A robust nanometer-thick hydrophilic / oleophobic ionic liquid Anti-fog and self-cleaning coating

Abstract

A hydrophilic and oleophobic surface coating comprising an ionic liquid or a fluorinated ionic liquid. A method for applying a hydrophilic and oleophobic ionic liquid surface coating on a substrate, comprising creating an ionic liquid solution by dissolving the ionic liquid in a solvent; cleaning the substrate using an UV / Ozone cleaning device; submerging the cleaned substrate into the ionic liquid solution; pulling the substrate out of the ionic liquid solution.

Description

A ROBUST NANOMETER-THICK HYDROPHILIC / OLEOPHOBICIONIC LIQUID ANTI-FOG AND SELF- CLEANING COATINGRELATED APPLICATION

[0001] This application claims priority benefit under 35 U. S. C. § 119(e) of U. S. Provisional Application No.63 / 713,514 filed October 29, 2024, the contents of which are herein incorporated by reference.STATEMENT OF GOVERNMENT SUPPORT

[0002] This invention was made with government support under grant # 1904486 awarded by the National Science Foundation. The government has certain rights in the invention.FIELD OF THE DISCLOSURETechnical field

[0003] The present disclosure generally relates to the field of coatings and, more specifically, to ionic liquid coatings inclusive of long-lasting simultaneously hydrophilic and oleophobic nanometer-thick ionic liquid coatings.Background]0004] Surfaces more wettable to water than to oils are highly desired in a range of applications such as detergent- free cleaning, and anti-fogging coatings. Unfortunately, such surfaces are rare, typically consisting of fluoropolymer coatings with multi-step modification processes. Moreover, reported surfaces are often only mildly effective and will lose oleophobicity with time. The tunable nature of ionic liquids (ILs) makes them an attractive coating material, offering endless possibilities for customization and optimization.

[0005] The vast majority of solid surfaces, whether natural or manmade, are more oleophilic than they are hydrophilic; that is, they are more wettable to oils than to water1-4. However, surfaces with unique wettability properties differing from conventional ones, hold considerable appeal across various applications. While countless surfaces and coatings with specialized wettability have been identified or engineered, the demand persists for surfaces exhibiting greater affinity towards water than oils. Achieving simultaneous hydrophilic and oleophobic properties remains challenging primarily because lower surface tension liquidslike oils inherently exhibit better wetting on most surfaces compared to higher surface tension liquids such as water1-6. The scarcity of surfaces and coatings demonstrating this dual property results in a technological void, particularly in applications necessitating long-lasting antifogging coatings and detergent-free cleaning surfaces3,7'8. Another significant application lies in oil / water separation, where membranes with hydrophilic / oleophobic properties offer passive and highly selective water removal capabilities3,9'13.

[0006] Hutton et. al. were among the earliest to report hydrophilic / oleophobic surfaces, which they achieved using a cationic fluorosurfactant complexed with a weakly negatively charged plasma polymer surface and reported a water contact angle (WCA) below 20’ with a hexadecane contact angle at 82°3,14. They attributed this behavior to a reorganization of the coating monolayer which allowed water to interact with the hydrophilic surface below. Many of these surfaces have since relied on fluoropolymers such as polyethylene glycol with fluorinated end caps (f-PEG)15,16, polydicotylfluorine (PFO)17'19, perfluoropolyether (PFPE)1,2,6,20, or polyvinylidene fluoride (PVDF)21,22, as major components. These polymers are often modified with copolymeric substituents like poly(diallyldimethylammonium chloride)17,18,23,24or solid loadings including SiO217-19,25or CaSiO326nanoparticles. Other groups have focused specifically on hydrophilic / oleophobic membranes, which typically use a supporting material such as cellulose or steel mesh, and modifying the support surface with coatings like silanes or hydrogels9-’2>'8’27-29. For example, Xue et. al created a superhydrophilic and superoleophobic filter using polyacrylamide hydrogel on a stainless steel mesh, showing underwater contact angles over 150° for various oils and reached over 99% separation efficiency for oil / water mixtures12. Chi et. al coated a polyester fabric in a monomer solution of lH,lH,2H,2H-tridecafluoro-n-octyl acrylate, methacrylic acid, and polyethylene glycol diacrylate using a dipcoating procedure, followed by UV treatment to polymerize the coating material30. This copolymer coating also exhibited oil contact angles around 150° accompanied by impressive abrasion resistance that can likely be attributed to the covalent grafting.

