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Article

Application of High-Surface Tension and Hygroscopic Ionic Liquid-Infused Nanostructured SiO2 Surfaces for Reversible/Repeatable Anti-Fogging Treatment

by
Satoshi Nakamura
1,2,
Jerred Wassgren
1,
Sayaka Sugie
3 and
Atsushi Hozumi
1,*
1
National Institute of Advanced Industrial Science and Technology (AIST), 4-205, Sakurazaka, Moriyama, Nagoya 463-8560, Japan
2
Research Institute for Electronic Science, Hokkaido University, Kita 21, Nishi 10, Kita-ku, Sapporo 001-0021, Japan
3
Department of Life Science and Applied Chemistry, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan
*
Author to whom correspondence should be addressed.
Surfaces 2024, 7(3), 482-492; https://doi.org/10.3390/surfaces7030031
Submission received: 13 May 2024 / Revised: 18 June 2024 / Accepted: 28 June 2024 / Published: 2 July 2024
(This article belongs to the Special Issue Surface Modification and Coating to Improve Properties of Various Materials)
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Abstract

:
Anti-fogging coatings/surfaces have attracted much attention lately because of their practical applications in a wide variety of engineering fields. In this study, we successfully developed transparent anti-fogging surfaces using a non-volatile and hygroscopic ionic liquid (IL), bis(hydroxyethyl)dimethylammonium methanesulfonate ([BHEDMA][MeSO3]), with a high surface tension (HST, 66.4 mN/m). To prepare these surfaces, a layer of highly transparent, superhydrophilic silica (SiO2) nano-frameworks (SNFs) was first prepared on a glass slide using candle soot particles and the subsequent chemisorption of tetraethoxysilane (TEOS). This particulate layer of SNFs was then used as the support for the preparation of the [BHEDMA][MeSO3] layer. The resulting IL-infused SNF-covered glass slide was highly transparent, superhydrophilic, hygroscopic, and had self-healing and reasonable reversible/repeatable anti-fogging/frosting properties. This IL-infused sample surface kept its excellent anti-fogging performance in air for more than 8 weeks due to the IL’s non-volatile, HST, and hygroscopic nature. In addition, even if the water absorption limit of [BHEDMA][MeSO3] was reached, the anti-fogging properties could be fully restored reversibly/repeatably by simply leaving the samples in air for several tens of minutes or heating them at 100 °C for a few minutes to remove the absorbed water. Our IL-based anti-fogging surfaces showed substantial improvement in their abilities to prevent fogging when compared to other dry/wet (super)hydrophobic/(super)hydrophilic surfaces having different surface geometries and chemistries.

