Slips surface coatings

Abstract

The present disclosure relates to surface coatings comprising a reticulated structure that is a metal-organic framework having pores or a covalent organic framework having pores, and a lubricant comprising lubricant molecules, wherein the lubricant molecules are held within the pores of the reticulated structure and extend from the pore apertures thereof. Also disclosed are methods of making such coatings, surfaces comprising such coatings, and kits comprising the reticulated structure and the lubricant.

Description

[0001] SLIPS SURFACE COATINGS

[0002] The project leading to this application has received funding from the European Union’s Horizon 2020 Research and Innovation programme under grant 801229 (HARMoNIC) and European Research Council (ERC) grant 714712 (NICEDROPS), and the ERC Consolidator Grant (selected by ERC and funded by UKRI, EP / X023974 / 1).

[0003] Field of the Invention

[0004] The present invention relates to a surface coating comprising a reticulated structure having pores and a lubricant (commonly referred to as a SLIPS coating), and particularly, although not exclusively, to the case where the reticulated structure is a metal-organic framework. The present invention also relates to substrates comprising such surface coatings; to methods of preparing such substrates; and to kits comprising such reticulated structures and lubricants.

[0005] Background

[0006] Nepenthes pitcher plant inspired slippery lubricant infused porous surfaces (SLIPS) have been widely researched due to their tremendous potential in solving real-life problems such as undesirable ice formation on surfaces, fouling, biofouling and drag in water treatment systems and on underwater vehicles1-4. SLIPS present a smooth, defect-free interface and can be designed to repel all immiscible liquids5-7, with minimal wetting hysteresis. However, with use the lubricant depletes from the surface over time, leading to failure of its slippery behaviour8-10. Strategies such as holding oil inside a polymer film or using capillary forces from surface nanopores have only had limited success. Use of solid and / or highly viscous liquid lubricants offers application-specific improvements but overall, durability challenges remain unsolved11 12.

[0007] For example, efforts have been made to identify suitable combinations of (hierarchical) textures, materials and lubricants; to achieve lubricant replenishment through surface energy gradients, external stimuli and use of reservoirs; and to entrap the lubricant in small surface pores via capillary forces and covalent immobilisation. These strategies mostly involved fluorinated compounds and resulted in only modest improvements3 13-17. Another common issue is cloaking (coverage) of droplets by a film of lubricant due to strong interactions between the lubricant (e.g., oil) and the liquid droplet. Recently, viscous lubricants were shown to minimise cloaking of droplets of ethanol (a low surface tension liquid)12. The strategy does not work for water droplets and the high viscosity lubricants also lower the droplet mobility (inversely proportional to the oil viscosity)10. Solid and / or highly viscous liquid lubricants show prolonged usability for anti-icing and condensation applications11 12. However, such surfaces remain susceptible to high-speed liquid impacts. Clearly, a better and rational strategy to ‘hold’ low viscosity oils on the surface for optimal drop mobility and improved impact resistance is desirable. Indeed, SLIPS that resist the impact forces anywhere near even those from high-speed rain-drops (~10 m / s), for example, remain unachieved. Rain 008864365

[0008] 2 drops impinging on transport vehicles in harsh-weather conditions can readily reach impact speeds >10 m / s and thus present a major challenge.

[0009] Holding lubricants using capillary pressure818, cross-linking19, physical20and covalent bonding1721have only resulted in minor improvements in SLIPS durability. For example, Laney et al. used nanoscale surface texture to increase the depletion time18and a couple of studies have used NH2-UiO-66 metalorganic frameworks (MOFs) infused with silicone oils to prepare SLIPS with anti-icing capabilities17 22. However, the improvements were limited due either to a lack of adequately fine surface texture or to the use of MOFs without a rational consideration for the pore size and chemistry. The surface slipperiness - marked by ready slippage of droplets on them at <10° surface inclination - was lost in <2 hr under continuous water dripping (shedding), or the ice-adhesion strength increased (>20 kPa) just after 10 icing / de-icing cycles. It is clear that a random design is most likely to fail. In an another example, silane functionalised UiO-66 MOFs infused with silicone oil with a viscosity of 500 cSt (designated as Si500 henceforth) failed in less than 30 minutes of water shedding (i.e. steady dripping of droplets and allowing them to slide past the surfaces)23. Crucially, none of these works considered liquid impact at high speed17 22.

[0010] The present invention has been devised in light of the above considerations.

[0011] Summary of the Invention

[0012] In a first aspect, the present invention relates to a surface coating comprising a reticulated structure that is a metal-organic framework having pores or a covalent organic framework having pores, and a lubricant comprising lubricant molecules, wherein the lubricant molecules are held within pores of the reticulated structure and extend from the pore apertures thereof.

[0013] In some embodiments the section of the lubricant molecules held within the pores of the reticulated structure have a maximum chain diameter that is no less than 10% of the diameter of the pore apertures.

[0014] Herein, “reticular”, “reticulation” and “reticulated” are given their normal meanings in the art. A reticular structure is an extended, crystalline structure formed through the linking of smaller chemical moieties by either coordination or covalent bonds. The reticular structures of the present invention are metal-organic frameworks (MOF) or covalent organic frameworks (COF), both of which have pores. The pores of the reticulated structure are contained within the reticulated structure itself, i.e. within the MOF or COF itself. It is understood that the pores of the reticulated structure do not refer to spaces between separate particles or layers of reticulated structure, or spaces formed by defects.

[0015] The surface coatings include a lubricant. The term “lubricant” is common-place in the field of slippery liquid-infused porous surfaces (SLIPS). Herein lubricants comprise lubricant molecules. In some cases, the lubricants consist of lubricant molecules. The lubricant molecules are held and retained within the reticulated structure and specifically within the pores of the reticulated structure. The retention of the lubricant molecules creates a supramolecular lubricant structure throughout the reticulated structure. 008864365

[0016] 3

[0017] Holding of the lubricant molecules is achieved by control or selection of the relative sizes of the pore apertures in the reticulated structure and the chain diameter of the lubricant molecules. The lubricant molecules have a section that has a chain diameter that is smaller than the pore aperture, allowing for insertion into the pores of the reticulated structure, and for strong guest-host interaction. The lubricant molecules are held within the pores of the reticulated structure, but also extend therefrom, which is essential for the functioning of the surface coating - the lubricant molecules must be exposed on the outer surface of the reticulated structure in order to create or contribute to the low friction (i.e. slippery) properties of the surface coating. Put another way, there is a section of the lubricant molecule that is held within the pore of the reticulated structure (i.e. extends inwards from the aperture of the same pore), and a section immediately adjacent to that section which extends outwards from the aperture of the same pore.

[0018] It may be that the lubricant fills substantially all of the pore in which it is held and inserted into, for example substantially fills the length of the pore. It may be that the lubricant molecules entirely fill the pores in which they are held and inserted into, for example entirely fill the length of the pores. It may be that the lubricant molecules fill > 50%, > 60%, > 70%, > 80%, > 90% or > 95% of each pore in which they are held. It may be that the lubricant fills > 50%, > 60%, > 70%, > 80%, > 90% or > 95% of the total number of pores of the reticulated structure. It may be that the lubricant fills > 50%, > 60%, > 70%, > 80%, > 90% or > 95% of the total pore volume of the reticulated structure. Filling of the pores of the reticulated structure can be observed, for example, using BET-surface area measurements. In such a case, it may be that the BET-surface area of the reticulated structure after infusion with lubricant is reduced by > 50%, > 60%, > 70%, > 80%, > 90%, > 95%, > 96%, > 97% or > 98% relative to the BET- surface area of the reticulated structure before infusion with lubricant.

[0019] Significant, substantially complete, or complete insertion and filling of the pores of the reticulated structure is only possible due to the chain diameter of the lubricant molecule being a certain amount smaller than the pore aperture diameter. It may be that the pores of the reticulated structure into which the lubricant molecules are inserted are aligned pores, in that they are arranged anisotropically through the reticulated structure, for example the axis of the pores are aligned in at least one direction through the reticulated structure.

[0020] It may be that the section of lubricant molecule that is held within the pores of the reticulated structure has a chain diameter that is no less than 10%, no less than 20%, no less than 30%, no less than 40%, no less than 50%, no less than 60%, no less than 70%, no less than 80% or no less than 90% of the diameter of the aperture of the pore in which it is held. It may be that the section of lubricant molecule that is held within the pores of the reticulated structure has a chain diameter that is no more than 0.5 A smaller than the diameter of the aperture of the pore it is held within, in some cases, no more than 1 .0 A, no more than 1 .5 A, no more than 2 A, no more than 2.5 A, no more than 3 A, no more than 3.5 A, no more than 4 A, no more than 4.5 A, or no more than 5 A smaller than the diameter of the aperture of the pore it is held within. The matching of size and geometry between reticulated structure pore apertures and lubricant molecule chain diameter maintains strong guest-host interaction, and reduces the ease in which the 008864365

[0021] 4 lubricant can be removed from the reticulated structure. In turn, this creates a more robust SLIPS surface, which retains low friction surface properties for longer, and even when subjected to extreme conditions (e.g. resistance to more extreme conditions compared to a material in which the pore apertures and lubricant molecular chain diameter are less well matched).

[0022] It may be that the pore aperture of the reticulated structure has a diameter that is from 1 to 20 angstroms (A), from 1 to 18 A, from 2 to 15 A, from 2 to 12 A, from 3 to 10 A, or from 4 to 8 A. It may be that the pore aperture has a diameter that is about 1 , about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, about 10, about 11 , about 12, about 13, about 14, about 15, about 16, about 17, about 18, about 19 or about 20 A, or falls within a range made from any combination of the foregoing (for example, from 13 to 17 A). It is understood that, depending on the shape of the pore aperture, diameter may be referring to the smallest distance across the centre of an aperture, or the average distance across the centre of an aperture. The pore aperture is understood to be the space or window providing access to the pore interior, that is the aperture through which the lubricant molecule is inserted, to be held within the reticulated structure. Pore aperture diameters can be measured by scanning tunnelling microscopy, by high resolution transmission electron microscopy, or by DFT calculations using the confirmed crystal structure from XRD experiments.

[0023] It may be that the lubricant molecule chain diameter is from 1 to 19 A, from 1 to 18 A, from 2 to 15 A, from 2 to 12 A, from 3 to 10 A, from 4 to 8 A, or from 4 to 7 A. It may be that the lubricant molecule chain diameter is about 1 , about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, about 10, about 11 , about 12, about 13, about 14, about 15, about 16, about 17, about 18, or about 19 A, or falls within a range made from any combination of the foregoing (for example, from 13 to 17 A). The lubricant molecule chain diameter, for example in a given section, is calculated as the sum of branch bond lengths, which herein are calculated after structure optimization using quantum method PM7. For example, for silicone oil the lubricant chain diameter is the arithmetic sum of bond lengths between the centre of atoms in the chain H-C-Si-C-H. It is understood that the bond lengths used should correspond to the part of a chain, or a section of chain, with the largest diameter.

[0024] The lubricant molecules extend from the pore apertures of the reticulated structure pores in which they are held, and in this way are not completely contained within the pores of the reticulated structure. The extension of the lubricant molecule in this way from the reticulated structure is important to ensure good performance of the surface coating. It may be that > 10%, > 20%, > 30 %, > 40%, > 50%, > 60%, > 70%, > 80%, or > 90% of the lubricant molecule chain length extends from the pore aperture. It may be that the lubricant molecule chain is > 2, > 3, > 4, > 5, > 6, > 7, > 8, > 9, > 10, > 20, > 50, > 100, or > 1000 times longer than the corresponding pore in which a section of the molecular chain is held.

[0025] The lubricant comprises long chain molecules. It may be that the long chain molecules are linear or branched, so long as they are still capable of being held within the pores of the reticulated structure. It may be that the lubricant comprises molecules with a substantially uniform chain diameter. The long chain molecules may be lipophilic or hydrophobic. It may be that the long chain molecules are 008864365

[0026] 5 hydrophobic. It may be that the lubricant is selected from the group consisting of silicone oil (for example, silicone 50, silicone 500 or silicone 1000), and fluorinated molecules (for example, fomblin® and krytox®).

[0027] The surface coatings of the present invention exhibit impressive and durable low-friction properties. These can be seen through, for example, in anti-icing performance. It may be that the surface coatings of the present invention exhibit an ice adhesion strength of < 20 kPa, < 15 kPa, < 10 kPa, or < 5 kPa (as measured by, for example, the methods described herein). It may be that such low ice adhesion strengths are maintained even following multiple icing / de-icing cycles, for examples after 10, 20, 30, 40 or 50 icing / de-icing cycles.

[0028] Low-friction properties are maintained even after exposure of the surface coating to shear forces. It may be that the surface coatings of the present invention are able to resist fluid impact and retain low-friction properties, for example the above ice-adhesion strengths, when impacted by fluid where the Weber number of the impact stream is > 2,500, > 5,000, > 10,000, > 15,000, > 20,000, > 25,000, > 30,000, > 35,000, or > 40,000.