[0007] A couple previous studies focused on perfluoropoly ethers (PFPE) Z-03, Zdol, and Ztetraol, which are single-component coatings, and investigated the effect of polar end groups1,2. Those results indicated that the degree of hydroxyl functionalization plays a crucial role in facilitating hydrogen bonding between PFPE andthe native oxide layer of an Si wafer surface. This interaction significantly enhances the coating's ability to selectively permit water penetration while repelling oil. They showed that in the absence of hydroxyl functionalization, the surface remained hydrophilic / oleophilic, suggesting that the polymer chains exhibited a disordered arrangement on the surface where both water and hexadecane molecules were able to permeate the coating with ease. For a PFPE with too many hydroxyl groups, two at each chain end, the surface became hydrophobic / oleophobic, indicating that the stronger hydrogen bonding created a significantly denser packing on the surface that neither liquid could penetrate. However, with a limited number of hydroxyl groups, the PFPE chains packed loosely enough to permit the passage of small water molecules, while insufficient space hindered the permeation of bulkier hexadecane molecules. This penetration mechanism was supported by time-dependent studies, where it was shown that the oleophobicity of Zdol degraded with oil exposure time1-3. It was explained that the observed initial Hexadecane Contact Angle (HCA) was not the thermodynamically equilibrated state, but rather, kinetically determined. The Zdol-coated surface consists of mobile polymer chains that relax (e.g. bend and twist) with time. As such, the initial contact angle alone does not necessarily represent the thermodynamic properties. In the case of water, the loose packing of Zdol allowed small water molecules to penetrate immediately on contact, explaining the low contact angle observed at the initial time. For hexadecane, the molecules are larger, so on initial contact, they rest on top of the PFPE coating. However, given sufficient time, the polymer chains can relax such that hexadecane is able to slowly penetrate the coating until it eventually interacts with the underlying surface. This degradation of the oleophobicity significantly limits the application of previous hydrophilic / oleophobic coatings.

[0008] Ionic liquids are promising candidates for further exploration of specially wettable surfaces. Their strong thermal and chemical stability, coupled with highly tunable molecular structures, has enabled their use in a wide range of applications over the past few decades31,32. For surface coatings, low surface tension is desirable to enable uniform wetting, which can be achieved through short fluorinated alkyl segments or short fluorinated segments.

[0009] To address shortcomings of the prior art, the present disclosure is directed to a functionalized ionic liquid coating with highly fluorinated alkyl segments and a polar end group comprising a preferablynanometer-thick coating promotes a high degree of oleophobicity on silica substrates due to the high fluorination, while maintaining a water contact angle (WCA) below 10°. Importantly, the oleophobicity is stable over at least 48 hours, indicating a robust simultaneous oleophobicity / hydrophilicity, which can be attributed to its inherently more rigid structure and limited relaxation. A preferred nanometer-thick coating of the present disclosure is effective for long-term antifogging and detergent- free cleaning. These results introduce new applications for functionalized ionic liquids and may open a new path for addressing the challenges of creating surfaces with special wettability.BRIEF SUMMARY OF THE DISCLOSURE

[0010] In a preferred aspect, the present disclosure comprises a hydrophilic and oleophobic surface coating comprising an ionic liquid.

[0011] In another preferred aspect of a hydrophilic and oleophobic surface coating of the present disclosure, the ionic liquid comprises a fluorinated ionic liquid.

[0012] In yet another preferred aspect of a hydrophilic and oleophobic surface coating of the present disclosure, the ionic liquid comprises 1-1H,1H,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazolium bis(nonafluorobutanesulfonyl)imide or 1-1H,1H,2H,2H-perfluorohexyl-3-methylimidazolium bis(nonafluorobutanesulfonyl)imide.]0013] In another preferred aspect of a hydrophilic and oleophobic surface coating of the present disclosure, the surface coating has a monolayer thickness.

[0014] In yet another preferred aspect of a hydrophilic and oleophobic surface coating of the present disclosure, the surface coating has a monolayer thickness of about 0.8 nm.

[0015] In an additional preferred aspect of a hydrophilic and oleophobic surface coating of the present disclosure, the surface coating has a thickness less than a monolayer thickness, or a thickness greater than a monolayer thickness, or a thickness from about 0.4 nm to about 5 nm.

[0016] In another preferred aspect of a hydrophilic and oleophobic surface coating of the present disclosure, the monolayer thickness is equal to about 0.8 nm.10017] In an additional preferred aspect, the present disclosure comprises a hydrophilic and oleophobic surface coating comprising an imidazolium-based ionic liquid with highly fluorinated alkyl segments.