Graphical Abstract

1. Introduction

Anti-fogging coatings/surfaces for transparent objects, such as eyeglasses, vehicle windshields, mirrors, camera lenses, solar cells, medical/analytical instruments, and other industrial equipment, have recently gained considerable attention because of their ability to prevent the formation of condensed water droplets and therefore reduce visible light scattering, leading to an increase in visibility, driving/operation safety, and device performance [1,2,3]. To prevent fogging, very hydrophilic or superhydrophilic surfaces (static water contact angles (CAs, θS) of less than 20° or 5°, respectively) are preferred, rather than superhydrophobic ones (θS of water over 150°). On (super)hydrophilic surfaces, condensed water droplets tend to rapidly spread and form into a transparent thin water layer, rather than form droplets (avoiding formation of fog) [1,2,3]. This thin water layer effectively suppresses light scattering, improving visibility. Superhydrophobic surfaces, on the other hand, cause water droplets to nucleate within surface textures under high humidity conditions. These surface geometries reduce the mobility of water droplets and can lead to surface flooding [4,5]. In addition to having a (super)hydrophilic nature, being hygroscopic is also an important factor to achieve long-lasting anti-fogging performance by preventing excess and inhomogeneous water condensation under harsh fogging conditions [6,7,8,9].
A wide variety of materials, including hydrophilic polymers/polymer brushes and self-assembled monolayers having oxygen-containing functional or zwitterionic groups [10,11,12,13,14,15,16,17,18], and inorganic nanoparticles (titanium dioxide (TiO2) [19,20,21,22,23,24], zinc oxide (ZnO) [25], silica (SiO2) [10,12,13,20,22,23,26,27,28,29,30], and zeolite [31,32,33,34]), and coating techniques, including spin coating [28,33,34], dip coating [27,29,31], layer-by-layer assembly [10,12,13,20,23,26,30], spray coating [22,32], and chemical vapor deposition [35], have been explored to fabricate anti-fogging coatings/surfaces so far. Although these conventional (super)hydrophilic coatings/surfaces initially display excellent anti-fogging properties, they are easily contaminated due to their high surface energies, causing their anti-fogging properties to eventually deteriorate [36]. Therefore, self-cleaning/anti-fouling properties are required to prolong surface wetting properties, such as those derived from the photocatalytic degradation abilities of metal oxides like TiO2 and ZnO [19,22,24,27] or the low surface energies of perfluoroalkyl groups [37,38]. Additionally, as most of the anti-fogging coatings/surfaces reported so far typically lack self-healing properties, such coatings/surfaces immediately and permanently lose their functional properties once they are physically/chemically damaged, which greatly limits their practical applicability. For example, if such conventional coatings/surfaces are physically damaged, the damaged areas may serve as nucleation sites of water droplet formation, resulting in the deterioration of anti-fogging properties. Thus, the development of highly transparent, (super)hydrophilic, hygroscopic, and self-healing anti-fogging coatings/surfaces is highly sought after in a wide variety of advanced applications and still very challenging.
In contrast to such solid functional surfaces described above, slippery liquid-infused porous surfaces (SLIPSs) or liquid-infused surfaces (LISs) have self-healing abilities because the intermediate liquid is firmly trapped within the porous structures and forms a stable liquid layer at the topmost surface [39,40]. This lock-in effect allows for the long-term stability of surface properties, which can compensate for the shortcomings of conventional solid functional coatings/surfaces without self-healing abilities. Until now, low-surface tension (LST) liquids, including silicone oils, perfluorinated ethers, vegetable oils, and ionic liquids (ILs), have been widely used as a lubricant for SLIPSs/LISs to endow excellent omniphobic, self-cleaning/healing, anti-icing/frosting, anti-adhesion, anti-bacterial/fouling properties, and so on [41]. On the other hand, there have only been a limited number of papers describing preparation techniques or properties of SLIPSs/LISs using high-surface tension (HST) liquids [41], but such (super)hydrophilic SLIPSs/LISs have attracted much attention lately and been used for water harvesting [42,43], anti-icing [44], and anti-bacterial applications [45].
In this study, we report the fabrication of HST-IL-infused nanostructured SiO2 surfaces showing long-lasting and reversible/repeatable anti-fogging properties for the first time. We used highly transparent and superhydrophilic SiO2 nano-frameworks (SNFs) as support materials to lock in an IL [BHEDMA][MeSO3] (bis(hydroxyethyl)dimethylammonium methanesulfonate: C6H16O2N+CH3SO3). We selected this IL because it is non-volatile, hygroscopic, and has HST (66.4 mN/m). Although the anti-fogging properties of the cleaned superhydrophilic glass slide surfaces with and without SNFs deteriorated within a week or a day, respectively, our IL-infused SNF-covered glass slide surface kept its excellent anti-fogging property in air for more than 8 weeks thanks to our IL’s non-volatile, HST, and hygroscopic nature. In addition, even if the water absorption limit was reached, anti-fogging properties could be fully and reversibly/repeatably restored by simply leaving the samples in air for several tens of minutes or heating them at 100 °C for a few minutes to remove the absorbed water. Furthermore, our [BHEDMA][MeSO3]-infused SNF-covered glass slide surface was also effective in frosting prevention when compared to the superhydrophilic glass slides with and without SNFs. To the best of our knowledge, there have been no studies focusing on fabricating HST and hygroscopic IL-infused coatings/surfaces which show excellent optical properties and anti-fogging/frosting properties that are stable, long-lasting, reversible/repeatable, and self-healing even after being physically damaged. Our anti-fogging coatings/surfaces shown here have significantly improved performance over other dry/wet (super)hydrophobic/(super)hydrophilic surfaces with different surface geometries and chemistries.