[0029] The surface coatings of the present invention are capable of exhibiting amphiphobicity, hydrophobicity or lipophobicity, depending on how they are formulated. “Amphiphobicity” is the ability to display both hydrophobic and oleophobic properties. It may be that amphiphobic surface coatings of the present invention repel both aqueous liquids and low surface tension solvents. Low surface tension solvents include, for example butanone, ethanol, methanol, acetone, 1-butanol, 1-decanol, glycol, cyclohexanol and 1 ,2-butanediol, and vegetable oil.

[0030] Hydrophobicity and hydrophilicity may be assessed by measuring water drop contact angle. For example, it may be that a hydrophobic surface has a water drop contact angle of > 90°, > 95°, > 100°, > 105°, or > 110°. For example, it may be that a hydrophilic surface has a water drop contact angle of < 90°, < 85°, < 80°, < 75°, or < 70°. The water drop contact angle hysteresis is a measure of slipperiness of the surface coating, and is calculated from the advancing (0Adv) and receding (0Rec) contact angles of a water drop, for example using computer software and video recordings in ways which are well known to the skilled reader. It may be that the contact angle hysteresis of the present coatings is < 15°, < 12.5°, < 10°, < 7.5°, or < 5°. The slipperiness of the surface coatings may also be characterized by inclination angle that causes slippage. It may be that the inclination angle to cause water droplet slippage for the present coatings is < 20°, < 15°, < 10°, or < 5°.

[0031] In some embodiments, the reticulated structure comprises a functional group that is complementary to the lubricant molecules.

[0032] In some embodiments, the functional group of the reticulated structure is aprotic.

[0033] In some embodiments, the lubricant molecules comprise a functional group that is complementary to the reticulated structure.

[0034] In some embodiments, the functional group of the lubricant molecules is aprotic. 008864365

[0035] 6

[0036] It may be that the reticulated structure comprises a functional group that is complementary to, and interacts with, a functional group on the lubricant molecules.

[0037] The reticulated structure may comprise a functional group that is complementary to the lubricant molecules. It may be that this functional group is a post-synthetic functionalisation or modification, that is added to the reticulated structure after it has been formed. For example, in the case of the reticulated structure being a MOF, it may be that the MOF is prepared, and the functional group is added to a reactive group of a linker therein. It may be that the functional group of the reticulated structure stabilises the lubricant molecules in the pores of the reticulated structure, holding and retaining the lubricant molecules in the pores. It may be that the functional group of the reticulated structure and the lubricant molecules form chemical or physiochemical bonds with one another. It may be that such bonds are stronger than the bonds created between lubricant molecules and reticulated structure in the absence of the functional group of the reticulated structure. For example, the complementary nature of the functional group of the reticulated structure and the lubricant molecules may result in one or more of dipole-dipole interactions, the Debye force and Van der Waals interactions which act to hold the lubricant molecules within the pores of the reticulated structure.

[0038] The lubricant molecules may comprise a functional group. It may be that the functional group of the lubricant molecules is a post-synthetic functionalisation or modification, that is added to the lubricant molecular structure after it has been formed, or acquired. For example, the functional group of the lubricant molecules may be directly bonded to the main chain or backbone of the lubricant molecule, or may be indirectly bonded to the main chain or backbone. It may be that the functional group of the lubricant molecules stabilises the lubricant molecules in the pores of the reticulated structure, holding and retaining the lubricant molecules in the pores. It may be that the functional group of the lubricant molecules and the reticulated structure form chemical or physiochemical bonds with one another. It may be that such bonds are stronger than the bonds created between lubricant molecules and reticulated structure in the absence of the functional group of the lubricant molecules. For example, the complementary nature of the functional group of the lubricant molecules and the reticulated structure may result in one or more of dipole-dipole interactions, the Debye force and Van der Waals interactions which act to hold the lubricant molecules within the pores of the reticulated structure

[0039] The functional groups of the reticulated structure and lubricant molecules are chemical moieties that are added to the reticulated structure or the lubricant molecules to introduce specific functionality and to alter the “base” reticulated structure or lubricant molecules.

[0040] It may be that both a functional group on the reticulated structure and a functional group on the lubricant molecules are present in the surface coating of the present invention. The functional group of the reticulated structure and the functional group of the lubricant molecules in such a case are complementary and stabilise, possibly to a greater extent than when only including one of the functional groups on either the reticulated structure or lubricant molecules, the lubricant molecules in the pores of the reticulated structure, holding and retaining the lubricant molecules in the pores. It may be that the functional groups on the reticulated structure and the lubricant molecules form chemical or 008864365

[0041] 1 physiochemical bonds with one another. For example, the complementary nature of the functional groups on the reticulated structure and the lubricant molecules may result in one or more of dipole-dipole interactions, the Debye force and Van der Waals interactions which act to hold the lubricant molecules within the pores of the reticulated structure. The functional group on the reticulated structure and the functional group on the lubricant molecules may be the same or different.

[0042] It may be that the functional group of the reticulated structure is an aprotic group. Independently, it may be that the functional group of the lubricant molecules is an aprotic group. If both present, it may be that both the functional group of the reticulated structure and the functional group of the lubricant molecules are aprotic groups.

[0043] Examples of aprotic groups include halogen atoms, halogen containing groups (e.g. haloalkyl), alkyl groups, alkenyl groups, alkynyl groups, alkoxy, aminoalkyl, aryl, aralkyl and heteroaryl groups. It may be that the functional group of the reticulated structure is or comprises alkyl, ethyl, propyl and butyl. It may be that the functional group of the reticulated structure is or comprises a fluorine, chlorine or bromine. It may be that the functional group of the lubricant molecules is or comprises alkyl, ethyl, propyl and butyl. It may be that the functional group of the lubricant molecules is or comprises a fluorine, chlorine or bromine. If both present, it may be that both of the functional groups of the reticulated structure and lubricant molecules independently are or comprise fluorine, chlorine or bromine. If both present, it may be that both of the functional groups of the reticulated structure and lubricant molecules independently are or comprise methyl, ethyl, propyl or butyl.

[0044] It may be that the functional group of the reticulated structure is a substantially non-polar or weakly polar group. Independently, it may be that the functional group of the lubricant molecules is a substantially non-polar, or weakly polar group. If both present, it may be that both of the functional groups of the reticulated structure and the lubricant molecules are non-polar or weakly polar groups.

[0045] It may be that the functional group of the reticulated structure is a polar group. Independently, it may be that the functional group of the lubricant molecules is a polar group. If both present, it may be that both of the functional groups of the reticulated structure or the lubricant molecules are polar groups.

[0046] It may be that the functional group of the reticulated structure is a protic group. Independently, it may be that the functional group of the lubricant molecules is a protic group. If both present, it may be that both of the functional groups of the reticulated structure and the lubricant molecules are protic groups. Examples of protic groups include hydroxyl, alkyl hydroxyl, amine, and alkyl amine.

[0047] If both present, the functional group of the reticulated structure and the functional group of the lubricant molecules may be complementary and may be formed from any complementary combination of the aprotic, weakly polar, polar, or protic groups described above. For example, the functional group of the reticulated structure may be alkyl, and the functional group of the lubricant molecules may be fluorine. It may be that reticulated structure comprises no protic groups. It may be that the lubricant molecules comprise no protic groups. 008864365

[0048] 8

[0049] When both present, the complementary nature of the functional group of the reticulated structure and the functional group of the lubricant molecules, act together to hold the lubricant molecules within the pores of the reticulated structure more strongly to increase the robustness of the surface coating, and the longevity of the low-friction properties it exhibits.

[0050] In some embodiments, the lubricant has a kinematic viscosity in the range of 10-1000 cSt when measured at a temperature of 25°C.

[0051] It may be that the lubricant has a kinematic viscosity in the range 25-750 cSt, 50-500 cSt or 100-300 cSt, when measured at a temperature of 25°C. The use of lubricants within the range claimed exhibits beneficial healing abilities upon damage to the surface coating, e.g. any surface damage heals faster than if a lubricant having viscosity outside this range is used.

[0052] It may be that the lubricant has a kinematic viscosity in the range 50-300 cSt. Such low viscosity lubricants generally make less robust surface coatings. The surface coating of the present invention advantageously allows for the use of low viscosity lubricants; the lubricant molecules of the low viscosity lubricants are held strongly within the pores of the reticulated structure and are hard to remove. Kinematic viscosity can be measured using, for example, ASTM D445-24.

[0053] In some embodiments, the pore apertures of the reticulated structure have a diameter within the range of 1 to 20 A.

[0054] It may be that the reticulated structure is microporous. As is commonly understood in the field, a microporous material has pores with dimensions below 2nm. The microporosity of the reticulated structure (i.e. having pores with apertures within the range of 1 to 20 A) creates high capillary forces, which contribute to retention of the lubricant within the pores of the reticulated structure.

[0055] The high capillary forces created by the microporosity of the reticulated structure act together with the matching of the lubricant molecules chain diameter and the pore aperture diameter to insert the lubricant molecules within the pores of the reticulated structure synergistically to improve retention of the lubricant molecules within the pores and to increase the robustness of the surface coating, and the longevity of the low-friction properties it exhibits.

[0056] The high capillary forces created by the microporosity of the reticulated structure acts together with the functional group of the reticulated structure and / or the functional group of the lubricant molecules synergistically to improve retention of the lubricant molecules within the pores of the reticulated structure and to increase the robustness of the surface coating, and the longevity of the low-friction properties it exhibits.

[0057] All three of: (i) the matching of the lubricant molecules chain diameter and the pore aperture diameter to insert the lubricant molecules into the pores of the reticulated structure; (ii) the high capillary forces created by the microporosity (e.g. with pore aperture diameters of 1 to 20 A) of the reticulated structure; and (iii) the functional group of the reticulated structure and / or the functional group of the lubricant molecules act together synergistically to improve retention of the lubricant molecules within the pores of 008864365

[0058] 9 the reticulated structure and to increase the robustness of the surface coating, and the longevity of the low-friction properties it exhibits.

[0059] In some embodiments, the reticulated structure is a metal-organic framework having pores.

[0060] It may be that the metal-organic framework (MOF) comprises: metal ions selected from Zr, Zn, Al, Fe, Cr, Cu and Ti; and linker groups having the structure according to formula (I) wherein A is one or more groups selected from: an aryl group, a heteroaryl group, an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group and a heterocyclic group, each of which may be substituted with one or more groups selected from alkyl, alkenyl, alkynyl, amino, halo or hydroxyl.

[0061] L is a ligation group, each independently selected from carboxyl, hydroxyl and 5- or 6-membered heteroaryl having from 1 to 3 nitrogen heteroatoms; and n is an integer in the range from 0 to 6.

[0062] It may be that the metal ions are selected from the group consisting of Zr3+, Zr4+, Zn2+, Al3+, Fe2+, Fe3+, Cr2+, Cr3+, Cr6+, Cu+, Cu2+, Ti3+and Ti4+. It may be that the MOF comprises only a single type of metal ion. The skilled person is aware of appropriate metal salts which may be used to obtain the required metal ions. For example, the respective halide may be used. The metal ion may be derived from a metal salt selected from a chloride of any of the above-recited metal ions.

[0063] It may be that A is selected from a C5-C30 aryl group, a C3-C29 heteroaryl group, a C1-C30 alkyl group, a C2-C30 alkenyl group, a C2-C30 alkynyl group, a C3-C30 cycloalkyl group, and a C2-C29 heterocyclic group. It may be that A is Ce-18 aryl. It may be that A is selected from phenyl, naphthalene, biphenyl, fluorene, anthracene, phenanthrene, phenalene, terphenyl, tetracene, chrysene, triphenylene, pyrene, pentacene, perylene, benzo[a]pyrene, corannulene, and coronene. It may be that A is selected from a Ce aryl group, and a C3 heteroaryl. It maybe that A is benzene or imidazole. It may be that A comprises two or more Ce phenyl rings linked together by single bonds; preferably the two or more phenyl rings are bonded together in a linear manner. In some cases, A is selected from phenyl, biphenyl, and terphenyl (preferably paraterphenyl).

[0064] The group L is a ligation group each of which is independently selected from carboxyl, hydroxyl and 5- or 6-membered heteroaryl having from 1 to 3 nitrogen heteroatoms. The 5- or 6-membered heteroaryl having from 1 to 3 nitrogen heteroatoms may be, for example, pyrrole, imidazole, pyrazole, triazole, pyridine, diazine, and triazine. It may be that the ligation groups are each selected from carboxyl and hydroxyl; preferably carboxyl. It may be that all of the ligation groups in the linker group are the same. 008864365

[0065] 10

[0066] The integer n defines the number of ligation groups attached to each A group and is in the range 0-6. It may be that n is 2-3, it may be that n is 2. In the case where n is 0, the group A is capable of ligating to the metal ion to form the MOF, in place of a separate ligation group, L.