[0018] In another preferred aspect of a hydrophilic and oleophobic surface coating of the present disclosure, the surface coating has a monolayer thickness.

[0019] In yet another preferred aspect of a hydrophilic and oleophobic surface coating of the present disclosure, the surface coating has a monolayer thickness of about 0.8 nm.

[0020] In another preferred aspect of a hydrophilic and oleophobic surface coating of the present disclosure, the surface coating has a thickness less than a monolayer thickness, or a thickness greater than a monolayer thickness, or a thickness from about 0.4 nm to about 5 nm.

[0021] In an additional preferred aspect of a hydrophilic and oleophobic surface coating of the present disclosure, the monolayer thickness is equal to about 0.8 nm.

[0022] In another preferred aspect, the present disclosure comprises a substrate having a hydrophilic and oleophobic surface coating, wherein the surface coating comprises an ionic liquid.

[0023] In another preferred aspect of a substrate having a hydrophilic and oleophobic surface coating of the present disclosure, the ionic liquid comprises a fluorinated ionic liquid.

[0024] In yet another preferred aspect of a substrate having a hydrophilic and oleophobic surface coating of the present disclosure, the ionic liquid comprises 1-1H,1H,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazolium bis(nonafluorobutanesulfonyl)imide or 1-1H,1H,2H,2H-perfluorohexyl-3-methylimidazolium bis(nonafluorobutanesulfonyl)imide.

[0025] In another preferred aspect of a substrate having a hydrophilic and oleophobic surface coating of the present disclosure, the substrate comprises silica, glass, plastic, ceramic, metal or metal oxide.

[0026] In another preferred aspect, the present disclosure comprises a method for applying a hydrophilic and oleophobic ionic liquid surface coating on a substrate, comprising creating an ionic liquid solution by dissolving the ionic liquid in a solvent; cleaning the substrate using an UV / Ozone cleaning device; submerging the cleaned substrate into the ionic liquid solution; pulling the substrate out of the ionic liquid solution.

[0027] In another preferred aspect of a method for applying a hydrophilic and oleophobic ionic liquid surface coating on a substrate of the present disclosure, the thickness of the ionic liquid surface coating on the substrate is controlled by varying the concentration of the ionic liquid in the ionic liquid solution.

[0028] In yet another preferred aspect of a method for applying a hydrophilic and oleophobic ionic liquid surface coating on a substrate of the present disclosure, the substrate is pulled out of the ionic liquid solution at a speed of about 0.1-10 mm / s.

[0029] In another preferred aspect of a method for applying a hydrophilic and oleophobic ionic liquid surface coating on a substrate of the present disclosure, the ionic liquid comprises a fluorinated ionic liquid with hydroxyl functionalization; 1-1H,1H,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazolium bis(nonafluorobutanesulfonyl)imide; or an imidazolium-based ionic liquid with highly fluorinated alkyl segments.BRIEF DESCRIPTION OF THE DRAWINGS

[0030] For the present disclosure to be easily understood and readily practiced, the present disclosure will now be described for purposes of illustration and not limitation in connection with the following figures, wherein:

[0031] FIG. 1(a) shows a comparison of deposited water and hexadecane drops on Si wafers before and after coating with ionic liquid. More specifically, FIG. 1(a) shows the initial WCA and initial HCA on two Si wafer substrates with ~1.4 nm thick HFILOH coatings compared to the bare wafers;

[0032] FIG. 1(b) is a chart showing the time-dependent HCA measurement on HFILOH-coated Si wafer compared to Zdol-coated wafer with early behavior (under 3 hr) is depicted on the left for visibility;

[0033] FIG. 1(c) is a chart showing Initial WCA (left) and HCA (right) of HFILOH coated Si wafers measured as a function of coating age, with each data point represents new drops of liquid on the aged sample;

[0034] FIG. 1(d) is a chart showing a comparison of time-dependent HCA for HFILOH coatings below, at, and above ML thickness of ~0.8nm;

[0035] FIG. 2(a) is a chart showing Same-drop HCA measurement on HFILOH-coated Si wafer compared to Zdol-coating with early behavior under 3 hours, and (b) long-term behavior up to 48 hours.

[0036] FIG. 2(b) is a chart showing Same-drop HCA measurement on HFILOH-coated Si wafer compared to Zdol-coating with long-term behavior up to 48 hours.

