5. Anti-Fogging

The anti-fogging performances of the coatings were assessed by exposing the I-coated PC, O-coated PC and uncoated PC samples to hot vapor. We placed a 2 cm × 6 cm square sample on top of a glass dish containing 100 °C, 75 °C, and 50 °C hot water, 5 cm apart from the water surface. We observed and photographed the sample surfaces and tested the transmittance and haze value of the relevant sample.

2.3.6. Stain Resistance

We cut out 2 cm × 6 cm rectangular sample strips and drew an “8” shape on the sample surfaces with a marker. We observed the completeness or contraction of the mark. After 5 s, wipe the surface with a lint-free cloth by a load of 100 g weight to test if the surface could be wiped clean. If the mark could be removed, repeated drawing was done at the same location until the mark on the coating surface could not be wiped away. The number of wipes was considered as representing the stain resistance ability of the mark ink.

Circles were drawn on the sample surfaces three times with lipstick; then, the drawn surface was wiped with a lint-free cloth by a load of 100 g weight to observe the residue left after wiping. The transmittance and haze values of the relevant samples were measured at each test.

2.3.7. Self-Cleaning

In order to simulate the self-cleaning performance under rainwater flushing, hydrophilic silica or hydrophobic silica with particle sizes around 3 μm as contaminants were distributed on the surfaces of PC, I-coated PC and O-coated PC. The weight of silica powder was 0.1 g. The samples of 2 cm × 6 cm were tilted at an angle of 30°. Then, deionized water drops were dripped from the top of the powder at a height of about 3 cm. After flushing, the residual contaminants on the coating surface were baked for 30 min at 60 °C. The pollutant removal rate R was calculated by Formula (1) to characterize the self-cleaning ability of dirt.

$$\mathrm{R}={\displaystyle \frac{{\mathrm{m}}_1-{\mathrm{m}}_2}{{\mathrm{m}}_1}}\times 100\mathrm{\%}$$

(1)

m₁ and m₂ are the mass of hydrophilic silica or hydrophobic silica spreading on the surface and after baking, respectively.

In order to simulate the self-cleaning ability of oil-like substances, silicone oil containing carbon black and heavy oil residue from range hoods were used as two kinds of oil contaminant. In this test, the rectangular sample strips measuring 2 cm × 6 cm were cut and tilted at a 30° angle. Oil contaminant of 0.1 mL was dripped onto the surface, then, three drops of deionized water were dripped from the top of the oil contaminant at a height of about 1 cm.

2.3.8. Anti-Biological Application

PC, I-coated PC and O-coated PC were cut into 1 cm × 1 cm strip samples and incubated at 37 °C in a 2 mg/mL bovine serum albumin (BSA, biotech grade, Aladdin, Shanghai, China) ultra-pure water solution in a constant temperature shaking incubator for 2 h at a shaking speed of 100 rpm. Then, we transferred the samples to a centrifuge tube after ultrasonication in a 1% sodium dodecyl sulfate (SDS, Coriell) solution for 3 min to separate proteins absorbed from the sample surface. Finally, we determined the protein concentration in the above-mentioned centrifuge tube using a protein assay kit (Broadford).

According to the bacterial adhesion test method in reference [26], the antibacterial adhesion performance of superwetting coating was evaluated using the Top10 strain of Gram-negative Escherichia coli (E. coli for short), and the antibacterial adhesion rate (E_b) was calculated under the comparison between superwetting coatings and PC substrate. The calculation Formula (2) is as follows:

$${\mathrm{E}}_{\mathrm{b}}={\displaystyle \frac{{\mathrm{N}}_{\mathrm{b}}-{\mathrm{N}}_{\mathrm{c}}}{{\mathrm{N}}_{\mathrm{b}}}}\times 100\mathrm{\%}$$

(2)

N_b and N_c were the number of bacterial colonies corresponding to PC substrate and superwetting coatings, respectively. Specifically, the “zone counting method” was employed: the plate was divided into six zones, and the colonies were directly observed and counted with the naked eye, followed by summing up the counts from each zone.