[0067] It may be that the linker group is selected from benzodicarboxylic acid, biphenyldicarboxylic acid, or terphenyldicarboxylic acid; optionally substituted with one or more groups selected from amino, halo, hydroxyl, nitro, azido, and C2-4 alkynyl and cyclooctynyl; it may be that the optional substituents are selected from amino and hydroxyl.

[0068] It may be that the linker is selected from one of the following molecules: 1 ,4-benzodicarboxylic acid, 4,4"-biphenyldicarboxylic acid and p-terphenyl-4,4"-dicarboxylic acid, optionally the linker is substituted with one or more groups selected from OH and NH2.

[0069] For example, the linker may be selected from: 2,5-dihydroxy-1 ,4-benzenedicarboxylic acid, 2,5-diamino-

[0070] 1 .4-benzenedicarboxylic acid, 2,2’-dihydroxy-4,4'-biphenyldicarboxylic acid, 3,3’-dihydroxy- 4,4'-biphenyldicarboxylic acid, 2,2’-diamino-4,4'-biphenyldicarboxylic acid, 3,3’-amino- 4,4'-biphenyldicarboxylic acid, 2,2”-dihydroxy-p-terphenyl-4,4"-dicarboxylic acid, 2,2”-diamino-p- terphenyl-4,4"-dicarboxylic acid, 3,3”-dihydroxy-p-terphenyl-4,4"-dicarboxylic acid, 3,3”-diamino-p- terphenyl-4,4"-dicarboxylic acid, and 2’,5’-dihydroxy-[1 ,1 ’:4’,1 ”]-terphenyl-4,4"-dicarboxylic acid.

[0071] It may be that the linker is 2,5-dihydroxy-1 ,4-benzenedicarboxylic acid.

[0072] It may be that the combination of metal ion and linker is chosen to generate one of the following MOFs: Zr(UiO-66-OH) [that is, Zr4+with 2, 5-dihydroxy-1 ,4-benzenedicarboxylic acid linker], Zr(UiO-66-NH2) [that is, Zr4+with 2,5-diamino-1 ,4-benzenedicarboxylic acid linker or with 2-aminoterepthalic acid], Zr(UiO-67- OH) [that is, Zr4+with 3,3’-dihydroxy-4,4'-biphenyldicarboxylic acid linker], Zr(UiO-67- NH2) [that is, Zr4+with 3,3’-amino-4,4'-biphenyldicarboxylic acid linker], Zr(UiO-68-OH) [that is, Zr4+with 3,3”-dihydroxy-p- terphenyl-4,4"-dicarboxylic acid linker], and Zr(UiO-68- NH2) [that is, Zr4+with 3,3”-diamino-p-terphenyl- 4,4"-dicarboxylic acid linker].

[0073] It may be that, the metal ion and linker is chosen to generate the MOF Zr(UiO-66-OH), that is Zr4+with

[0074] 2.5-dihydroxy-1 ,4-benzenedicarboxylic acid linker.

[0075] If the reticulated structure is a MOF, and a functional group (below: FG) is added to the reticulated structure, it may be that, for example, the hydroxy or amino groups in such a MOF are used to add the functional group. The functional groups are as described elsewhere herein. For example, the MOFs used in the surface coating may be one of the following: Zr(UiO-66-O-FG) [that is, Zr4+with 2,5-dihydroxy-1 ,4- benzenedicarboxylic acid linker, where one or more hydroxy groups are substituted with a functional group (FG) as described above], Zr(UiO-66-NHFG) [that is, Zr4+with 2, 5-diamino-1 ,4-benzenedicarboxylic acid linker or with 2-aminoterepthalic acid, with one or more amino groups substituted with a functional group (FG) as described above], Zr(UiO-67-OFG) [that is, Zr4+with 3,3’-dihydroxy- 4,4'-biphenyldicarboxylic acid linker, where one or more hydroxy groups are substituted with a functional group (FG) as described above], Zr(UiO-67- NHFG) [that is, Zr4+with 3,3’-amino-4,4'-biphenyldicarboxylic acid linker, with one or more amino groups substituted with a functional group (FG) as described above], 008864365

[0076] 11

[0077] Zr(UiO-68-OFG) [that is, Zr4+with 3,3”-dihydroxy-p-terphenyl-4,4"-dicarboxylic acid linker, where one or more hydroxy groups are substituted with a functional group (FG) as described above], and Zr(UiO-68- NHFG) [that is, Zr4+with 3,3”-diamino-p-terphenyl-4,4"-dicarboxylic acid linker, with one or more amino groups substituted with a functional group (FG) as described above].

[0078] In some embodiments, the reticulated structure is a covalent organic framework having pores.

[0079] It may be that the covalent organic framework (COF) is an imine-based COF, a triazine-based COF, a p- ketoenamine-based COF, or a boron-based COF. The benefits described herein in relation to MOFs as the reticulated structure apply also to the use of COFs as the reticulated structure.

[0080] Imine-based COFs:

[0081] Amine monomer: p-Phenylenediamine (PDA) or, benzidine

[0082] Aldehyde monomer: 2,4,6-Trihydroxybenzene-1 ,3,5-Triformylbenzene or, terephthaldehyde (TP A)

[0083] Properties: Surface area = 500-2000 m2 / g, Pore size = 1 .5-4.5 nm

[0084] Triazine-based COFs:

[0085] Triazine monomer: 2,4,6-Tris(4-aminophenyl)-1 ,3,5-triazine (TAPT)

[0086] Aldehyde monomer: 1 ,3,5-Triformylbenzene (TFB) or, terephthaldehyde (TP A).

[0087] Properties: Surface area = 700-1500 m2 / g, Pore size = 1-2 nm

[0088] B-ketoenamine-based COFs:

[0089] Aromatic diamine: p-phenylenediamine (PDA), benzidine

[0090] Aldehyde monomer: 1 ,3,5-Triformylphloroglucinol (TFP)

[0091] Properties: Surface area = 900-2000 m2 / g, Pore size = 2-3 nm

[0092] In a second aspect, the present invention provides a substrate comprising the surface coating of the first aspect.

[0093] It may be that the substrate permits high optical transmission. For example, the optical transmission of the substrate may be greater than 70%, greater than 80% or greater than 90% to light having a wavelength in the range 400-700 nm. It may be that the substrate is a transparent material, such as glass or a transparent polymer (e.g. low density polyethylene (LDPE), high density polyethylene (HDPE), polyurethane (PU), polyethylene terephthalate (PET), polycarbonate (PC), polymethylmethacrylate (PMMA)). This optical transmissivity provides particular benefits, for example the ability to use the coatings to provide optically transmissive hydrophobic, oleophobic, or amphiphobic coatings. This may be beneficial, for example if applied to a substrate in a scenario where it is desired to be able to see the surface decoration of the substrate through the coating. This is also particularly beneficial when combined with optically transmissive, or transparent, substrates such as windows, windshields etc. where the beneficial coating properties can be achieved with minimal or no impairment to the optical transmissivity. 008864365

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[0095] It may be that the reticulated structures are partially optically transparent. In some examples, infusing the reticulated structure with lubricant, to hold the lubricant molecules within the pores of the reticulated structure, increases the transparency of the surface coating, relative to the reticulated structure in isolation.

[0096] It may be that the substrate is an aluminium substrate, for example an anodized aluminium substrate.

[0097] It may be that the reticulated structure of the surface coating on the substrate is prepared in a layer-by- layer fashion. Such preparation substantially eliminates the presence of interparticle gaps, and achieves a substantially defect free surface pattern which can improve lubricant retention, and improved durability of low-friction properties.

[0098] It may be that the surface coating has an average thickness of 50-500nm. The thickness may be measured by AFM, cross-section visualisation by SEM or by ellipsometry. It may be that the surface coating has an average thickness in the range 60-400nm, 70-300nm, 100-250nm, or 150-200nm.

[0099] It may be that the substrate is primed for growing the reticulated structure in a layer-by-layer fashion, for example, in the case of a MOF, through functionalisation of the substrate with an organic linker moiety. For example, in the case of an aluminium substrate, the aluminium substrate can be dipped into organic linker solution in dimethylformamide for 4 hours at 120°C. This process forms ester bonds between carboxyl functional groups in the linkers and hydroxyl functional groups on the aluminium substrate. This priming step ensures good adhesion of the reticulated structure to the substrate, leading to a more durable surface coating.

[0100] In a third aspect, the present invention provides a method of preparing the substrate of the second aspect, comprising the step of providing the reticulated structure on a surface of the substrate and subsequently infusing the reticulated structure with the lubricant.

[0101] It may be that the method of preparing the substrate of the second aspect, or a substrate according to the invention more generally comprises one or more of the steps of:

[0102] (i) providing a reticulated structure;

[0103] (ii) providing a lubricant comprising lubricant molecules which have a section capable of being held within a pore of the reticulated structure, whilst an adjacent section extends from a pore aperture thereof;

[0104] (iii) preparing the reticulated structure, either in particle form to be sprayed onto a substrate, or by growing the reticulated structure in a layer-by-layer fashion on the substrate;

[0105] (iv) if in step (iii) the reticulated structure is in particle form, spraying the particles onto the substrate;

[0106] (v) infusing the reticulated structure with lubricant, causing insertion of the lubricant molecules into the pores of the reticulated structure. 008864365

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[0108] Further, the method may optionally include, before lubricant infusion, and in the case of the reticulated structure being in particle form, either before or after spraying, the step of

[0109] (vi) functionalising the reticulated structure and / or lubricant molecules with functional groups as described above.

[0110] In a fourth aspect, the present invention provides a kit, comprising a reticulated structure that is a metalorganic framework having pores or a covalent organic framework having pores, and a lubricant comprising lubricant molecules, wherein the lubricant molecules comprise a section capable of being held within a pore of the reticulated structure, whilst an adjacent section extends from a pore aperture thereof.

[0111] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0112] Summary of the Figures

[0113] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0114] Figure 1. Schematics depicting the advantages of a rational combination of MOF pore size, surface chemistry and lubricant to enable size-dependent lubricant intercalation and strong oil entrapment on the surface. Left: Poor SLIPS design, where lubricant is not able to enter the MOF pore due to size mismatch and is adsorbed on the surface. Middle: successful intercalation into as-prepared MOF offering only physical confinement with limited stability. Right: intercalation in functionalised and size-matched pore with enhanced host-guest interactions for maximal robustness.

[0115] Figure 2. Capillary pressure of lubricants inside MOFs. Relationship between MOF pore radius and capillary pressure for different lubricants based on Young-Laplace equation. Pore radii for UiO-66 and UiO-67 are marked by two circles.

[0116] Figure 3. (A) SEM image showing morphology of the UiO-66 nanoparticles. (B) TEM image showing porosity of the UiO-66 nanoparticles. (C) SEM images showing morphology of a surface sprayed with the alkyl functionalised UiO-66 nanoparticles, followed by Fomblin infusion. (D) SEM image of surface grown alkyl functionalised UiO-66 on aluminium infused with Fomblin.

[0117] Figure 4. (A) FTIR and (B) PXRD graphs of NH2-UiO-66 and functionalised MOFs (A-UiO-66 and F-UiO- 66) confirming the successful synthesis and post-synthetic modifications. The marked peaks at 1380 cm-1in all three graphs indicate the presence of C-OH bond in the MOF linker. Peaks at 1690 cm-1indicate C=O stretching, confirming the covalent linkage of fluoro (in F-UiO-66) and alkyl (in A-UiO-66) chains to the amino functional group of hydrophilic NH2-UiO-66. Characteristic peaks at 1230 cm-1and 2926 cm-1for C-F and C-H stretching also confirmed the successful post-synthetic modifications. Retention of the characteristic peaks of UiO-66 crystalline structure in functionalised MOFs suggested that there the molecular arrangements remained unaltered. 008864365

[0118] 14

[0119] Figure 5. (A) FTIR and (B) PXRD graphs of NH2-UiO-67 and alkyl functionalised UiO-67 confirming the successful synthesis and post-synthetic modifications. Presence of C-N stretching confirmed the successful linkage of alkyl chains to the MOF linker.

[0120] Figure 6. (A) FTIR and (B) PXRD graphs of ZIF-8, NH2-MOF-5, and alkyl functionalised MOF-5 confirming the successful synthesis and post-synthetic modifications. C=N and C-H stretching peaks at 1583 cm-1and 2925 cm-1, respectively confirmed the chemical structure of ZIF-8. Specific FTIR peaks at 1377 cm-1and 1572 cm-1attributed to symmetric and asymmetric stretching of C-0 bonds in benzene ring confirmed the MOF-5 structure. The post-synthetic functionalisation of MOF-5 with alkyl chains was confirmed by C-N stretching peak at 2917 cm-1. PXRD spectra showed typical peaks of ZIF-8 and alkyl functionalised MOF-5 structures.