[0037] FIG. 3 presents charts showing that HCA on bare teflon substrate maintains a contact angle that is completely static for the duration of 48 hours;

[0038] FIG. 4 is a chart showing Time-dependent WCA on HFILOH / Si wafer wherein the contact angle remains relatively static for the measurable lifetime of the water drop;

[0039] FIG. 5 are charts showing ARXPS Cis and Nls spectra for HFILOH coatings at and above monolayer thickness. Cis peaks are color coded according to the molecular structure shown above. The bar charts compare the peak ratios between fluorinated carbons and each nitrogen at each coating thickness;

[0040] FIG. 6 shows glass slides that have been aged for 3 weeks of contamination before exposure to steam to promote fogging with the HFILOH-coated slide of the present disclosure (right) showing significantly improved visibility compared to the bare uncoated slide (left).

[0041] FIG. 7 shows self-cleaning of hexadecane from an uncoated glass slide (left) and a glass slide coated with a HFILOH coating of the present disclosure (right) glass slide after 3 weeks of ambient contamination;

[0042] FIG. 8 shows hexadecane and water contact angles on a silicon wafer with a 0.90nm HFILOH coating of the present disclosure before and after immersion in deionized water for 60 seconds;

[0043] FIG. 9 shows: F Is XPS spectra of HFILOH coatings on silicon wafers at normal (0°) and angled (45°). Spectra are shown for both monolayer and multilayer thicknesses;

[0044] FIG. 10 shows: AFM for monolayer (left) and multilayer (right) HFILOH coating of the present disclosure on Si wafer where Rq for monolayer is 0.146nm, and is 0.582nm for multilayer.DETAILED DESCRIPTION

[0045] In the following detailed description, reference is made to the accompanying examples and figures that form a part hereof, and in which is shown, by way of illustration, specific embodiments in which theinventive subject matter may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice them, and it is to be understood that other embodiments may be utilized and that structural or logical changes may be made without departing from the scope of the inventive subject mater. Such embodiments of the inventive subject matter may be referred to, individually and / or collectively, herein by the term "disclosure" merely for convenience and without intending to voluntarily limit the scope of this application to any single inventive concept if more than one is in fact disclosed.

[0046] The following description is, therefore, not to be taken in a limited sense, and the scope of the inventive subject matter is defined by the appended claims and their equivalents.

[0047] The present disclosure is directed to a nanometer-thick functionalized ionic liquid coating featuring highly fluorinated alkyl segments and polar end groups. This coating displays simultaneously hydrophilic and oleophobic behavior in air, with a water contact angle below 10° and a hexadecane contact angle of approximately 70° on silica substrates. Unlike most reported coatings that rely on polymeric architectures, micro-scale thicknesses, or underwater conditions, this behavior is achieved with a molecularly thin ionic liquid film applied via a single dipcoating step. Moreover, the oleophobicity remains stable for at least 48 hours of continuous exposure, suggesting resilient surface organization. Additionally, the antifogging and detergent- free cleaning capabilities of the coatings of the present disclosure have been qualitatively demonstrated, underscoring the potential thereof for multifunctional surface applications.Results and Discussion