3. Results and Discussions

3.1. Surface Structure, Wettability and Transmittance

The SEM and WCA of PC substrate and the coatings are shown in Figure 1. The WCA of the uncoated blank PC was 82.5°. The WCA value of the I-coated PC surface was 7.8°, confirming its superhydrophilicity. The WCA value of O-coated PC surface was 160.1°, confirming its superhydrophobicity. The superhydrophilic origin of I-coated PC was mainly due to the large number of hydrophilic polyether segments in the coating. In addition, hydrophilic modified POSS could migrate onto the surface to form a certain rough structure, which further reduces the WCA value of the coating according to Wenzel wetting theory [27]. Due to the low surface energy of F atoms, which were included during O-coated PC preparation and the migration of hydrophobic modified POSS onto the surface, O-coated PC exhibited superhydrophobic properties [28].

Although the light transmittance of the smooth PC substrate reached 89%, there were still some defects on the surface (Figure 1a), which was caused by insufficient melting during the extrusion process of the PC board. There were some granular structures on the surface of I-coated PC (Figure 1b), which was the result of the diffusion and agglomeration of hydrophilic POSS to the surface during the heating process before curing. In addition, because PEGMA and the main film-forming substance PEGDMA in hydrophilic modification both have ethoxy groups and were structurally similar, according to the principle of similar compatibility, the boundary between the agglomeration and the substrate was not particularly obvious. This relatively uniform structure did not cause obvious absorption and reflection of light, and the transmittance reached 87.0%. Figure 1c showed that the surface of the O-coated PC formed a rough structure formed by the accumulation of fine particles. The diameter of these particles was 20–50 nm, and these particles were adhered to each other and piled up into protrusions less than 200 nm. At the same time, the average diameter of the formed holes was also within 150 nm. The nanostructure was beneficial to weaken the scattering of light on its surface and achieved the effect of increasing transmittance and reducing reflection to a certain extent. Since the coating was not a uniform coating in composition and thickness, there were also adverse effects, such as light absorption, resulting in the overall transmittance of O-coated PC being 85.6%, which still showed good transmittance. Figure 1d shows the average transmittances of blank PC, I-coated PC and O-coated PC. Data of water spreading, haze and gloss of I-coated PC, O-coated PC and PC were shown in Supplemental Information Sections S2 and S6 respectively.

3.2. Construction of Water Droplet on Coating Surface Model

Firstly, the interaction between water molecules and PEGMA molecules was simulated by NVT molecular dynamic relaxation method, and then the distribution of water molecules in PEGMA was systematically analyzed. Figure 2a shows the hydrogen bond structure inside the simulated box, in which the hydrogen bonds were mainly divided into the hydrogen bond between water molecules and the hydrogen bond between water molecules and PEGMA hydrophilic chain segments. The radial distribution function shows two peaks in the 1.9–2.1 Å interval (Figure 2b), which reflected the existence of intermolecular hydrogen bonding. In other words, hydrogen bonds occurred between the hydrogen atoms in water molecules and the oxygen atoms in PEGMA. As shown in Figure 2c, when the water droplet comes into contact with the surface of I-coated PC, the water molecules formed hydrogen bonds with the ethoxy group in the coating, thus forming a new interface with lower interfacial energy, resulting in the rapid spreading of the water droplet. There was a significant spread phenomenon after 50 ps. The spreading state of the water droplet between 200 ps and 500 ps was basically the same, and it did not penetrate into the coating, which was due to the water resistance of the inorganic structure with POSS. As can be seen from Figure 2d, there were a large number of fluorocarbon segments on the surface of O-coated PC. Due to the stable physical and chemical properties of fluorocarbon segments, the hydrophobic surface was endowed with extremely low surface energy. The shape of the water droplet changed little during the NVT molecular dynamics simulation from 10 ps to 500 ps.

In order to further verify the mechanism of superhydrophobicity, Cassie–Baxter Equation was used [29]:

$$\cos \mathrm{s}{\theta }^{*}=f_s\ast (1+\cos \theta )-1$$

(3)

In Formula (3) ${\theta }^{*}$ was the apparent contact angle (${\theta }^{*}$ = 160°),   $\theta$ was the intrinsic contact angle of water on an ideal solid surface ($\theta$ = 120°),   $f_s$ was the solid-liquid contact fraction.It was calculated that $f_s$ = 0.12 by Formula (3), which indicated that 88% of the water droplets were in contact with the air on the O-coated PC surface. A large amount of air formed an “air cushion” to lift the water droplets, which was the key to the formation of superhydrophobic surface. This also showed that the O-coated PC superhydrophobic surface was in line with the Cassie–Baxter model.