[0121] Figure 7. SEM images of F-UiO-66 (A) sprayed on metal substrate (aluminium) and (B) grown using L / L technique.

[0122] Figure 8. Thickness measurement using Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM). The thickness of (A) the sprayed and (B) L / L MOF samples (F-UiO-66) are estimated to be around ~20 pm and ~3 pm, respectively.

[0123] Figure 9. Insertion of lubricant chains in UiO-66 after NVT equilibration for 0.5 ns at 300K. (A) UiO-66 and Fomblin chains. (B) UiO-66 and silicone chains. (The translucent white blobs (labelled “MOF”) represent UiO-66, the darker, translucent shaded surface in (A) (labelled “Fomblin chains”) represents Fomblin and the darker, translucent shaded surface in (B) (labelled “Silicone chains”) represents silicone lubricant. Fomblin chain is observed adhered to UiO-66 due to strong interactions. In contrast, silicone chains struggled to adhere to the UiO-66 as the interactions between two silicone chains surpassed their interactions with MOFs. Yellow dotted line shows the boundary of two silicone chains).

[0124] Figure 10. Intercalation and confinement of Fomblin lubricant chain (larger circles) inside the octahedral UiO-66 pore (through triangular aperture is marked for clarity).

[0125] Figure 11. Schematic representation of functionalised UiO-66 and UiO-67 aperture sizes.

[0126] Figure 12. Investigation of pore size from ~4A - ~12A on the durability of silicone (Si500) SLIPS. ZIF-8, UiO-66, UiO-67 and MOF-5 were selected from Fig. 24 to study the effect of pore size on the SLIPS durability.

[0127] Figure 13. Change in the BET-surface area after successful infusion of silicone oil into UiO-67 pores.

[0128] Figure 14.13C-NMR spectra confirming intercalation of silicone oil into UiO-67 (upper) and UiO-66 (lower).

[0129] Figure 15. Raman spectra confirming intercalation of silicone oil into UiO-67 (upper) and UiO-66 (lower).

[0130] Figure 16. Contact angles measured on (A) NH2-UiO-66 < 10°, (B) A-UiO-66 = 122° ± 3° and (C) F-UiO-

[0131] 66 = 135° ± 3°. Scale bars are 1 mm. 008864365

[0132] 15

[0133] Figure 17. Change in A0 of various SLIPS with rotational speed (spinning rate (RPM)): (A) NH2-UiO-66, (B) A-UiO-66, and (C) F-UiO-66. Spinning speeds ranged from 100 RPM to 10000 RPM.

[0134] Figure 18. Spinning stability data of MOF-based SLIPS showing percentage loss in lubricant weight against spinning rate (RPM) for (A) NH2-UiO-66, (B) A-UiO-66, and (C) F-UiO-66.

[0135] Figure 19. SEM images of control boehmite sample (rough surface) prepared by etching in boiling water and imaged at different magnifications.

[0136] Figure 20. Water shedding test on SLIPS. The loss of lubricants mass caused by depletion from (A) NH2- UiO-66, (B) A-UiO-66, and (C) F-UiO-66 recorded for 10 water shedding cycles. The volume of water in each cycle is 50 mL.

[0137] Figure 21. The change in A0 caused by lubricant depletion from (A) NH2-UiO-66, (B) A-UiO-66, and (C) F-UiO-66 recorded for 10 water shedding cycles. The volume of water in each cycle is 50 mL.

[0138] Figure 22. Optical image of alkyl functionalised MOF-5 infused with Si500, showing large particles, > 50 pm in size.

[0139] Figure 23. SEM images of (A) ZIF-8, (B) NH2-UiO-66, (C) NH2-UiO-67 and (D) NH2-MOF-5 particles. A typical morphology was observed for each MOF type.

[0140] Figure 24. MOFs pore size and diameter of lubricant chains. Plot showing the diameters of silicone and Fomblin lubricant chains against the aperture size of the different MOFs including ZIF-11 , DUT-67, MIL- 100, MIL-101 , ZIF-8, UiO-66, MOF-5 and UiO-67. In respect of each lubricant shown, the leftmost of the two squares corresponds to ZIF-11 , the rightmost square corresponds to ZIF-8. The two leftmost circle corresponds to UiO-66, and the rightmost circle corresponds to UiO-67. The leftmost of the two five- pointed stars corresponds to MIL-100(Fe), the rightmost, five-pointed star corresponds to MIL-101 (Cr). In each case, “leftmost” corresponds to lower aperture size and “rightmost” corresponds to higher aperture size.

[0141] Figure 25. Molecular structures of functionalised UiO-66 MOF. Molecular structure of hydrophilic amino (NH2-UiO-66), alkyl (A-UiO-66), and fluoro functionalised (F-UiO-66) UiO-66.

[0142] Figure 26. Gradient isosurfaces for (A) amino functionalised linker and silicone chain, (B) alkyl functionalised linker and silicone chain and (C) fluoro functionalised linker with silicone chain. (D) Amino functionalised linker and Fomblin chain, (E) alkyl functionalised linker and Fomblin chain and (F) fluoro functionalised linker with Fomblin chain. Spheres represent different atoms: the lightest shaded is H, the darkest shaded is C, and the others are selected from O, N, F, and Si - the skilled person is able to determine these from the definitions of the molecules and the corresponding valencies of each atom. The two-way arrows marked “X” indicate the interaction between lubricants and functional groups.

[0143] Figure 27. Electrostatic potential (ESP) plots of (A) amino functionalised linker and silicone chain, (B) alkyl functionalised linker and silicone chain and (C) fluoro functionalised linker with silicone chain. (D) Amino functionalised linker and Fomblin chain, (E) alkyl functionalised linker and Fomblin chain and (F) fluoro functionalised linker with Fomblin chain. Light dots on the ESP surfaces represent electrostatic 008864365

[0144] 16 potential maxima and minima - the skilled person is able to distinguish maxima from minima based on the surrounding ESP fields and nearby atoms.

[0145] Figure 28. Contribution of the SAPT-derived constructive dispersion, electrostatic, induction and exchange forces towards interaction energy between different combinations of functionalised linkers and lubricant. -NH2, alkyl and fluoro represent amino functional group, alkyl chain and fluoro chain, respectively. The bars are shaded to show, from bottom to top, exchange, electrostatic, induction, and dispersion forces.

[0146] Figure 29. (A) Schematic illustration of AFM adhesion force measurement and (B) contact interface between tip, lubricant and MOF particle.

[0147] Figure 30. Representative force-distance curves of (A) NH2-UiO-66 and Fomblin and (B) A-UiO-66 and Fomblin. The approach and retract velocities were both 0.1 pm / s. The adhesion force was taken to be the difference between the baseline (0 N / m) and the largest negative normal force in the retract dataset. The approach curve is the upper line in each graph (with an arrow pointing upwards), and the retract curve is the lower line in each graph (with an arrow pointing downwards).

[0148] Figure 31. Lubricant-MOF adhesion forces obtained from AFM force-distance curves. Silicon tips are used as a control. For each set of three bars, the upper bar corresponds to the silicon tip, the middle to the Si50-coated, and the lower to the Fomblin-coated.

[0149] Figure 32. a) Comparative photographs of a glass substrate sprayed with functionalized modified MOF (F-UiO-66) particles (left) and the surface after infusing lubricant (right). Reduction in scattering with oil infusion is clear from the pictures, b) Transmittance of the dry functionalized MOF and corresponding SLIPS measured using UV-Vis spectroscopy.

[0150] Figure 33. Lubricant replenishment on F-UiO-66 SLIPS. The images are snapshots from videos, showing morphological changes before and after a given replenishment period. The average replenishment time for Si50, Si500 and Fomblin were 30 minutes, 180 minutes and 60 minutes, respectively. Surfaces infused with Si50 and Si500 were almost dried up after 3rd and 7th cycles. Depleted zones are marked with black dotted circles. Scale bars are 1 cm.

[0151] Figure 34. Change in A0 on F-UiO-66 infused with different lubricants measured immediately following water shedding cycles (dotted lines) and after recovery period (solid lines, labelled “-R” in legend).

[0152] Figure 35. Lubricant stability (measured as oil mass percentage) of Fomblin on NH2-UiO-66, A-UiO-66 and F-UiO-66 surfaces tested over 20 water shedding cycles.

[0153] Figure 36. Evolution of the lubricant (Fomblin) mass (moil) normalised with mass of MOF particles, with shedding cycles capturing final oil retention. Dashed line shows the theoretical loading capacity of UiO-66 for Fomblin. The (retained) lubricant mass for the two hydrophobic MOFs plateaus down to a higher threshold and never falls down to the shaded area under the theoretical capacity for the pristine (unfunctionalised) MOF. 008864365

[0154] 17

[0155] Figure 37. Wetting angles (0Adv, sliding and A0) for the Fomblin based SLIPS on different UiO-66 MOFs, measured after reaching the plateau in the lubricant content.

[0156] Figure 38. Schematic representation of the lubricant immobilisation inside frameworks and the formation of a supramolecular structure, which contributes to the excellent stability of the SLIPS described herein.

[0157] Figure 39. Diagrammatic representation of the supramolecular structure of the lubricant infused MOF particle.

[0158] Figure 40. Lubricant retention and surface slipperiness was tracked by measuring average droplet sliding velocity (Vavg) on the surface (solid lines) and A0 (dotted lines) over a long (50 hrs) water shedding (dripping water drops) testing on Fomblin / A-UiO-66 and Fomblin / F-UiO-66.

[0159] Figure 41. FTIR spectra showing shift in C-F stretching in Fomblin after interacting with fluorine atoms in F-UiO-66, confirming strong intermolecular interactions. No shift was observed in other MOFs. At the 1118 cm1stretch, the magnitude of the peak for the samples is in the decreasing order: F-UiO- 66 / Fomblin > A-UiO-66 / Fomblin > Fomblin > NH2-UiO-66 / Fomblin. At the 1122 cm1stretch, the magnitude of the peak for the samples is in the decreasing order: A-UiO-66 / Fomblin > F-UiO-66 / Fomblin > Fomblin > NH2-UiO-66 / Fomblin.

[0160] Figure 42. Evolution of surface slipperiness (droplet velocity and A0) over 12 hrs water shedding test on Si500 / A-UiO-67. The control line has the steepest initial gradient in both graphs, then A-UiO-66, then A- UiO-67.

[0161] Figure 43. Comparison of the A-UiO-67 / Si500 and F-UiO-66 / Fomblin SLIPS described herein against state-of-the-art SLIPS in terms of stability against dripping water. See part 4.4.1 of the Detailed Methods for details.

[0162] Figure 44. Images from cloaking experiments showing wetting ridges on F-UiO-66 / Fomblin and A-UiO- 67 / Si500 SLIPS before and after water shedding experiments. The water droplets were still able to slide on the surfaces albeit at slower speed.

[0163] Figure 45. Optical images showing wetting ridge formation on L / L F-UiO-66 / Fomblin SLIPS, before and after water shedding test. Inset shows micro oil droplets and clear wetting ridge on the interface of 10 pL water drop placed at freshly infused surface. No wetting ridge or cloaking was observed after long-term (50 hrs) shedding while the surface still maintained its slipperiness. Scale bar is 200 pm.

[0164] Figure 46. a) Fresh F-UiO-66 / Fomblin SLIPS and b) after 50 hrs of continuous water shedding. Lubricant depleted region is visible as faded spot in the middle of the sample.

[0165] Figure 47. Waterjet (nozzle diameter = 2.5 mm) impacting at ~35 m / s.

[0166] Figure 48. Free sliding of water droplet after three repeated jet tests on F-UiO-66 / Fomblin SLIPS. Scale bars are 1 mm. 008864365

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[0168] Figure 49. Surface assessment after jet impact, a) Free sliding of water droplet from the impact site after repeated jet impacts on F-UiO-66 / Fomblin SLIPS (scale bar: 1 cm), b) SEM images showing morphological changes at the impact site.

[0169] Figure 50. Effect of continuous water shedding on ice adhesion strength on control surface (rough aluminium / Si500) and other MOF / lubricant combinations.

[0170] Figure 51. Ice adhesion strength measured before and after high-speed waterjets (~35 m / s) on different SLIPS and compared with control surface.

[0171] Figure 52. Ice adhesion strength comparison of robust SLIPS described herein (F-UiO-66 / Fomblin) against previously reported MOF-based SLIPS to confirm their poor design.

[0172] Figure 53. SEM and EDS spectra of (A) F-UiO-66 / Fomblin SLIPS, and two controls, including (B) AI / Si500 and (C) NeverWet®, subjected to dynamic anti-fouling tests for 96 hrs at 25 °C.

[0173] Figure 54. SEM images of the (A) PTFE, (B) NeverWet®, (C) AI / Si500 and (D) F-UiO-66 / Fomblin recorded after 6 hrs of incubation. Deposition of bacteria (S. aureus) could be readily observed on the control samples.