[0048] According to the present disclosure, simultaneously hydrophilic and oleophobic behavior is demonstrated using a Highly Fluorinated Ionic Liquid with Hydroxyl functionalization (HFILOH), i.e. 1- 1 H, 1 H,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazolium bis(nonafluorobutanesulfonyl)imide, recently developed in our lab33, coating 10 on silicon wafers at nanometer-scale coating thicknesses. Prior research33has shown that the monolayer (ML) thickness of HFILOH is approximately 0.8nm based on the step change in surface roughness that can be seen using atomic force microscopy as well as simulated layering that was modeled using molecular dynamics. The surface of a clean silicon wafer is both highly hydrophilic and highly oleophilic, with very low contact angles <10°) for both water and hexadecane. FIG. 1(a) shows acomparison of deposited water and hexadecane drops on Si wafers before and after coating with ionic liquid. More specifically, FIG. 1(a) shows the initial WCA and initial HCA on two Si wafer substrates with ~1.4 nm thick HFILOH coatings compared to the bare wafers. After applying the HFILOH coating above monolayer thickness, the initial WCA remains low at 7.1° ± 1.2° while the HCA increases significantly to 72.4° ± 1.9°. FIG. 1(b) shows that on HFILOH-coated silicon wafers, the HCA only decreases by approximately 3° within the first two hours, then levels off gradually (i.e. only 2° more decrease) over the remainder of 48 hours, demonstrating that this oleophobicity is robust with time.10049] To observe the time-dependence of a single hexadecane drop on the HFILOH coating, the drop was deposited onto the substrate in a closed environment, limiting potential contamination due to ambient hydrocarbons in the air. FIG.2(a) shows that on HFILOH-coated silicon wafers, the HCA only decreases by approximately 3° within the first two hours, then in FIG.2(b), it levels off gradually (i.e. only 2° more decrease) over the remainder of 48 hours, demonstrating that this oleophobicity is resilient under constant exposure to oil. Comparatively, on a Zdol-coated wafer, the HCA begins at 69.8° ± 1.0° and decreases to 57.6° ± 3.6° in just the first two hours. By 48 hours, the HCA decreased to 49.2 ± 3.0° and the curve does not level off with time. The reductions in HCA with time are likely caused by a relaxation interaction between the hexadecane and the coating materials, as an ordinary solid surface such as polytetrafluoroethylene generally maintains a constant HCA with respect to time. (FIG. 3). The greater stability of HFILOH is likely due to its inherently more rigid structure compared to that of Zdol. The Zdol coating consists of flexible polymer chains that can more easily rearrange and allow hexadecane to penetrate with enough time. The smaller and more rigid cation and anion of HFILOH, however, allow very limited relaxation to occur early on, and the relaxation is largely inhibited thereafter. Time-dependent study of the WCA on HFILOH showed that over the measurable lifetime of a water drop, ~1 hour in a humid environment, the WCA held steady at 6.4° ± 1.4° (FIG. 4).

[0050] FIG. 1(d) compares the effect of coating thickness on HCA, which clearly shows that the thicker coatings display greater oleophobicity than thinner ones. Another interesting feature is the difference between the coatings above and below ML thickness for HFILOH. For the two thicknesses above ML, thecoating is very stable after the initial relaxation that occurs in the first two hours. However, the HCA on the thinner coating continues to decrease with time, similarly to Zdol. This may be caused by less uniform coverage by the coating below the ML, which could allow the hexadecane to interact with the Si wafer more easily with time than on a thicker coating.

[0051] The stability of the coating itself was also evaluated to ensure that the observed behaviors are not caused by aging of the sample. Here, rather than recording the contact angle of the same drop at different times, a new drop was applied to the same coated substrate at different locations and times, and the initial contact angle was recorded. As seen in FIG. 1(c), while there is noticeable variation in the initial WCA and HCA at each timestamp, the variation appears largely random and does not exhibit a clear positive or negative trend with time. This shows that the coating properties are stable, and suggests that the small decreases observed in the HCA for a single drop are due to a relaxation interaction with the hexadecane, rather than aging of the coating itself. Similar results are observed for the WCA, where the initial contact angles average 7.5° ± 2° over the first 48 hours after the substrate is coated with HFILOH.

[0052] To better understand the molecular orientation of the IL coating and its relationship with the wetting performance, the angle-resolved X-ray photoelectron spectroscopy (ARXPS) spectra of Cis and Nls for HFILOH coated silicon wafers have been collected and are shown in FIG. 5. Peak positions and areas can be found in Table 1 below. For the approximately ML thick coatings (0.88 ± 0.01nm), the ratio between the CF2 or CF3 peaks and either nitrogen peak increases significantly at a 45-degree incident angle compared to at 0°. As the 45-degree measurement is more surface sensitive, this suggests that the fluorinated carbon chains reside near the coating / air interface more preferentially than the cationic imidazole ring or the anionic sulfonimide group. The fluorinated segments positioned at the surface likely contribute largely to the observed oleophobicity. When the same measurement is taken on a thicker coating (1.32 ± 0.01nm), the ratios between the peaks at both angles are nearly the identical. This can be explained by a dewetting mechanism in which IL that is deposited beyond the monolayer thickness pulls itself into domains that resemble the bulk regime more than an ordered film34. However, the coating remains highly oleophobic and hydrophilic at these higher thicknesses because the fluorinated segments likely are still residing at the localsurfaces of the dewetted domains, just in a less uniformly-ordered arrangement when compared to the smooth monolayer coating.Table 1: Binding energies and peak areas for all assigned peaks in Cis and Nls XPS spectra of FIG. 5Table S2: Binding energies and peak areas for assigned peaks in FIs XPS spectra