2. Materials and Methods

2.1. Materials

Tetraethoxysilane (TEOS) and Trichloro(1H,1H,2H,2H-heptadecafluorodecyl)silane (FAS17) were purchased from FUJIFILM Wako Pure Chemicals Co., Ltd., Osaka, Japan. Bis(hydroxyethyl)dimethylammonium methanesulfonate ([BHEDMA][MeSO3]) was a gift from Prof. Thomas J. McCarthy at the University of Massachusetts, Amherst, MA, USA. 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([EMI][TFSI]) was purchased from Sigma-Aldrich Co., LLC, Burlington, MA, USA. A fluorinated oil (Krytox 103) was purchased from Dupont-Toray, Tokyo, Japan. 3-Aminopropyltriethoxysilane (APTES) was purchased from TCI, Tokyo, Japan. Glass slides (76 mm × 52 mm or 40 mm × 40 mm) were purchased from Matsunami Glass Ind. Ltd., Osaka, Japan. Ultrapure water (18.2 MΩ/cm, Milli-Q, Millipore, Darmstadt, Germany) was used for all rinsing processes and CA measurements.

2.2. Preparation of [BHEDMA][MeSO3]-Infused SNF-Covered Glass Slides

As support materials for HST-IL, we used highly transparent and superhydrophilic SNF-covered glass slides prepared by a “candle soot method”, which was first demonstrated by Deng et al. [46]. First, glass slides (76 mm × 52 mm and 40 mm × 40 mm) were directly exposed to a lit candle while being moved for 90–120 s so that soot particles were homogeneously deposited over the entire surface, as shown in Scheme 1. The soot surfaces were activated by UV/ozone treatment (for 30 min at a residual pressure of 103 Pa). Next, the samples were placed into a clean Teflon® container, together with a 3.5 mL glass vial with the cap off containing 200 μL of neat TEOS solution inside a glove box filled with dry N2 gas (relative humidity (R.H.) of less than 5%) to ensure reproducibility. The Teflon® container was tightly sealed with a cap and heated in an oven maintained at 60 °C, forming a SiO2 shell around the soot by the chemical vapor deposition (CVD) of TEOS. After 3 h, the glass slides were taken out of the container and calcinated at 600 °C for 3 h to remove any organic components including the carbon core, yielding a transparent, SNFs. Finally, HST-IL ([BHEDMA][MeSO3]) was dropped (31.25 μL/cm2) and spin-coated (1000 rpm for 5 s and 2000 rpm for 10 s) onto the SNF-covered glass slides at room temperature in ambient air. Scanning electron microscopy (SEM) images of the sample surfaces were obtained on an S-4500 (Hitachi Ltd., Tokyo, Japan). The optical transparency of some of the samples in the visible wavelength range was measured using a Cary 5000 spectrometer (Agilent Technologies Inc., Santa Clara, CA, USA).

2.3. Preparation of FAS17-Coated and Krytox-Infused SNF-Covered Glass Slides

For control experiments, FAS17-coated and Krytox-infused SNF-covered glass slides were prepared by a slightly modified procedure of our previous study [47]. Briefly, the SNF-covered glass slides were treated with FAS17 in the same procedure as the CVD method described above, except for the oven temperature (150 °C). After 3 h of CVD treatment, they were taken out, rinsed with a copious amount of n-hexadecane and Milli-Q water, and blown dry with a stream of N2. Finally, Krytox was spin-coated onto the FAS17-coated SNF-covered glass slides in the same way described above.

2.4. Preparation of [EMI][TFSI]-Infused SNF-Covered Glass Slides

For control experiments, [EMI][TFSI]-infused SNF-covered glass slides were prepared by a modified procedure of our previous study [48]. Briefly, to adjust the affinity between the SNFs and [EMI][TFSI], SNF-covered glass slides were treated with APTES in the same procedure as the CVD method described above, except with the oven temperature set at 100 °C. After 3 h of CVD treatment, they were taken out, rinsed with a copious amount of Milli-Q water, and blown dry with a stream of N2. Finally, [EMI][TFSI] was spin-coated onto the APTES-coated SNF-covered glass slides in the same way described above.

2.5. Measurements of Static and Dynamic Wettability

θS and dynamic (advancing (θA) and receding (θR)) water CAs and the substrate tilt angle (α) required for water droplets to slide or roll off were collected using a DropMaster DM-501 (Kyowa Interface Science Co., Ltd., Saitama, Japan) at room temperature. θS values were obtained by gently placing a 3 μL water droplet on the horizontal sample surfaces. θA/θR values were measured by adding and removing water from the 3 μL water droplet. In this study, α was defined as the angle at which a 10 μL water droplet moved 0.5 mm while the stage tilts at an angular interval of 1° per 4 s. These measurements were taken at three different points, and the averages (the error was about ±2°) are shown.