3.3. Anti-Fogging Performance

An increase in ambient relative humidity leads to the formation of numerous condensed water droplets on solid surfaces. The existence of water droplets causes the fogging phenomenon and refraction and scattering effects of light, which decreases the transparency and visibility [30]. In our work, the coatings were exposed to increased ambient relative humidity resulting from 100 °C, 75 °C, and 50 °C of hot water. The anti-fogging performances were confirmed by observing transparency and visibility of the coatings.

Prior to the test, the fonts at the bottom of all three samples could be clearly observed (Figure 3a). Above 100 °C hot water, both superhydrophilic I-coated PC and superhydrophobic O-coated PC exhibited significant anti-fogging effects as shown in Figure 3b. The anti-fogging mechanisms of the two coatings are different. The I-coated PC reduces water droplet reflection by promoting rapid spreading of water droplets on its surface. Whereas O-coated PC causes fog to condense into larger droplets, which, under the dual effect of the superhydrophobic surface and gravity, quickly roll off, preventing adhesion of water droplets to the surface and thus achieving the anti-fogging effect. Under this condition, the light transmittance and haze of I-coated PC, PC, and O-coated PC were 85.7%, 72.2%, 83.5% and 1.1%, 20.4%, 5.5%, respectively. It was evident from the PC substrates in Figure 3b–d that as the temperature decreases, the fog droplets that were formed by water vapor condensation gradually decreased in size, possibly because at higher temperatures, small fog droplets tended to coalesce into larger ones. As shown in Figure 3c, above 75 °C hot water, I-coated PC still maintained a significant anti-fogging performance, but the superhydrophobic surface of O-coated PC began to be covered by a few droplets, leading to a noticeable decrease in transparency. The light transmittance and haze of I-coated PC, PC, and O-coated PC were 83.6.7%, 62.8%, 70.7% and 1.9%, 31.8%, 17.5%, respectively. This is because water vapor at 75 °C condenses into smaller droplets than at 100 °C. Smaller droplets are more likely to adsorb onto the surface, leading to localized weakening of superhydrophobic properties. As shown in Figure 3d, as the temperature dropped to 50 °C, the superhydrophilic I-coated PC still maintained good transparency, while the superhydrophobic O-coated PC almost lost its anti-fogging performance, making it impossible to identify the reference object at the bottom. Under this condition, the light transmittance and haze of I-coated PC, PC, and O-coated PC were 81.4%, 60.2%, 56.8% and 2.7%, 50.5%, 45.3%, respectively. The anti-fogging performance of O-coated PC superhydrophobic surface deteriorates or disappears was caused by the Cassie–Baxter state changed to the Wenzel state under the impact of water vapor [31,32]. Additionally, under three different temperature conditions, the PC substrate surfaces without superwetting properties were fogging due to the water droplets’ adhesion of varying sizes.

3.4. Stain Resistance

In Figure 4a, no significant contraction of the marks was observed on both the superhydrophilic I-coated PC and the PC substrate after drawing “8” shape. Notably, the edge of the mark on I-coated PC (Figure 4b) was more sharply than that on PC (Figure 4c), indicating their different wetting performances. The mark on the superhydrophobic O-coated PC appeared as discontinuous small droplets (Figure 4d), which could be easily removed with a lint-free cloth. As shown in Figure 4e, after wiping 20 times, only a few markers remained on the surface of O-coated PC. This indicated that the superhydrophobic coating demonstrated excellent stain resistance of marker ink, whereas the superhydrophilic coating performed poor stain resistance of marker ink.

In the field of display technology, especially in personal mobile display devices, transparent plastic materials inevitably come into frequent contact with cosmetics. This study uses lipstick as a model to evaluate the resistance of cosmetic stains. After the drawing of lipstick on the I-coated PC, O-coated PC and PC substrates (Figure 5a), five wipes with lint-free cloth were performed (Figure 5b). It could be found that lipstick residue could be viewed on I-coated PC and PC as shown in Figure 4b. In contrast, the super-hydrophobic O-coated PC showed almost no residue after wiping under the same conditions. Since the components of lipstick are mineral oil, natural oils, waxes and so on, the above result indicates that hydrophilic coatings and PC substrates have poor stain resistance. The superhydrophobic surface usually exhibited low surface energy [27,31] and thus weaker adhesion to the main components of lipstick leading to significant stain resistance.