[0053] A couple applications for this hydrophilic-oleophobic coating have been demonstrated as well. When glass or other lens materials become foggy, it is because water condenses on a hydrophobic surface, forming tiny beads that scatter light in various directions. Conversely, on a hydrophilic surface, water condenses as smooth sheets, resulting in less light scattering8. Although clean glass is naturally hydrophilic, it gradually becomes more hydrophobic over time due to hydrocarbon contamination coating its surface. The same can be said for antifogging coatings that are either superhydrophilic or superhydrophobic, as they are often susceptible to contamination by lower surface tension liquids8. FIG. 6 shows two initially clean glass slidesthat were exposed to ambient conditions for 3 weeks. The slide coated with an HFILOH coating 10 of the present disclosure exhibits only minor light distortions where there was excessive water buildup, compared to the uncoated slide that had reduced optical transmittance at all locations.[0054) Another notable application is in detergent-free cleaning surfaces. Given that most surfaces tend to be more readily wetted by oils than water, water alone struggles to effectively displace oils from a soiled surface. Traditional cleaning methods rely on the use of environmentally unfriendly surfactants, which interact with hydrocarbons to facilitate their removal by water. FIG. 7 depicts two slides that were exposed to ambient conditions for 3 weeks, followed by the deposition of several drops of dyed hexadecane. As the drops were applied to the uncoated slide, they immediately spread out and wetted large areas of the slide surface. In contrast, it was immediately observed that the slide coated with a HFILOH coating 10 of the present disclosure was still oleophobic as the drops maintained compact bead shapes that did not spread, despite having approximately the same liquid volumes. Subsequent immersion of each slide in water further demonstrated the coated slide was still more hydrophilic than it was oleophilic. Significant oil residue remained on the uncoated slide, which is expected for most ordinary surfaces without the use of a surfactant. Meanwhile, the HFILOH-coated slide appears completely clean, indicating that water alone was sufficient to displace the oil and wet the surface itself.

[0055] In addition to its demonstrated longevity, the HFILOH coating exhibits reusability following full immersion in water. Immersion allows maximum water penetration into the coating, which could potentially compromise performance if the liquid became trapped or dissolved the material. To assess this, a silicon wafer coated with a 0.90±0.02 nm HFILOH layer of the present disclosure was submerged in deionized water for 60 seconds and left to dry under ambient conditions for 50 minutes. After drying, the coating thickness decreased to 0.72±0.06 nm, indicating a partial loss of material. Contact angle measurements shown in FIG. 8 reveals a -12° decrease in HCA and ~6° increase in WCA relative to the as-prepared surface. While this reflects a modest reduction in performance, the coating clearly retains its hydrophilic / oleophobic behavior and is reusable without the need to reapplication or special treatment. Thehigh residual thickness after immersion suggests strong physical adhesion to the substrate, even in the absence of covalent bonding.

[0056] FIG. 9 shows: F Is XPS spectra of HFILOH coatings on silicon wafers at normal (0°) and angled (45°). Spectra are shown for both monolayer and multilayer thicknesses;

[0057] Atomic Force Microscopy. The surface topography of the nanometer-thick ionic coating on Si wafer is evaluated by AFM using a Bruker Dimension Icon Atomic Force Microscope as shown in FIG. 10. FIG.10 shows: AFM for monolayer (left) and multilayer (right) HFILOH coating of the present disclosure on Si wafer where Rq for monolayer is 0.146nm, and is 0.582nm for multilayer. The AFM probe is MikroMasch NSC14 / AL BS with a resonance frequency of 160 kHz, a force constant of 5.0 N / m, and an 8 nm aluminum tip. The scans are conducted in tapping mode with an image acquisition of 512 x 512 pixels. The lateral resolution of the scans is 20 nm as the scan area is 10 x 10 pm2, and the vertical resolution is ~0.1 nm Conclusion

[0058] In conclusion, highly hydrophilic and oleophobic surfaces were successfully created using a nanometer-thick coating imidazolium-based ionic liquid with highly fluorinated alkyl segments and hydroxyl functionalization. A facile dip-coating procedure produced nanometer-thick coatings using minimal material while achieving effective and stable hydrophilicity / oleophobicity. Time-dependent experiments showed that after the HCA initially reduced by couple degrees on the HFILOH-covered surface, oleophobicity was strongly maintained over a long period of continuous exposure. This highly stable simultaneous oleophobicity / hydrophilicity can be attributed to its inherently more rigid structure and limited relaxation. The finding was further reinforced by the contamination tests in which the coated glass slides retained hy drophili c / oleophobic behavior even after three weeks of ambient exposure. Total immersion of the coated silicon wafer in water demonstrated reusable performance, though additional immersion cycles and abrasion resistance experiments are needed to further validate its suitability for practical application. While XPS results suggest that the molecular arrangement favors fluorinated segments at the surface-air interface, further investigation into the underlying mechanism and optimization of these coatings could lead to the widespread use of ionic liquids in a variety of applications that require surfaces with controlled wettability.