[0174] Figure 55. SEM images of (i) PTFE, (ii) commercial NeverWet®, (iii) AI / Si500 and (iv) F-UiO-66 / Fomblin showing biofilm formation after 50 hrs of incubation under the continuous flow of S. aureus culture.

[0175] Figure 56. Surface coverage of biofilm, quantified using by Imaged software, of PTFE, commercial NeverWet®, AI / Si500 and F-UiO-66 / Fomblin after 50 hrs of incubation under the continuous flow of S. aureus culture. In each set of four bars, the bars represent, from left to right, F-UiO-66 / Fomblin, AI / Si500, PTFE, and NeverWet®.

[0176] Figure 57. Optimised molecular structures of MOF and lubricants. (A) NH2-UiO-66, (B) Fomblin chain and (C) Silicone chain. Hydrogen atoms bonded to MOFs have been omitted for clarity.

[0177] Figure 58. (A) Schematic representation and (B) photograph of closed-loop 3D printed chamber used for dynamic anti-fouling and anti-biofouling tests.

[0178] Detailed Description of the Invention

[0179] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0180] Described herein is a rational SLIPS design which accounts for a combination of physical and chemical interactions to mitigate or overcome cloaking and shear forces from sliding drops / liquid that cause the lubricant depletion (Fig. 1)10. It is understood that reference to MOFs herein may be replaced with reference to COFs, and the same or similar properties and benefits would be expected. 008864365

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[0182] A rational, three-fold strategy is described for enhancing the lubricant-substrate interactions. Each part of the three-fold strategy is independently advantageous in improving the lubricant-substrate interactions. First, use of a microporous reticulated structure (MOFs or COFs), for example with sub-nanometre pores, helps to enable extremely high capillary forces between lubricant (e.g. oil) and the surface coating (Fig. 2). Second, a reticulated structure (MOF or COF) having an aperture size appropriately selected to fit the diameter of the lubricant molecular chain helps to enable sufficient insertion or intercalation of the lubricant into aligned pores. Third, functionalisation of the pores of the reticulated structure and / or functionalisation of the lubricant molecules (e.g., via post-synthetic modification of the MOF / COF organic linkers) helps to facilitate a strong host-guest interaction between the reticulated structure and the lubricant, and to elicit formation of supramolecular structure. This three-fold strategy has not previously been considered in the art, and is useful in achieving insertion (which herein can be described as nanoconfinement, intercalation or entrapment) of lubricants into the reticulated structure and the excellent robustness of the presently described SLIPS.

[0183] To establish this rational approach, a range of MOFs with different pore sizes (ZIF-8, UiO-66, UiO-67 and MOF-5) and chemistries (-NH2, -CH3 and -CF3) were synthesised (see part 3.2-3.5. of the Detailed Methods) and used in combination with various lubricants (silicone, Krytox and Fomblin). SLIPS were prepared by infusing lubricants into MOF particles which had either been sprayed onto a substrate (“sprayed” MOF) or grown on a substrate using layer-by-layer (L / L) technique (herein referred to as a “grown” or “L / L” MOF), the grown MOF resulting in better mechanical integrity of the MOF layer. To determine the desirable surface chemistry, in the case of sprayed MOF, the particles were functionalised before spraying, and, in the case of grown MOF, the L / L MOF was modified by post-synthetic functionalisation (see Brief Methods and part 3.5 of the Detailed Methods for details).

[0184] Scanning electron microscope (SEM) images of UiO-66 MOF nanoparticles are presented in Fig. 3A and Fig. 23. The chemical structures of the lubricants (silicone, Krytox and Fomblin) are summarised below, and the physical properties of the lubricants are summarised in Table 1 in part 3.8 of the Detailed

[0185] Fomblin

[0186] The microporous structure of the UiO-66 nanoparticles (Fig. 3B) was confirmed using transmission electron microscope (TEM). The corresponding chemical and crystalline structures before and after functionalisation were confirmed by Fourier transform infrared spectroscopy (FTIR) and powder X-ray 008864365

[0187] 20 diffraction (PXRD) (Figs. 4-6). The specific peaks at 1690 cm1, 1230 cm1and 2926 cm1in FTIR spectra can be attributed to stretching of the C=O, C-F and C-H bonds, respectively, confirming the successful linkage of alkyl (n = 8) and fluoro (n = 7) chains to the MOF linkers. The consistency of the main diffraction peaks in PXRD patterns of functionalised UiO-66 (Figs. 4B, 5B and 6B) suggest that the substituted side chains did not alter the MOF crystal structure24 26. Morphologies of sprayed and L / L surface-grown UiO-66 MOF on aluminium are presented in Fig. 3C, 3D, and 7. Fig. 3C shows the highly uniform surface obtained from sprayed MOF nanoparticles and as expected, the sprayed surface was relatively rough in comparison with the L / L surface grown MOF in Fig. 3D. Height profiles of the sprayed (~10 pm thick) and L / L grown UiO-66 MOF surface (~2-3 pm) on a metal substrate were obtained using focused ion beam SEM (Fig. 8).

[0188] Example 1 - Lubricant Nanoconfinement

[0189] To investigate lubricant nanoconfinement (e.g., oil nanoconfinement), SLIPS comprising silicone oil (Si50 and Si500) and fluorinated lubricants (Fomblin and Krytox) infused into pristine UiO-66, without any functionalisation, were prepared. The aperture size of UiO-66 is around 6 A27. The capillary pressure (Pcap) for UiO-66 pores was estimated using the Young-Laplace equation (see part 4.1 .1 of the Detailed Methods and Fig. 2). The water droplet advancing contact angle (0Adv) and contact angle hysteresis (A0) were measured for SLIPS with the four different lubricants (Si50, Si500, Krytox, Fomblin) infused in UiO- 66 (Table 3 in part 3.12 of the Detailed Methods).

[0190] To test stability, the prepared SLIPS were subject to water shedding, which involves dripping water drops on the tilted surfaces (45°) and allowing them (the drops) to slide off. The shedding test was performed in cycles wherein each cycle consisted of dripping 50 mL water (over ~60 min time span) as droplets followed by contact angle measurements either immediately afterwards or after a certain period of time (“recovery period”) in which the infused oil was left to recover. The sliding water droplets gradually deplete the lubricant from the surface through shear forces and / or encapsulation of the droplet by the lubricant film10(so-called “cloaking”) (see part 3.12 of the Detailed Methods). The SLIPS prepared from the pristine UiO-66 failed quickly; the droplets started to get pinned on the corresponding silicone-based SLIPS within first hour of shedding test whereas the ones with fluorinated lubricants performed slightly better, sustaining slipperiness for -4 hr (see Table 3 in part 3.12 of the Detailed Methods). To understand this early failure and differences among silicone and fluorinated oil infused surfaces, the intercalation of lubricant chains into the highly organised UiO-66 pores2829was investigated using molecular dynamic (MD) simulations and a series of experiments. A long-time MD simulation (see section 4.1.2 of the Detailed Methods) made it clear that the silicone chain was too large to enter the UiO-66 pores (Fig. 9) whereas the Fomblin chain could (Fig. 10). The lubricant chain diameters, calculated as the sum of branch bond lengths (calculated after structure optimization using quantum method PM7) were 2.76 A for Fomblin and -5.92 A for the silicone, which explain the differences in their intercalation in UiO-66. Additionally, and as expected, the silicone chain could fit comfortably in the bigger pore (~ 8 A) of UiO-67 (Figs. 11-12). To verify this simple geometric argument experimentally, a similar approach (see part 3.8 of 008864365

[0191] 21 the Detailed Methods) was used to infuse Si500 lubricant into UiO-66 and UiO-67 nanoparticles and analysed using various techniques such as BET-surface area and13C-NMR and Raman Spectroscopy. Following silicone oil infusion, the BET-surface area reduced by 98.3% in UiO-67 and only by 3.8% in UiO-66, which indirectly indicates the penetration of the lubricant into the UiO-67 pores with bigger aperture (Fig. 13). The presence of Si-Me carbon peak at ~1 ppm in UiO-6713C solid state NMR spectra indicates successful loading of the lubricant chain into the MOF pore (Fig. 14). Similarly, the Raman spectra in Fig. 15 shows a clear peak at 411 cm1, attributed to the Si-0 stretching, which is clearly distinct from the UiO-67 MOF characteristic peaks at 1610 cm1(C=C aromatic stretching), 1443 cm1(carboxylate OCO symmetric stretching), 1286 cm1(C-C inter-ring stretching), 1150 cm1(C-C symmetric ring breathing in linker) and 628 cm1(C-C-C aromatic ring in plane bending). This further indicates successful intercalation of the lubricant into the UiO-67 pores. The importance of this lubricant / pore size consistency was also verified using water shedding test (see Table 4 in part 3.1 .2 of the Detailed Methods). The combinations of UiO-66 / Fomblin and UiO-67 / Si500 maintained slipperiness (A0 <10°) for up to 3-4 water shedding cycles, well beyond less than one cycle for UiO-66 / Si500, underscoring the size dependence of intercalation and its role in enhancing the SLIPS durability. As an additional and indirect indication, 0Advfor the UiO-66 / Fomblin and UiO-67 / Si500 combination remained at -90° and -40° even after 10 continuous water cycles. This was in sharp contrast to the pristine MOF surfaces, before any lubricant infusion, which were superhydrophilic and showed a hemi-wicking behaviour when a water droplet was placed on them. The finite values of 0Adv measured even after multiple shedding cycles strongly point to size dependent intercalation. This testing illustrates the advantages of using a microporous reticulated structure. It also illustrates the advantages of using a lubricant including lubricant molecules with a section that has a maximum chain diameter which is a suitable size for the pores of the reticulated structure.

[0192] Example 2 - MOF pore chemistry for enhanced guest-host interactions

[0193] In a departure from pristine MOF, the effect of pore chemistry on SLIPS durability was investigated through a series of experiments and interaction energy calculations using density functional theory (DFT).

[0194] First, exploiting the well-known designability of MOFs30, the pores of UiO-66 were modified by covalently attaching low-energy molecular chains (see part 3.5 of the Detailed Methods), which could engender host-guest intermolecular interactions (e.g. dipole-dipole interactions, Debye force, and London dispersion forces). The hydrophilic UiO-66 (with -NH2 functionalised linker) is designated as NH2-UiO-66, whereas that functionalised with hydrophobic alkyl (-CH3, with n = 8 carbons; linear) and fluoro (-CF3, heptafluorobutyl; linear) chains are abbreviated as A-UiO-66 and F-UiO-66, respectively. The water drop contact angle measured of sprayed nanoparticles of NH2-UiO-66, A-UiO-66 and F-UiO-66 were <10°, 122° ± 3° and 135° ± 2°, respectively (Fig. 16). Each of these were then infused with lubricants Si50, Si500, Krytox and Fomblin, followed by wettability and water shedding test (Table 5 in part 3.12 of the Detailed Methods). No significant difference in the stability was observed between these SLIPS with Krytox and Fomblin, which have similar chemical structure. Hence, Krytox was excluded from rest of the 008864365

[0195] 22 tests. Lubricant retention on the sprayed UiO-66 MOFs was then assessed using centrifugation (see part 3.11 of the Detailed Methods) by subjecting the surfaces to spinning speeds ranging from 100 to 10,000 RPM for 60 s followed by measurement of mass change and contact angles (Figs. 17-18). Here the control surface was a rough boehmite substrate infused with Si500 (see part 3.9 of the Detailed Methods and Fig. 19 for fabrication details). The control surface suffered rapid lubricant depletion at just -1 ,000 RPM. In contrast, all UiO-66 (hydrophilic and hydrophobic) based SLIPS retained -50-60% oil even after spinning at 10,000 RPM and maintained self-cleaning property, i.e. A0 <10°.

[0196] Lubricant drainage (mass loss) and evolution of surface wettability were assessed using water shedding test (Figs. 20-21). For NH2-UiO-66 / silicone combinations, A0 increased dramatically after one shedding cycle; from -2° to -19° and from -3° to -15° for Si50 and Si500, respectively (Fig. 21). Fomblin infused into hydrophobic UiO-66 MOFs showed much better resistance to water shedding, possibly, due to strong interactions of the oil with the surface functional groups i.e. -CHs and -CF3 which may also help avoid cloaking of the water droplets and help retain the oil better31. SLIPS with hydrophobic UiO-66 infused with silicone lubricants were less stable, with Si500 fairing slightly better and retaining the slippery behaviour for 4 or 5 cycles. The larger size of silicone chains compared to smaller pores of UiO-66 will again make intercalation challenging, thus it is thought that the 4 or 5 cycles of stability largely results from oil adsorption and retention in between the MOF nanoparticles (i.e. interparticle spaces) as a whole. To further verify the geometric compatibility, different MOFs with pores in 4 A to 12 A range, such as ZIF-8 (4 A), A-UiO-66 (6 A), A-UiO-67 (8.3 A) and A-MOF-5 (12 A) were investigated with silicone (Si500) lubricant. As expected, for MOFs with smaller pores (ZIF-8 and A-UiO-66), where silicone should not penetrate, the SLIPS failed within first shedding cycle (Fig. 12). In contrast, Si500 based SLIPS with bigger MOF pores, e.g. A-UiO-67 and A-MOF-5, preserved their slipperiness (A0 <10°) for at least 8 water shedding cycles. The slightly earlier failure of the SLIPS prepared from A-MOF-5 (Fig. 22) is perhaps due to large interparticle gaps among inherent large crystals (-10 pm, see Fig. 22, Fig. 23D). Fig. 24 summarises the relevance of pore sizes of different MOFs against the diameters of the silicone and Fomblin chains, and is useful in guiding MOF based SLIPS design.