The WCA of I-coated PC, PC and O-coated PC where the surfaces of the lipsticks were wiped was 76.3°, 92.5°, and 127.9°, respectively, indicating that the superwetting properties of I-coated PC and O-coated PC disappeared completely. The surface of the lipsticks after wiping was observed using an optical microscope, as shown in Figure 4c. From Figure 5c, it could be seen that the surface of I-coated PC was covered with a thin and uniform layer of oily substance, the PC substrate was covered with thicker layers of oily residues, and O-coated PC surface had a very small number of oil-like stains. Following each test, a new lint-free cloth was used for subsequent measurements, and this cycle was repeated three additional times. After these three cycles, no visible lipstick marks were observed on the I-coated PC surface, with the corresponding water contact angles recorded as 52.5°, 34.7°, and 30.8°, respectively. For the O-coated PC surface, the contact angles measured over these three testing cycles were 138.7°, 143.5°, and 143.8°, sequentially. Due to the decreased superwetting property and residual stains, it is suggested that the stain resistance of the superhydrophobic coating might decrease over long-term contact with lipsticks. The values of Transparency (T) / Haze (H) during the lipstick test were detailed in Section S4 of the supplementary information.

3.5. Self-Cleaning

From Figure 6a, it could be seen that the hydrophilic silica powder completely fell off from both the superhydrophobic O-coated PC and the superhydrophilic I-coated PC, demonstrating excellent self-cleaning performance. The pollutant removal rate R of the hydrophilic silica powder from the superhydrophilic I-coated PC was 99.2% and the used volume of water was only 15 mL. In contrast, after using 20 mL of water, the pollutant removal rate R for the superhydrophobic O-coated PC was 90.8% and some streaks on the coating surface were left. When the droplet volume reached 25 mL, the pollutant removal rate R of O-coated PC is 99.5% (Figure 6b). However, for the PC substrate without superwetting property, most of the powder remained on the surface except for a small portion that was washed away by water (R = 25.5%), thus failing to achieve self-cleaning (Figure 6b). The observed differences during test process were significant. For I-coated PC, no silica powder fell off until the total droplet volume reached 3 mL. At beginning of the test, they were wetted by water. As more water was added, the hydrophilic silica powder slid off. For O-coated PC, however, the hydrophilic silica powder adhered to spherical water droplets and rolled off directly. This indicates that the superhydrophilic I-coated PC allows water droplets to wet the surface and form a water film, which promotes the direct sliding of pollutants as it flows downward (Figure 6c,d). On the other hand, the superhydrophobic O-coated PC causes the pollutants to roll off with the droplets through spherical water droplets bouncing, leaving the pollutants on the coating as tear-like stains (Figure 6e,f).

Using the hydrophobic silica powder to repeat the above test. The results are shown in Figure 7a–c. Only 5 mL of water was needed to rinse the hydrophobic silica powder clean from the superhydrophilic I-coated PC, with a pollutant removal rate R of 99.0% (Figure 7b). Whereas 35 mL of water was needed to wash away most of the pollutants from the superhydrophobic O-coated PC. It could be seen in Figure 7c that some residual was still on the surface and the pollutant removal rate R was 93.6%. For PC substrates without any superwetting coatings, even with 30 mL of water, the pollutant removal rate R was only 20.3%. Most of pollutants still remained on the surface. For the I-coated PC, water droplets can quickly penetrate beneath the silica powder and form a water film, lifting the silica powder to slide off (Figure 7d,e). For the O-coated PC, spherical water droplets act like icebreakers, pushing the silica powder to the sides, while some of the silica powder is directly pushed to the bottom by the water droplets (Figure 7f,g), resulting in less powder adhering to the spherical water droplets.