[0059] According to the present disclosure, highly hydrophilic and oleophobic surfaces were successfully created using a nanometer-thick imidazolium-based ionic liquid with highly fluorinated alkyl segments and hydroxyl functionalization. A facile dip-coating procedure produced nanometer-thick coatings using minimal material while achieving effective and stable special wettability. Time-dependent experiments showed that after hexadecane initially relaxed on the HFILOH-covered surface, reducing the HCA by only a couple degrees, oleophobicity is strongly maintained over a long period of continuous exposure. This highly robust simultaneous oleophobicity / hydrophilicity can be attributed to its inherently more rigid structure and limited relaxation. Preferably, the nanometer -thick imidazolium-based ionic liquid with highly fluorinated alkyl segments and hydroxyl functionalization coating of the present disclosure is oil-resistant, contaminants-resistant, anti-friction and anti-wear. It has been demonstrated according to the present disclosure that the nanometer-thick coating is effective for long-term antifogging and detergent-free cleaning.

[0060] Experimental

[0061] Preparation of Samples: The synthesis of HFILOH has been described previously33. The IL nanofilms are applied to the Si wafer surface via a dip-coating procedure previously established in our lab33. The HFIL-OH is dissolved in Vertrel XF to prepare dilute solutions. The Si wafers undergo 30-minutes of UV / Ozone treatment using a BioForce Nanosciences UV / Ozone Procleaner (Power specifications: 110V AC, 50 / 60 HZ, 0.5A, and 1 PH) with 185 and 254 nm wavelengths in ambient air at room temperature. The wafer is vertically submerged into and subsequently pulled out from the dilute solutions at a speed of 1 mm / s using a KSV Instrument dipcoater. The thickness of the lubricant films is directly controlled by changing the solution concentration.

[0062] The IL nanofilms are applied to the Si wafer surface via a dip-coating procedure previously established in our lab. The HFIL-OH is dissolved in Vertrel XF to prepare dilute solutions. The Si wafers undergo 30-minutes of UV / Ozone treatment using a BioForce Nanosciences UV / Ozone Procleaner (Power specifications: 110V AC, 50 / 60 HZ, 0.5A, and 1 PH) with 185 and 254 nm wavelengths in ambient air at room temperature. The wafer is vertically submerged into and subsequently pulled out from the dilutesolutions at a speed of 1 mm / s using a KSV Instrument dipcoater. The thickness of the lubricant films is directly controlled by changing the solution concentration.

[0063] Thicknesses of the fabricated IL nanofilms are measured using a J. A. Woollam alpha-SE Spectroscopic Ellipsometer at an incident angle of 75° and a beam diameter of ~2 mm. Optical constants of the native oxide surface are determined using "NTVE_JAW" database complex refractive index after UV / Ozone treatment and before dip coating. After dip-coating, the Cauchy dispersion model is used to measure the thickness of the IL nanofilms. The measured thicknesses are the average thicknesses within the beam spot.

[0064] Contact Angles The HCA and WCA of nanometer-thick lubricants on the substrates are measured using a VCA Optima Contact Angle system. 0.5 pL drops of testing liquids are automatically dispensed on the surfaces, and the drop shapes are captured using a CCD camera and analyzed using the vendor-supplied software. The reported contact angles are averages from individual drops deposited on at least three separate substrates with similar film thicknesses (within 0.15nm). Sample substrates are confined in an acrylic container sealed with parafilm to minimize ambient hydrocarbon contamination for the duration of each experiment.

[0065] X-Ray Photoelectron Spectroscopy: Monolayer and multilayer film were analyzed using a ThermoFisher EscaLab 250Xi photoelectron spectrophotometer. Monochromatic Al Kα X-ray was used as the source of the incident radiation. The pressure of the analysis chamber was 2x1 O’9mBar. Pass energy was 150 eV for survey spectra and 20 eV for fine spectra of Nls and Cis. Dwell time was 50 msec for survey spectra and 100 ms for fine spectra of Nls, FIs and Cis. Step length was 0.1 eV for survey spectra and 0.07 eV for fine spectra. The measurements were taken at 0° and 45° for both monolayer and multilayer film. CasaXPS was used to fit the peaks. Shirley background was used and Gaussian Lorentzian 50% was used to fit the curve. The aliphatic carbon peak was set to 284.6 eV and the binding energies were corrected.