[0197] To investigate host-guest interactions, surface energies and the interactions between different lubricants and the MOF functional groups were examined. Contact angle measurements combined with Lifshitz-van der Waals / acid-base (LW / AB) method32showed the expected surface energy trend for functional groups: -NH2 > -CH3 > -CF3 (see part 4.2.1 of the Detailed Methods). This suggests easy wetting of MOFs having a -NH2 terminated linker with oils (due to their low surface energy), but that does not necessarily point to a strong interaction. Thus, for deeper insight, the different UiO-66 functionalisations (Fig. 25) and lubricant combinations were investigated both theoretically using DFT (see part 4.2.2 of the Detailed Methods) and experimentally using an atomic force microscope (AFM) (see part 4.2.5 of the Detailed Methods). Electron density and its derivatives obtained from DFT were first used to compute reduced density gradient (RDG) function33. RDG was then used to analyse and visualise the strength of noncovalent interactions. The corresponding interaction isosurfaces for different combinations of lubricant and UiO-66 linkers (with different functional groups) are shown in Fig. 26. The location of the isosurfaces in Fig. 26, particularly those indicated by the double-sided arrows labelled “X”, offer some critical insight 008864365

[0198] 23 into which molecular groups have van der Waals interaction. For example, with a hydrophilic (-NH2) group added to the MOF linker, the isosurface appears between the linker benzene ring and the methyl (Fig.

[0199] 26A) or fluoro (Fig. 26D) group in the lubricants. On the other hand, it appears between the methyl groups from alkyl functionalised linker and the silicone oil (e.g. Fig. 26B) or perfluoro groups in Fomblin and fluoro functionalised linker (e.g. Fig. 26F). Similarly, electrostatic potential (ESP) was calculated using the DFT data (see part 4.2.3. of the Detailed Methods and Fig. 27), which captures the progressive changes in the electrostatic potentials for different lubricant / linker functionalisation combinations. Overall, these point to electropositive nature of methyl groups and strong electronegativity introduced by fluorinated groups. However, the individual interaction components are unclear. Therefore, symmetry-adapted perturbation theory (SAPT) was used to identify the contributions from electrostatic, dispersion (London), induction (Debye) and exchange (repulsion) interaction (Fig. 28) (see part 4.2.4. of the Detailed Methods). In agreement with the results from RDG calculations in Fig. 26, the sum of dispersion and induction (i.e. van der Waals) interactions in Fig. 28 is markedly greater for each lubricant chain and hydrophobic linker combination compared to that for the hydrophilic linker. Additionally, the electrostatic interaction in Fig. 28 is highest for alkylated linker and silicone oil. Overall, the DFT results point to an advantage in matching the functional groups grafted to the MOF linker with those in lubricant carbon chain rather than simply relying on surface energy calculations. Although clearly offering clarity on the nature / types of oil and MOF interactions, the DFT calculations are naturally constrained by computational costs. Indeed, it was only possible to use limited lubricant chain length (i.e. number of carbon atoms) and thus is unable to offer a quantitative assessment of the lubricant and MOF interactions (see part 4.2 of the Detailed Methods). Therefore, the lubricant / MOF adhesion forces were measured using AFM (Figs. 29-30). The force-distance curves obtained using lubricant coated silicon tips and MOF particles were used to calculate the adhesion forces (see the methodology details in part 4.2.5 of the Detailed Methods). Measurement using dry silicon tips and UiO-66 particle was used as control. Only the relatively low viscosity lubricants (Si50 and Fomblin) were used to avoid errors due to formation of stable capillary bridge between the AFM tip and the MOF particles. Overall, these measurements point to adhesion (interaction) forces decreasing in the order F-UiO-66 / Si50 > A-UiO-66 / Si50 > A-UiO-66 / Fomblin > F-UiO- 66 / Fomblin » NH2-UiO-66 / Si50 > NH2-UiO-66 / Fomblin (Fig. 31). The results indicate that matching the surface functionalisation of the reticulated structure with the lubricant chemistry, or vice-versa, could significantly enhance the host-guest interactions (e.g., A-UiO-66 / silicone and F-UiO-66 / Fomblin).

[0200] Lastly, as a further indirect indication of the lubricant intercalation, the infusion of oil into MOF should alter the roughness and light scattering property, thereby also influencing the optical transparency of the surfaces. This was apparent for all exemplified SLIPS. For example, for F-UiO-66 / Fomblin combination, before and after lubricant infusion, the surfaces exhibited respectively <80 and >90% transmittance in visible spectrum (Fig. 32). 008864365

[0201] 24

[0202] Example 3 - Lubricant retention and replenishment

[0203] The reticulated porosity of MOFs and COFs offers an additional benefit: any local drainage of lubricant may be replenished from neighbouring parts through seepage. This for example can enable ‘healing’ of the local damages introduced to the SLIPS from water drop shedding tests.

[0204] For proof-of-concept, SLIPS samples comprising F-UiO-66 infused with Si50, Si500 or Fomblin were used. Fig. 33 shows the gradual healing (due to seepage of the oil from neighbouring interparticle gaps and the MOF pores) following water shedding. To assess the recovery timescales, A0 was measured, both immediately following a water shedding cycle and after a certain recovery period (Fig. 34). A0 increased sharply from ~3° to -22° for the Si50 infused SLIPS immediately after the first cycle of water shedding. Likewise, A0 for SLIPS infused with Si500 increased from -2° to -15° after 4 cycles. In contrast, following a recovery period, A0 remained under -10° after 3 and 6 shedding cycles on the Si50 and Si500 infused SLIPS, respectively. The recovery periods for the Si50, Si500 and Fomblin were ~30 min, -180 min and -60 min, respectively (showing consistent increase with the oil viscosity). Following the recovery period, the surfaces were then subjected to another round of water shedding. With Si50, the surface became dry after the second shedding cycle. Si500, which has similar chemical composition to Si50 but higher viscosity, showed replenishment up to seven shedding cycles possibly due to high initial oil loading (Table 2 in part 3.8 of the Detailed Methods) and better shear resistance. The F-UiO- 66 / Fomblin combination demonstrated full recovery even after 10 water shedding cycles. Additionally, the depleted area of Fomblin was smaller than that for the silicone lubricants, possibly due to Fomblin’s excellent confinement in the F-UiO-66 nanopores, higher affinity to the functionalised UiO-66, and / or weaker interactions with water34.

[0205] The final (retained) Fomblin lubricant masses were -8%, -48% and -53% of the NH2-UiO-66, A-UiO-66 and F-UiO-66 masses, respectively (Fig. 35). After 10thcycle, the lubricant mass on A-UiO-66 and F-UiO- 66 started to plateau, whereas the NH2-UiO-66 showed unstable weight loss pattern (Fig. 36). Regardless of the functionalisation type, a certain amount of lubricant was permanently held; A-UiO-66 and F-UiO-66 retained slippery behaviours with low sliding angles of -20° and -15° and A0 of <13° and <10°, respectively. The contact angle remained -1 15° for both hydrophobic UiO-66 MOFs and decreased to -46° for the one NH2-UiO-66 (Fig. 37).

[0206] To explain the markedly superior stability of the SLIPS described herein - e.g., with a rational combination of lubricant chain size, MOF pore size and chemistry - the formation of a supramolecular structure is hypothesised (Figs. 1 , 38, and 39) in which the long lubricant chains are partially embedded in the porous MOF structure and the protruding part of the chains endows slippery behaviour. However, unlike traditional thermodynamically controlled (formation of kinetically stable bonds) assembly of supramolecular structure35 37, said hypothesised supramolecular structure is based on strong host-guest interactions. This is akin to the interaction present in cyclodextrin-based inclusion complexes3839. These findings are supported by high interaction energies calculated between the corresponding MOF functionalisation and lubricant combination (e.g. alky l / silicone and fluoro / Fomblin). Lubricant retention on the SLIPS was quantified and compared against the theoretical loading capacity of UiO-66 (0.72 g / g) for 008864365

[0207] 25

[0208] Fomblin (see part 4.3.2 of the Detailed Methods). The measured lubricant retention for NH2-UiO-66 was ~0.5 g / g (Fig. 36), i.e., below the theoretical limit. This suggests that although the Fomblin chains entering the MOF pores (molecular cages) may remain trapped, those partly intercalated, lying on the particle surface and between the particles may have been depleted away due to weak interactions between amino and fluoro groups (Fig. 28). Conversely, with functionalised MOF particles, it is though that only the chains from the interparticle spaces are depleted under water shedding while strong guest-host interactions lead to formation of a layer of partially intercalated chains into a supramolecular structure (see Fig. 36 and 38), which is firmly retained and results in a much higher retention capacity (>3 g / g) (Fig. 36).

[0209] For a long-term stability assessment, water shedding was performed for 50 hrs at 100 mL / hr and with drops impacting on the SLIPS at -80 cm / s droplets followed by sliding along the surface. Fig. 40 shows that F-UiO-66 performed slightly better (A0 -6°) than A-UiO-66 (A0 -12°) due to stronger interaction of Fomblin with F-UiO-66, in agreement with results presented before. A shift in characteristic peak of Fomblin (C-F stretching) from 1 ,122 cm1to 1 ,188 cm1after infusion into F-UiO-66 was also observed due to strong F-F interactions (Fig. 41). The average speed of the droplets sliding (Vavg) on the surfaces decreased from -1 .2 to -0.2 and -1 .6 to -0.4 cm / s on A-UiO-66 / Fomblin and F-UiO-66 / Fomblin, respectively, over the long test period. On the other hand, fluorine-free SLIPS (prepared using A-UiO-67 and Si500 combination) retained slippery behaviour for >12 hr of water shedding. In contrast, controls based on functionalised AI / Si500 and UiO-66 / Si500 failed within one hour (Fig. 42). The drop sliding speed on A-UiO-67 / Si500 decreased from -0.6 to -0.2 cm / s. This testing demonstrates advantages of a SLIPS having a lubricant held within the pores of a reticulated structure, especially when the size relationship of the lubricant and pore is taken into account, and also when the surface functionalisation of the reticulated structure and / or lubricant is considered. Such benefits apply to SLIPS made from MOFs and COFs.

[0210] Fig. 43 summarises the excellent performance of exemplified SLIPS of the present disclosure (both fluorinated, F-UiO-66 / Fomblin, and fluorine-free, A-UiO-67 / Si500), prepared using sprayed nanoparticles, against comparative state-of-the-art SLIPS9 16 184041, which survived only a couple of hours at most and sometimes as little as tens of seconds.

[0211] Example 4 - SLIPS Robustness

[0212] Cloaking of the sliding water droplet by the lubricants was investigated. Obvious cloaking, including wetting ridge, was observed before water shedding tests (Fig. 44). However, after shedding tests, a clear and sharp contact line without any wetting ridge is observed on both SLIPS (see Fig. 45). Given that the drops still slide, retention of lubricants is clear. This retained slipperiness (Vavg >0) of these exemplified SLIPS point to their stability optimised through the three-pronged, rational approach described herein. A wetting ridge is a projection of the infused lubricant around a droplet of liquid being repelled by the surface. 008864365

[0213] 26

[0214] SLIPS prepared by infusing the (functionalised) sprayed MOF nanoparticles are good to assess physical and chemical characteristics, formation of supramolecular structure, and developing a rational strategy to promote lubricant retention. However, in some examples, layer-by-layer (L / L) grown MOFs may be used to impart increased overall mechanical robustness, since sprayed MOF particles are held only by relatively weaker van de Waals forces. There are a few advantages to this. First, due to absence of interparticle gaps, the reticulated structure of L / L MOF does not compromise the lubricant recovery discussed above. Second, the L / L MOF structure offers a defect-free surface pattern (e.g., pores in sub- nm size scale). The larger gap in sprayed MOFs may result in lower lubricant retention and, with depletion, the surface roughness may increase. This can eventually lead to a loss in surface smoothness which is an important property of SLIPS3. The results from long-term water shedding test performed on L / L MOF based SLIPS, for the same set of functionalisation / lubricant combinations as above, are shown in Fig. 46. On L / L F-UiO-66 / Fomblin SLIPS, after 50 hrs of shedding tests, the Vavg was ~0.5 cm / s, slightly faster than observed on the sprayed samples - this is reasonable since the L / L MOFs have a low (nano-hierarchical) roughness23- no cloaking and wetting ridge were observed (Fig. 45). For a much harsher test for SLIPS stability, the surfaces were subjected to high-speed waterjet impacting at -35 m / s (Figs. 47 and 48). Both fluorinated and fluorine-free SLIPS were able to resist jets up to -35 m / s (with the corresponding liquid Weber number -42,500, i.e., at least two orders of magnitude higher than any previous SLIPS). The surface slipperiness was assessed after three repeated jet impacts; water droplets readily slid off from the location of impact (Fig. 49a). The impact location was investigated using SEM, which showed superficial erosion and removal of the upper MOF layer without altering overall structure (Fig. 49b). This testing illustrates the desirable surface robustness of SLIPS using L / L MOFs. The benefits are also applicable to L / L COFs.