2.6. Anti-Fogging Test 1: Cold/Warm Test

For the cold/warm test, glass slides with surface treatment on both sides were used. The samples were placed in a refrigerator at 4 °C for 30 min. Then, they were taken out from the refrigerator, exposed to the ambient atmosphere (≈20 °C and R.H. of 40−50%), and checked above a printed paper to see if the surfaces fogged up. For cyclic tests, the time in the refrigerator was shortened to 10 min.

2.7. Anti-Fogging Test 2: Hot Vapor Test

Sample surfaces were placed upside down at a distance of 2 cm from hot boiling water (80 °C) in a glass vial and held for 1 min. Then, a printed paper was placed under the glass vial to see if the surfaces fogged up.

2.8. Anti-Frosting Test

Three samples (bare, SNF-covered, and [BHEDMA][MeSO3]-infused SNF-covered glass slides) were fixed to a Peltier cooler and cooled to −5 °C under a surrounding temperature of ≈20 °C and R.H. of 40−50%. Then, the process of the frost formation was recorded.

3. Results and Discussion

The preparation procedure for HST-IL ([BHEDMA][MeSO3])-infused SNF-covered glass slides is shown in Scheme 1. In this study, the resultant SNF-covered glass slides were used as is without using any specific surface modification to adjust the affinity between the SNFs and [BHEDMA][MeSO3]. Since the SNFs were superhydrophilic (θS of water: less than 5°), HST-[BHEDMA][MeSO3] preferentially wetted the high-surface energy SNFs. In addition, according to the typical cross-sectional SEM image (Figure S1A), our SNFs with a sufficient thickness (300~1000 nm) and large surface area effectively worked as support materials to stably lock-in HST-[BHEDMA][MeSO3] through an anchor effect. No draining of the infusing [BHEDMA][MeSO3] was visually observed, even when the sample surface was turned upside down. Judging from the optical micrographs and typical UV-vis spectra shown in Figure 1A,B, all SNF samples were highly transparent, but the [BHEDMA][MeSO3] infusion further increased the optical transparency of the SNF-covered glass slide from 87% (before infusion) to 89% (after infusion). This must be due to the suppression of optical reflectance, because [BHEDMA][MeSO3] homogeneously and fully covered the entire surface of the samples (Figure S1B).
We first investigated the surface static/dynamic wetting properties of our samples. For comparison, five samples with different surface physical/chemical properties ((super)hydrophilic or (super)hydrophobic, flat or rough, and dry or wet) were employed. The static/dynamic water CAs (θS/θA/θR) and Δθ/α (measured by 3 μL and 10 μL water droplet, respectively) values of these surfaces are summarized in Table 1. Static water CA measurements confirmed that the UV/ozone-cleaned glass slides with and without SNFs and HST-[BHEDMA][MeSO3]-infused SNF-covered glass slides were superhydrophilic (θS of water: less than 5°). Water droplets completely spread on these surfaces, so the dynamic water CAs and α could not be obtained. In contrast, the resulting θS values for Krytox- and [EMI][TFSI]-infused SNF-covered glass slides were markedly different (114° and 51°, respectively), but both surfaces showed small Δθ (3°) and α (4°) values, showing no marked differences in dynamic dewetting behaviors. This clearly indicates that both liquid film surfaces were very smooth, homogeneous, and immiscible with water. This led to good water sliding behaviors, independent of their absolute θS values. It was also confirmed that FAS17-coated SNF-covered glass slides showed superhydrophobicity (θS/θA/θR of 163°/167°/161°) and good water sliding properties, with small Δθ (6°) and α (3°) values.
We then investigated the anti-fogging properties of all of the samples in a cold/warm test. Both the superhydrophilic HST-[BHEDMA][MeSO3]-infused and the UV/ozone-cleaned SNF-covered glass slides remained fog-free (Figure 2E,F), but the other samples immediately fogged, as shown in Figure 2A–D. The former two surfaces were found to be effective for preventing water droplet formation. For UV/ozone-cleaned SNF-covered glass slides, condensed water fully spread across the sample surface, while water completely spread and/or was immediately absorbed into the HST-[BHEDMA][MeSO3]-infused surfaces. However, our IL-infused surfaces were unstable in bulk water. Unfortunately, the IL layer was easily removed from the sample surfaces when submerged in water.