In the oil removal self-cleaning test, about 0.1 mL of silicone oil containing carbon black was dropped onto three surfaces (Figure 8a). The results showed that the oil droplets on the superhydrophobic O-coated PC exhibited slight contraction, while those on the superhydrophilic I-coated PC showed no significant changes. However, oil droplets wetted the PC substrate easily. Under the effect of three water droplets (Figure 8b), the hydrophilic I-coated PC quickly absorbed and formed a film. Due to the higher density of water compared to silicone oil and the strong adsorption of the coating to water, these liquids could float on the water film and slip off the surface of I-coated PC within 2 s (Figure 8c). On the superhydrophobic O-coated PC, three water droplets lifted the silicone oil droplet and rolled off, reaching the lowest point of the O-coated PC sample in 4 s (Figure 8c). On the PC substrate, the oil droplet was in a wetted state, thus water droplets could not penetrate the interface between the oil droplet and the PC substrate. PC substrate was easily contaminated by oily pollutant which was similar to silicone oil.

3.6. Anti-Biological Application

The results of protein adhesion resistance are shown in Figure 9. The original experimental data for the anti-biological applications were shown in Section S3 of the supplementary information. On the PC substrate, the adsorption concentration of protein was 0.69 mg/mL. In contrast, the protein adsorption concentrations on the superhydrophilic I-coated PC and the superhydrophobic O-coated PC decreased to 0.25 mg/mL and 0.33 mg/mL, respectively, demonstrating significant anti-protein adsorption properties. Further analysis revealed that the superhydrophilic I-coated PC performs better anti-protein adsorption than the superhydrophobic O-coated PC. This phenomenon can be attributed to the hydrogen bonding formed between the superhydrophilic I-coated PC surface and water molecules in an aqueous environment, leading to the formation of a hydration layer and a macroscopic water film. These factors create physical and energetic barriers to exclude protein adsorption, endowing I-coated PC with excellent anti-protein adsorption performance [33,34]. The anti-protein adsorption capability of the superhydrophobic O-coated PC mainly stems from its extremely low surface energy and the dense air film layer formed by the superhydrophobic surface, which significantly reduces the protein adhesion.

As shown in Figure 10, the number of adhering E. coli was significantly higher on PC substrates without superwetting treatment. In contrast, it was observed that the number of E. coli adherences had markedly decreased on the surfaces of I-coated PC and O-coated PC. Through precise counting methods, we found that the antibacterial adhesion rates for superhydrophilic I-coated PC and superhydrophobic O-coated PC reached impressive levels of 95% and 93%, respectively. Similar to the mechanism of protein adsorption resistance, the excellent antibacterial adhesion performance of I-coated PC is mainly attributed to the water film formed on its hydrophilic surface. This water film effectively isolates bacteria from direct contact with the surface of PC substrate, making it difficult for bacteria to adhere to the superhydrophilic layer under oscillation conditions. On the other hand, superhydrophobic O-coated PC, due to the air layer retained on its rough surface structure, effectively blocks the contact between bacterial solutions and the substrate surface. Even if there is some contact, the low surface energy of the O-coated PC surface significantly inhibits the stable growth of bacteria, thus demonstrating superior antibacterial adhesion properties.

4. Conclusions

The superhydrophilic coating and superhydrophobic coating prepared modified the functional group of POSS by hydrophilic and hydrophobic group, respectively. When water droplets encounter the superhydrophilic coating, they quickly form a water film, reducing the diffuse reflection of light and providing excellent anti-fog performance at temperatures of 100 °C, 75 °C, and 50 °C, while the superhydrophobic coating only showed good anti-fog performance at 100 °C. Comparison of ink resistance and cosmetic resistance showed that the self-cleaning or easy wiping properties of the superhydrophilic coating was worse than that of the superhydrophobic coating. Dust removal and self-cleaning tests showed that the water film formed on the surface of the superhydrophilic coating can easily rinse off both hydrophilic and hydrophobic fumed silica from the surface, demonstrating excellent self-cleaning performance, while the superhydrophobic coating was relatively weaker. For low-viscosity silicone oil, the superwetting surfaces all exhibit good oil-removal and self-cleaning effects. Regarding bioadhesion, both types of coatings exhibit excellent performance because their water and air films prevent E. coli from adhering to their surfaces. In short, I-coating has a more excellent performance in areas such as frequent rain or fog occurrence and medical intervention treatment. However, in the field of anti-graffiti, waterproofing and oil resistance, O-coating shows superior performance.