[0066] Anti-fogging'. Glass slides are taken as-is from the packaging and are dip-coated according to the aforementioned procedure. The coated slides are then laid out on the benchtop beside uncoated “control” slides and both sets are exposed to the ambient environment. After three weeks, slides from each set are held1 inch above boiling water for 10 seconds each to allow sufficient condensation to form. The slides are then immediately held 1 inch above a self-written sample text to qualitatively observe distortion.

[0067] Detergent-Free Cleaning: Glass slides are taken as-is from the packaging and are dip-coated according to the aforementioned procedure. The coated slides are then laid out on the benchtop beside uncoated “control” slides and both sets are exposed to the ambient environment. After three weeks, several drops of red-dyed hexadecane are deposited on the surface of slides from each set. The slides are then immediately hand-dipped twice into clean DI water before collecting images.References

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[0103] In the foregoing Detailed Description, various features are grouped together in a single embodiment to streamline the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments of the disclosure require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment.

Claims

What is claimed is:

1. A hydrophilic and oleophobic surface coating comprising an ionic liquid.

2. The surface coating of claim 1, wherein the ionic liquid comprises a fluorinated ionic liquid.

3. The surface coating of claim 1, wherein the ionic liquid comprises 1-1H,1H,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazolium bis(nonafluorobutanesulfonyl)imide or 1 -1H, 1 H,2H,2H-perfluorohexyl-3-methylimidazolium bis(nonafluorobutanesulfonyl)imide.

4. The surface coating of claim 1, wherein the surface coating has a monolayer thickness.

5. The surface coating of claim 1, wherein the surface coating has a monolayer thickness of about 0.8 nm.

6. The surface coating of claim 1, wherein the surface coating has a thickness less than a monolayer thickness, or a thickness greater than a monolayer thickness, or a thickness from about 0.4 nm to about 5 nm.

7. The surface coating of claim 6, wherein the monolayer thickness is equal to about 0.8 nm.

8. A hydrophilic and oleophobic surface coating comprising an imidazolium-based ionic liquid with highly fluorinated alkyl segments.

9. The surface coating of claim 8, wherein the surface coating has a monolayer thickness.

10. The surface coating of claim 8, wherein the surface coating has a monolayer thickness of about 0.8 nm.

11. The surface coating of claim 8, wherein the surface coating has a thickness less than a monolayer thickness, or a thickness greater than a monolayer thickness, or a thickness from about 0.4 nm to about 5 nm.

12. The surface coating of claim 11, wherein the monolayer thickness is equal to about 0.8 nm.

13. A substrate having a hydrophilic and oleophobic surface coating, wherein the surface coating comprises an ionic liquid.

14. The substrate of claim 13, wherein the ionic liquid comprises a fluorinated ionic liquid.

15. The substrate of claim 13, wherein the ionic liquid comprises l-lH,lH,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazolium bis(nonafluorobutanesulfonyl)imide or l-lH,lH,2H,2H-perfluorohexyl-3-methylimidazoliumbis(nonafluorobutanesulfonyl)imide.

16. The substrate of claim 13, wherein the substrate comprises silica, glass, plastic, ceramic, metal or metal oxide.

17. A method for applying a hydrophilic and oleophobic ionic liquid surface coating on a substrate, comprising:creating an ionic liquid solution by dissolving the ionic liquid in a solvent;cleaning the substrate using an UV / Ozone cleaning device;submerging the cleaned substrate into the ionic liquid solution;pulling the substrate out of the ionic liquid solution.

18. The method of claim 17, wherein the thickness of the ionic liquid surface coating on the substrate is controlled by varying the concentration of the ionic liquid in the ionic liquid solution.

19. The method of claim 17, wherein the substrate is pulled out of the ionic liquid solution at a speed of about 0.1-10 mm / s.

20. The method of claim 17, wherein the ionic liquid comprises a fluorinated ionic liquid with hydroxyl functionalization; l-lH,lH,2H,2H-perfluorohexyl-3-2-hydroxylethylimidazolium bis(nonafluorobutanesulfonyl)imide; or an imidazolium-based ionic liquid with highly fluorinated alkyl segments.

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