These two samples also showed excellent anti-fogging properties against hot water vapor exposure. They remained fog-free, while the formation of tiny water droplets was observed on the other samples, resulting in significant increases in opacity (Figure S2). Several research groups have previously reported that hydrophobic LST liquid-infused and superhydrophobic surfaces have superior water-repellent abilities because condensed water droplets can easily slide off of such surfaces [49,50]. However, in our present case, in spite of having low CA hysteresis, the condensed water droplets could not be removed from these wet/dry (super)hydrophobic surfaces because the droplet sizes were too small to slide off. From these results, we concluded that water-immiscible liquid infused- and superhydrophobic surfaces were not suitable for anti-fogging applications.
When the anti-fogging tests were repeated several times, the condensed water gradually overflowed onto the [BHEDMA][MeSO3]-infused SNF-covered glass slide (Video S1), after the water absorption limit was reached. As a result, the infused [BHEDMA][MeSO3] flowed off simultaneously with the condensed water. However, such condensed water could be spontaneously removed by simply leaving samples for 21 min under low-humidity conditions at room temperature (at ≈20 °C and R.H. of ≈20%) (Figure 3A), because the water content of hygroscopic materials eventually reaches equilibrium with that of the atmosphere. In addition, because ILs are non-volatile liquids with high thermal stability, condensed water could be removed more quickly and repeatedly by simply heating at 100 °C for 3 min (Figure 3B and Figure S3). It should also be noted that since [BHEDMA][MeSO3] is hygroscopic, it always contains a certain amount of water, so exposure to a low-humidity environment or heating may cause the IL layer mass to decrease more than the amount of absorbed moisture (Figure 3A,B). It was also confirmed that even when the sample surface was scratched with a razor blade or tweezers several times, the voids were immediately refilled due to the IL’s excellent fluidity (self-healing, Video S2) [39], and the anti-fogging property remained unchanged. In this way, the [BHEDMA][MeSO3]-infused SNF-covered glass slide showed self-healing and reasonable reversible/repeatable anti-fogging properties.
Since only [BHEDMA][MeSO3]-infused and UV/ozone-cleaned SNF-covered glass slides were confirmed to be fog-free even after several anti-fogging tests, these samples were left in a laboratory environment, and their long-term anti-fogging properties were also investigated. Although the latter sample lost its anti-fogging properties in a week (Figure S4), its surface static wettability remained almost unchanged (θS value after 7 days still could not be measured, that is, nearly 0°). It is well known that superhydrophilic surfaces are easily contaminated by dust and impurities in air [36]. These impurities serve as nucleation sites of water droplet formation. In contrast, the [BHEDMA][MeSO3]-infused surface showed excellent anti-fogging performance even after 8 weeks (Figure S4), although airborne impurities were visible and clearly observed on the sample surface. These results suggested that the degradation of anti-fogging properties due to the adsorption of impurities was negligibly small for our HST-[BHEDMA][MeSO3]-infused surface compared to dry/rough surfaces. Since [BHEDMA][MeSO3] is non-volatile, superhydrophilic, and highly hygroscopic, it can absorb water, preventing the formation of water (micro)droplets on the IL surface. This is most likely the reason why our HST-IL-infused surface showed long-term anti-fogging properties.
It is well known that mixing water with molecules that contain a large number of polar groups (e.g., polyethylene glycol) effectively inhibits the formation of hydrogen bonding networks found in pure water, thereby lowering the freezing point of water [51]. This effect has been widely applied to anti-frosting applications [9,52,53]. We thus expected that our [BHEDMA][MeSO3]-infused surfaces also could show similar anti-frosting properties. To examine this, some of the samples were fixed to the Peltier cooler kept at −5 °C and left in air at ≈20 °C and an R.H. of 40−50%. As shown in Figure 4A,B, for bare and UV/ozone-cleaned SNF-covered glass slides, water condensed and frosted on these surfaces within 30 min. In contrast, frost formation on our [BHEDMA][MeSO3]-infused SNF-covered glass slide was found to be delayed and effectively prevented. No frost formation was observed within 60 min; however, after 3 h, frost formed on the surface (Figure 4C). This suggested that once [BHEDMA][MeSO3] was saturated with water, the condensation of water still continued to occur and eventually froze on the IL surface.