[0215] Example 5 - Anti-icing, anti-fouling and anti-biofouling

[0216] SLIPS using functionalised, L / L MOFs were tested for durability in various applications, which rely on their low adhesion properties (Figs. 50-52). An ultra-low ice adhesion strength of <10 kPa was observed on all rational SLIPS (i.e. both fluorinated and fluorine-free versions in Fig. 3D). As a measure of durability, the adhesion strength of the control SLIPS (rough aluminium / Si500) increased significantly from -2 kPa to -46 kPa after just 30 min of water shedding and to -24 kPa after single waterjet impact, respectively (Fig. 50 and Fig. 51). In contrast, the ice adhesion strength on the exemplified SLIPS (F-UiO-66 / Fomblin, A-UiO-66 / Fomblin, and A-UiO-67 / Si500) remained under 5 kPa after repeated high-speed jet impact tests (Fig. 51). Furthermore, the exemplified SLIPS maintained the ultra-low ice adhesion tested for 50 continuous icing / de-icing cycles, whereas, the comparative state-of-the-art MOF-based SLIPS23failed to preserve anti-icing characteristics after 20 cycles (Fig. 52).

[0217] The F-UiO-66 / Fomblin SLIPS was also tested for dynamic anti-fouling and anti-biofouling. A custom chamber was designed (details in part 4.5.2 of the Detailed Methods) to check and compare the resistance against formation of calcium carbonate scaling and bacterial (S. aureus) adhesion under dynamic conditions (velocity = 0.06 m / s and wall shear stress = 8.5 mPa). For antifouling, the surfaces 008864365

[0218] 27 were placed in the middle of chamber under continuous flow of water containing scaling precursor, 1 mM of CaCl2 and 2 mM of NaHCOs (supersaturated conditions) for 96 hrs. After that the surfaces were rinsed with water and analysed for crystal growth using SEM and energy-dispersive X-ray spectroscopy (EDS) (Fig. 53). F-UiO-66 / Fomblin SLIPS performed exceptionally well, showing almost no crystal growth (<4%) and maintaining 0Adv = ~1 19° and A0 = 8°, whereas large crystals of CaCOs were clearly visible on the control samples (Fig. 53). The superhydrophobicity of commercial NeverWet® coating was lost with 0Adv changing from -152° to -70°. The total surface coverage with scaling the exemplary SLIPS, AI / Si500 and NeverWet® was recorded <4%, -81 %, and -53%, respectively. For anti-biofouling, surfaces were exposed to continuous flow of dense S. aureus culture (OD600 = 0.3). The bacterial adhesion and biofilm formation were assessed after 6 hrs and 50 hrs, respectively. The surface coverages were quantified using SEM (Figs. 54 and 55). Bacteria colonies were clearly visible on control samples, whereas none was observed on the exemplified SLIPS after 6 hrs. After 50 hrs, a thick biofilm formed on the AI / Si500 control; a biofilm was also visible on the other two controls, PTFE plate and NeverWet® coating, but was less dense (Fig. 5). Few bacteria were spotted on SLIPS; the quantitative data of the surface coverage is presented in Fig. 56. The exemplified SLIPS showed <1 % of coverage (with discrete cells) even after 50 hrs. This testing indicates that SLIPS made according to the present disclosure have anti-fouling and antibiofouling properties. Overall, the obtained performance demonstrates the value of a rational approach to SLIPS design and should widen the breadth of practical applications for SLIPS and liquid repellent surfaces in general.

[0219] Brief Methods

[0220] Sample preparation Either water-based green approach (for NH2-UiO-66 and NH2-UiO-67) or solvothermal technique (for UiO-66, UiO-67, ZIF-8 and MOF-5) were used to synthesize the various MOF particles42 44. Specific and detailed synthesis procedure for each MOF types is presented in part 3 of the Detailed Methods.

[0221] Briefly, in water-based approach, sodium salt of organic linkers (2-aminoterephthalic acid and 2-amino-4 4'-biphenyldicarboxylic acid) and metal salts (ZrOCL'SFLO) were solubilized in water and mixed slowly, forming MOF precipitates. After stirring for 12 hrs at room temperature, MOF crystals were centrifuged and washed 3 times with DI water to remove unreacted linker and sodium salt from the pores. The water remained trapped in the pores was removed following the Soxhlet method in ethanol for 16 hrs at 120 °C. The resulting crystalline powder was dried under vacuum for 12 hrs at 100 °C.

[0222] In solvothermal synthesis, specified amounts (typically 50 mM) of organic linkers (terephthalic acid or 4 4'- biphenyldicarboxylic terephthalic acid) and metal salts (ZrOCL'SFW and Zn (NO3)2'6H2O) were dissolved in dimethyl formamide (DMF) and reaction mixture was kept 12 hrs at 120 °C. The obtained MOF particles were washed twice with DMF, acetone and chloroform to remove unreacted chemicals. The resulting crystalline powder was dried 12 hrs under vacuum at 100 °C. 008864365

[0223] 28

[0224] Post ic modification of MO Fs. To alter the MOF pore chemistry octanoic acid (OA) and heptafluoro-butyric acid (HBA) were linked to NH2 group presented on the MOF linker. Dried MOF powder or substrate with L / L MOFs were dispersed / immersed in DMF containing one equivalent of OA and HBA to organic linker. Then, the solution was stirred / kept at 80 °C for 12 hrs. Following this, the particles / surfaces were washed twice with DMF and acetone, and three times with chloroform before drying under vacuum for 12 hrs at 100 °C. MOF particles dispersion in acetone was sprayed onto the cleaned metal / glass substrates using a spray gun. Briefly, 10 mg / mL of MOF particles were dispersed in acetone and then sonicated for 30 minutes to get a homogeneous suspension. The weight of each substrate was recorded to monitor the amount of deposited MOF. The suspension was sprayed with a commercial spray gun (Iwata Eclipse, ECL2000) using a nitrogen gas pressure of 2.5 bar as controlled from a nitrogen cylinder fitted with a controller and pressure gauge. The samples were dried for 12 hrs under vacuum at 100 °C. of MOFs. Following the self-assembly of organic linker, the substrate was then immersed in 25 mM DMF solution of metal salt for 20 minutes at 120 °C followed by washing (which included 1 -minute sonication) and immersion in linker solution for another 20 minutes23. This completed one cycle of MOF growth. More than 20 cycles were needed in total to achieve a relatively thick and uniform MOF coating (Fig. 7). Finally, the surface was thoroughly washed by sonicating in DMF and then chloroform to remove metallic or linker aggregates. The surface was vacuum dried for 12 hrs at 100 °C.

[0225] SL / PS fabrication. Sprayed or L / L MOF (see part 3.7 of the Detailed Methods) surfaces were weighed and infused with excess amount (~20 times of the MOF weight) of lubricant onto the horizontally placed surface maintained at 100 °C on hot plate covered with glass Petri dish. After infusion for 12 hrs, the samples were kept tilted at 90° for one hour and then spun at 2,000 RPM to get rid of excessive lubricant for all standard tests except spinning test where surfaces were subjected to different spinning speeds ranging from 100 - 10,000 RPM. As a first control, aluminium substrates, cleaned in acetone, water and isopropyl alcohol (10 minutes each), were immersed in a bath of boiling deionized water for 10 minutes. After etching, the samples were rinsed with deionized water and dried with nitrogen. Excess of Si500 oil was infused in the rough structures following the same procedure described above (under heading “SL / PS fabrication”) for 12 hrs at 100 °C. The samples were tilted at 90° for one hour and then rotated at 2,000 RPM for one minute after cooled down to room temperature. As synthesised hydrophilic (NH2-UiO- 66) MOF nanoparticles, sprayed and infused with Si500 lubricant were also used as the second control to study the effect of pore chemistry.

[0226] Characterization and stability tests A bespoke setup consisting of an adjustable stage retort stand, a syringe pump, a light source and a zoom lens fitted to a CMOS camera was used for contact angle 008864365

[0227] 29 measurement45. Contact angle hysteresis (A0) was calculated as the difference of advancing (0Adv) and receding (0Rec) angles, which were measured by processing the recorded video with MATLAB. Water shedding setup comprised of a water reservoir (plastic 2 L water bag) connected via a flow controller to a syringe with 0.5 mm outlet diameter. The surfaces were placed at 45° tilt stage and the syringe tip height was kept 3 cm. Water droplets (~20 pL, ~4 mm diameter) dripped from the syringe onto the centre of the test surface. Two different rates, 50 mL / h and 100 mL / h, were used to assess the SLIPS stability herein. bespoke setup fitted with nitrogen gas cylinder connected to syringe (outlet diameter of

[0228] 2.5 mm) via electronic pressure valve was used to assess the impact resistance on SLIPS7-23. The maximum jet speed reached was ~35 m / s at 12 bar pressure and the time for each jet was ~25 ms. The surfaces placed at 30° tilt stage were impacted thrice at the same location and the process was recorded using high-speed camera (Phantom V411). After jet impact, the stability of surfaces was assessed by checking its slipperiness, followed SEM imaging to check mechanical erosion.

[0229] Ice adhesion measurement: A bench ■top icing chamber constructed using a heat-exchanger, a rotary aluminium stage (to mount samples) connected to a refrigeration unit (FP50-HL Refrigerated / Heating Circulator, Julabo) with bath fluids (H5, Julabo) was used for ice adhesion measurements2345. A stepper motor-controlled system with extension rod connected to a force gauge (M4-50, MARK-10) was used to push the frozen ice cuvettes at -25 °C. The system was operated using LABVIEW software to measure the adhesion forces.

[0230] Adhesion force measurement using AFM

[0231] Adhesion forces between MOF particles (NH2-UiO-66, A-UiO-66 and F-UiO-66) and lubricants (Si50 and Fomblin) were measured using a Bruker Multimode 8 atomic force microscope (AFM) with PeakForce Quantitative Nanomechanics (PFQNM) in ‘tapping mode’. Lubricant coated AFM tips (with 8 nm radii) were used as probes and MOF particles were adhered to piezo stage using double-side carbon tapes. Force distance curves were obtained at ~0.1 pm / s approach and retraction velocity at room temperature (20 - 25 °C). The ramp distance was 750 nm, and the maximum normal force applied on the mica surface was kept constant (750 nN) using a relative trigger threshold.

[0232] Detailed Methods

[0233] 1. Materials

[0234] Aluminium substrates (annealed, 0.5 mm thick, 99.99% trace metals basis) were purchased from Alfa Aesar. All chemicals including, zirconium oxychloride octahydrate (ZrOCh'SFLO), Zinc nitrate hexahydrate (Zn(NO3)2'6H2O), terephthalic acid, 2-methylimidazole, 2-amino terephthalic acid, heptafluorobutyric acid, octanoic acid, silicone oils (with 50 and 500 cSt viscosity, abbreviated as Si50 and Si500 in this paper), Fomblin. Krytox VPF 1525 (the fluorinated lubricants), dimethyl formamide 008864365

[0235] 30

[0236] (DMF), chloroform, acetone, isopropanol, calcium chloride (CaCh), acetic acid, sodium hydroxide (NaOH) and sodium bicarbonate (Na2HCO3) were purchased from Sigma Aldrich. 2-amino-44'- biphenyldicarboxylic acid was purchased from CD BioSciences Inc. USA. All chemicals were used without further purification. Deionized (DI) water with resistivity 18.2 MQ was used in all experiments.

[0237] 2. Characterisation instrumentation

[0238] Throughout this disclosure, all experimental values are determined using the following apparatus and protocols.