4. Conclusions

We successfully demonstrated for the first time the formation of a liquid-infused surface using a high-surface tension (HST) ionic liquid (IL) for anti-fogging applications. The liquid-infused surface was fabricated by infusing a non-volatile, HST (66.4 mN/m), and hygroscopic IL (bis(hydroxyethyl)dimethylammonium methanesulfonate ([BHEDMA][MeSO3]) into silica (SiO2) nano-frameworks (SNFs) formed on a glass slide. The resulting IL-infused SNF-covered glass slide was highly transparent, superhydrophilic, and showed excellent long-lasting anti-fogging (for more than 8 weeks) and reasonable anti-frosting properties, since the condensed water spread over and/or adsorbed onto the IL. While the infused IL could be removed from the surface with the increase in condensed water, this could be prevented by simply leaving the samples under low-humidity conditions at room temperature or by heating them to remove the adsorbed water. Therefore, the [BHEDMA][MeSO3]-infused surface was able to display reversible/repeatable anti-fogging properties. However, the lack of water stability in our IL-infused surfaces remains a critical issue for applying them as a practical anti-fogging coating. We expect that this problem can be solved to some extent by mixing with a gel matrix. The use of ILs with both high surface tension/hygroscopicity that exhibit high water stability [32] is another promising approach. Such experiments are ongoing. In terms of practical applications, long-lasting anti-fog/anti-frost properties are preferred. Thus, we believe that the use of non-volatile, superhydrophilic, and hygroscopic HST-ILs as an anti-fogging liquid is the key to realizing durable anti-fogging surfaces and could provide a basis for designing new styles of anti-fogging coatings/surfaces.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/surfaces7030031/s1, Figure S1: Typical SEM images of the SNFs deposited on a glass slide before and after the infusion of [BHEDMA][MeSO3]; Figure S2: Optical images of (A) bare glass slide, (B) [EMI][TFSI]- and (C) Krytox-infused SNF-covered glass slide, (D) FAS17-coated SNF-covered glass slide, (E) SNF-covered glass slide, and (F) [BHEDMA][MeSO3]-infused SNF-covered glass slide after hot vapor test; Figure S3: Changes in the mass of the IL layer for the [BHEDMA][MeSO3]-infused SNF-covered glass slide over 10 repeated cold/warm test heating cycles; Figure S4: Optical images of SNF-covered glass slides and [BHEDMA][MeSO3]-infused SNF-covered glass slide after cold/warm test; Video S1: Condensed water overflowing on the [BHEDMA][MeSO3]-infused SNF-covered glass slide; Video S2: Self-healing behavior of [BHEDMA][MeSO3]-infused SNF-covered glass slide during scratching with tweezers.

Author Contributions

Conceptualization, A.H.; methodology, A.H.; validation, A.H. and S.N.; formal analysis, S.N.; investigation, S.N. and S.S.; resources, A.H.; data curation, S.N.; writing—original draft preparation, A.H. and S.N.; writing—review and editing, J.W. and S.S.; visualization, S.N.; supervision, A.H.; project administration, A.H. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data will be made available on request.

Acknowledgments

The authors would like to thank Chihiro Urata and Tomoya Sato of AIST for their technical assistance.

Conflicts of Interest

The authors declare no conflicts of interest.

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Surfaces 07 00031 sch001
Scheme 1. Schematic illustration of preparation of HST-IL ([BHEDMA][MeSO3])-infused SNF-covered glass slide.
Scheme 1. Schematic illustration of preparation of HST-IL ([BHEDMA][MeSO3])-infused SNF-covered glass slide.
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Figure 1. (A) The appearances of SNF-covered glass slides (40 mm × 40 mm) before and after the infusion of [BHEDMA][MeSO3]. (B) The typical transmittance spectra of bare and SNF-covered glass slides before and after the infusion of [BHEDMA][MeSO3].
Figure 1. (A) The appearances of SNF-covered glass slides (40 mm × 40 mm) before and after the infusion of [BHEDMA][MeSO3]. (B) The typical transmittance spectra of bare and SNF-covered glass slides before and after the infusion of [BHEDMA][MeSO3].
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Figure 2. Typical optical images of (A) bare glass slide, (B) [EMI][TFSI]- and (C) Krytox-infused SNF-covered glass slide, (D) FAS17-coated SNF-covered glass slide, (E) SNF-covered glass slide, and (F) [BHEDMA][MeSO3]-infused SNF-covered glass slide after the cold/warm test.
Figure 2. Typical optical images of (A) bare glass slide, (B) [EMI][TFSI]- and (C) Krytox-infused SNF-covered glass slide, (D) FAS17-coated SNF-covered glass slide, (E) SNF-covered glass slide, and (F) [BHEDMA][MeSO3]-infused SNF-covered glass slide after the cold/warm test.
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Figure 3. Changes in the mass of the IL layer for the [BHEDMA][MeSO3]-infused SNF-covered glass slide before and after the anti-fogging test and after subsequent exposure to a low-humidity condition (at ≈20 °C and R.H. of ≈20%) (A) or heating at 100 °C for a certain amount of time (B). Single and double asterisks (* and **) indicate the mass of the IL layer before and after the anti-fogging test, respectively. The gray dotted line is the boundary line indicating that the IL layer mass is less than the original one.
Figure 3. Changes in the mass of the IL layer for the [BHEDMA][MeSO3]-infused SNF-covered glass slide before and after the anti-fogging test and after subsequent exposure to a low-humidity condition (at ≈20 °C and R.H. of ≈20%) (A) or heating at 100 °C for a certain amount of time (B). Single and double asterisks (* and **) indicate the mass of the IL layer before and after the anti-fogging test, respectively. The gray dotted line is the boundary line indicating that the IL layer mass is less than the original one.
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Figure 4. Snapshots of (A) bare glass slide, (B) SNF-covered glass slide, and (C) [BHEDMA][MeSO3]-infused SNF-covered glass slide fixed to Peltier cooler kept at −5 °C and left in air at ≈20 °C and R.H. of 40−50%.
Figure 4. Snapshots of (A) bare glass slide, (B) SNF-covered glass slide, and (C) [BHEDMA][MeSO3]-infused SNF-covered glass slide fixed to Peltier cooler kept at −5 °C and left in air at ≈20 °C and R.H. of 40−50%.
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Table 1. The static/dynamic water CAs (θS/θA/θR), CA hysteresis (Δθ), and substrate tilt angles (α) of the samples.
Table 1. The static/dynamic water CAs (θS/θA/θR), CA hysteresis (Δθ), and substrate tilt angles (α) of the samples.
SampleθS
(°)		θA/θR
(°/°)		Δθ
(°)		α
(°)
[BHEDMA][MeSO3]-infused SNF-covered glass slideN/AN/AN/AN/A
Bare glass slideN/AN/AN/AN/A
SNF-covered glass slideN/AN/AN/AN/A
[EMI][TFSI]-infused SNF-covered glass slide5151/4833
Krytox-infused SNF-covered glass slide114115/11234
FAS17-coated SNF-covered glass slide163167/16163
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Nakamura, S.; Wassgren, J.; Sugie, S.; Hozumi, A. Application of High-Surface Tension and Hygroscopic Ionic Liquid-Infused Nanostructured SiO2 Surfaces for Reversible/Repeatable Anti-Fogging Treatment. Surfaces 2024, 7, 482-492. https://doi.org/10.3390/surfaces7030031

AMA Style

Nakamura S, Wassgren J, Sugie S, Hozumi A. Application of High-Surface Tension and Hygroscopic Ionic Liquid-Infused Nanostructured SiO2 Surfaces for Reversible/Repeatable Anti-Fogging Treatment. Surfaces. 2024; 7(3):482-492. https://doi.org/10.3390/surfaces7030031

Chicago/Turabian Style

Nakamura, Satoshi, Jerred Wassgren, Sayaka Sugie, and Atsushi Hozumi. 2024. "Application of High-Surface Tension and Hygroscopic Ionic Liquid-Infused Nanostructured SiO2 Surfaces for Reversible/Repeatable Anti-Fogging Treatment" Surfaces 7, no. 3: 482-492. https://doi.org/10.3390/surfaces7030031

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