[0239] Surface morphologies of MOF nanoparticles and SLIPS were imaged using scanning electron microscopy (SEM) (EVO25, Carl Zeiss, Germany). For SEM, the specimens were immobilized on a metal stub with double-sided adhesive carbon tape and coated with a thin gold film, then observed at 10 kV voltage and 10 pA current. A JEOL 4700F dual beam system (Focused gallium ion beam coupled SEM) was used to measure the thickness of sprayed and surface-grown MOFs at 3 kV. The powder X-ray diffraction (PXRD) of the MOF powders were obtained using a Stoe STADI-P spectrometer at ambient temperature, with tube voltage of 40 kV, tube current of 40 mA in a stepwise scan mode (5° min1). Fourier-transform infrared spectroscopy (FTIR) spectra was recorded with a spectrophotometer (Spectrum Two™, Perkin Elmer) in the range of 400 to 4000 cm1.13C-nuclear magnetic resonance (NMR) spectra was obtained through a solid-state NMR using a Bruker Avance 300 spectrometer with 7.05 T wide-bore magnet at ambient probe temperature was used. High-resolution solid-state13C spectra were recorded at 75.5 MHz using a standard Bruker 4 mm double-resonance magic-angle spinning (MAS) probe. Solid materials were packed into zirconia rotors of 4 mm external diameter and spun at the MAS frequency of 12 kHz. High-resolution solid-state13C NMR spectra were recorded using cross-polarization (CP), MAS and high- power proton decoupling. Typical acquisition conditions for13C CPMAS total suppression of spinning sidebands (TOSS) spectra were: 1 H 90° pulse duration = 2.45 ps; contact time = 2 ms; recycle delay = 5 s.13C chemical shifts are presented relative to tetramethylsilane which was calibrated using glycine (176.46 ppm). Raman spectra were recorded on Bruker (SENTERRA II) at 785 nm wavelength, 50 mW laser power and 1.5 cm1resolution. Adhesion forces between MOFs and lubricants were measured using a Bruker Multimode 8 atomic force microscope (AFM) and the method details are presented in section 4.2.5. The transmittance of surfaces before and after lubricant infusion was measured using UV-Vis spectroscopy (UV-3600 iplus, Shimadzu) in a wavelength range of 200 nm to 800 nm. Transmission electron Microscopy (TEM) was performed at 200 kV on a JEOL JEM-2100 F system with a Schottky field emission gun. The samples were prepared by dispersing the MOF powder in ethanol and then casting onto a copper grid mesh and followed by solvent evaporation in air. The TEM images were taken using a Gatan Onevier Camera with full 4 k x 4 k resolution. The BET-surface area was recorded using a Quantachrome surface area and pore volume analyser (Anton Paar Nova Touch). The MOF pores were activated through removal of solvent traces by immersing in chloroform for 3 days followed by drying for 12 hrs under vacuum at 100 °C. In a typical experiment, the activated MOF samples (-200 mg) were 008864365

[0240] 31 loaded into the analyser, after degassing at 150 °C for 2 hrs. Then samples were cooled to liquid nitrogen temperature (77 K), before carrying out adsorption and desorption of N2.

[0241] 3. Methodology of Sample Preparation

[0242] 3.1. Synthesis of pristine UiO-66 and UiO-67 nanoparticles

[0243] Pristine UiO-66 and UiO-67 nanoparticles used in the intercalation (penetration of lubricants inside MOF architecture) studies were synthesised by solvothermal method. In case of UiO-66, terephthalic acid (0.41 g) and in case of UiO-67, 4 4'-biphenyldicarboxylic terephthalic acid (0.6 g) along with ZrOCI2-8H2O (0.8 g) were dissolved in 50 mL of DMF followed by heating for 12 hrs at 120 °C. The white precipitates were centrifuged and washed thrice with DMF and acetone and then dried for 12 hrs at 100 °C under vacuum before using them in different experiments.

[0244] 3.2. Synthesis of NH2-UiO-66 and NH2-UiO-67

[0245] A green method was adopted to produce the NH2-UiO-66 and NH2-UiO-67 nanoparticles46. Briefly, the sodium salt of organic linker 2-aminoterephthalic acid or 2-amino-4 4'-biphenyldicarboxylic terephthalic acid was obtained using 2 equivalents of NaOH in distilled water at 60 °C for 10 minutes with constant stirring. The mixture was then left to cool to room temperature. In the second step, ZrOCI2-8H2O was solubilized in DI water using 100 mM acetic acid. Both the above prepared solutions were mixed slowly, forming a yellow precipitate within 5 minutes. The mixture was then stirred for 12 hrs at room temperature. The obtained MOF crystals were centrifuged and washed 3 times with DI water to remove unreacted linker and sodium salt from the pores. Remaining water trapped in the pores was removed following the Soxhlet method in ethanol for 16 hrs at 120 °C. The resulting crystalline powder was dried for 12 hrs under vacuum at 100 °C.

[0246] 3.3. Synthesis of ZIF-8

[0247] Solvothermal method was used for ZIF-8 synthesis as well47. A mixture of Zn(NO3)26H2O (0.67 g) and 2- methylimidazole (0.167 g) in 50 mL of DMF was stirred until a clear solution was obtained. The solution was incubated at 140 °C for 24 hrs in hot air oven. The precipitates were filtered after cooling down the reaction mixture, washed thrice with DMF and acetone several times and kept in MeOH for 3 days and dried for 12 hrs under vacuum at 100 °C.

[0248] 3.4. Synthesis of NH2-MOF-5

[0249] NH2-MOF-5 was synthesised using solvothermal method adopted from previous published reports with some modifications48 49. No modulator has been used during synthesis. Zn(NO3)26H2O (1.2 g) and 2- aminoterephthalic acid (0.34 g) were dissolved in 40 mL DMF in a glass bottle. Then the solution was 008864365

[0250] 32 kept at 120 °C for 24 hrs. The reaction products were cooled to room temperature, and the precipitates were collected by centrifugation, washed twice with DMF and acetone and dried for 12 hrs under vacuum at 100 °C.

[0251] 3.5. Post-synthetic modification of MOFs

[0252] Pore chemistry of amino functionalised MOFs (NH2-UiO-66, NH2-UiO-67 and NH2-MOF-5) was modified through a simple post-synthesis procedure. Octanoic acid (OA) and heptafluoro-butyric acid (HBA) were used to produce alkyl and fluoro functionalisation, respectively. For each case, the dried MOF powder was dispersed in DMF and 1 equivalent of OA and HBA to organic linkers (2-amino terephthalic acid and 2-amino-4 4'-biphenyldicarboxylic acid) was added to the solution and stirred for 12 hrs at 80 °C. Following this, crystals were centrifuged and washed twice with DMF and acetone, and three times with chloroform before drying under vacuum at 100 °C. Only alkyl functionalisation was performed on NH2- UiO-67 and NH2-MOF-5.

[0253] 3.6. Particle spraying

[0254] The synthesized MOF particles were characterized for their morphology, chemical structure and crystallinity using SEM, FTIR and PXRD, respectively (Figs. 23, 4, 5 and 6). Following that, particles were sprayed on metallic aluminium and glass coupons of various sizes followed by oil infusion to create the corresponding SLIPS. The substrates were sonicated for 15 minutes each in acetone, water and isopropyl alcohol to clean them before spraying. MOF particles dispersion in acetone was sprayed onto the substrates using a spray gun. Operation parameters (such as sonication time for uniform dispersion of MOFs in acetone, spraying pressure, nozzle size, MOF dilution, etc.) were tuned to obtain uniform MOF nanoparticle layer on substrates (Fig. 7A). Briefly, 10 mg / mL of MOF particles were dispersed in acetone and then sonicated for 30 minutes to get a homogeneous suspension. The suspension was sprayed with a commercial spray gun (Iwata Eclipse, ECL2000) using a nitrogen gas pressure of 2.5 bar as controlled from a nitrogen cylinder fitted with a controller and pressure gauge. Approximately equal number of coatings were sprayed (15-17 spray passes) onto each surface to obtain thickness of ~10 pm. Acetone was then removed from MOF pores by drying the samples for 12 hrs under vacuum at 100 °C. The weight of each substrate was recorded to monitor the amount of deposited MOF.

[0255] 3.7. Layer-by-layer growth of MOFs

[0256] The surface-grown MOFs were obtained using a layer-by-layer (L / L) growth technique50. In an optimal cycle of L / L growth of MOF, the aluminium substrate was immersed in 100 mL of DMF solution of MOF linker (25 mM) in a tightly closed glass bottle for 4 hrs to get uniform self-assembly of linker at 120 °C. The substrate was then rinsed in DMF and immersed in 25 mM DMF solution of ZrCl2.8H2O for 20 minutes at 120 °C followed by washing (which included 1 -minute sonication) and immersion in linker 008864365

[0257] 33 solution for another 20 minutes. This completed one cycle of MOF growth. More than 20 cycles were needed in total to achieve a relatively thick and uniform MOF coating (Fig. 7B). Finally, the surface was thoroughly washed by sonicating in DMF and then chloroform to remove metal or linker aggregates. The surface was vacuum dried for 12 hrs at 100 °C. The surface grown MOFs were modified with alkyl and fluoro molecular chains as described above.

[0258] 3.8. SLIPS preparation

[0259] The surfaces with sprayed MOF particles were placed horizontally on the hot plate and infused with different lubricants (silicone or perfluorinated) for 12 hrs at 100 °C followed by cooling down to room temperature. The details of lubricants used are presented in Table 1 . After completing the infusion process, the samples were tilted at 90° for one hour and then rotated at 2000 RPM for one minute to get rid of the excessive lubricant. The surfaces were subsequently weighed again to obtain the final mass of lubricant infused (Table 2). The SLIPS were then subjected to various stability tests. SLIPS prepared from L / L grown MOFs followed the same infusion procedure. Thickness of the sprayed and L / L grown MOF layer was measured using FIB-SEM as presented in Fig. 8.

[0260] Table 1. The properties of lubricants used in this study. The data is obtained from online material safety data sheets (MSDS) available at Sigma Aldrich™. Same as above.

[0261] Table 2. The mass of lubricant (presented in terms of MOF weight) retained by different MOFs after tilting at 90° for one hour and spinning at 2000 RPM for one minute. 008864365

[0262] 34

[0263] 3.9. Control sample preparation

[0264] Boehmite surface was used as a control in some of the stability testing which include spinning, water shedding and jet impact. Uniform roughness (Fig. 19) was generated by reacting the metal substrate with water51. Briefly, as-received aluminium samples were thoroughly cleaned in acetone, water and isopropyl alcohol and then immersed in a bath of boiling deionized water (100 °C) for 10 minutes. After etching, the samples were rinsed with deionized water (15 minutes each) and dried with nitrogen. Next as described above, Si500 oil was infused in the rough structures for 12 hrs at 100 °C and then cooled down to room temperature. The samples were then tilted at 90° for one hour and then rotated at 2000 RPM for one minute to get rid of excessive lubricant.

[0265] 3.10. Contact angle measurement

[0266] A bespoke setup was used for the contact angle measurement50 52. The setup consists of an adjustable stage, retort stand, a syringe pump (World Precision Instruments, Aladdin single-syringe infusion pump), a light source (Thorlabs, OSL2) and a zoom lens (Thorlabs, MVL7000) fitted to a CMOS camera. Contact angle hysteresis (A0), employed as a criterion for assessing SLIPS slipperiness, was calculated from advancing (0Adv) and receding (0Rec) angles measured by processing the recorded video with MATLAB5052

[0267] 3.11 . Spinning stability test

[0268] Retention of lubricants by different MOFs was tested using a spinning stability test. The change in mass and A0 on substrates infused with excess of lubricant were measured before and after spinning.

[0269] Substrates were spun at 100, 500, 1000, 2000, 5000 and 10000 RPM for 1 minute. Change in A0 and loss in lubricant mass were plotted in Figs. 17 and 18.

[0270] 3.12. Water shedding test

[0271] The water droplet shedding test, considered to be a harsh test for oil retention capability of SLIPS, can drain the lubricant due to shear force and cloaking of the water droplet by the lubricant53. To carry out this test, a custom setup was used, which comprised a water reservoir (plastic, 2 L water bag) connected via a flow controller to a syringe. The syringe tip was kept at 3 cm height above the surface under test, which was inclined at 45° from the horizontal. Water droplets (~4 mm diameter) dripped from the syringe onto the test surface, at a cumulative volume flow rate of 150 mL / h for early shedding tests which were used to establish the rational choice for MOF pore size, lubricant choice and the corresponding pore chemistry (functionalisation). This created a continuous stream of drops impacting the surface at ~80 cm / s. The Weber number (We) and Reynolds number (Re) were calculated to be ~16 and -2500, respectively (We=pV2d / o and Re=Vd / v, where p denotes the liquid density, o denotes the liquid surface tension, v is the kinematic viscosity and V is the impact speed of droplets). The syringe volume (50 mL) was used as a measure of shedding cycle; A0 and lubricant mass loss were measured after different cycles. Following 008864365

[0272] 35 the initial triage, once the appropriate combinations of pore size / chemistry and MOF / lubricant combinations were determined (e.g. F-UiO-66 / Fomblin and A-UiO-67 / silicone oil), a cumulative flow rate of 100 mL / h was used for long-term shedding test. Change in A0 was recorded at pre-defined time intervals from 30 minutes to 50 hours for these tests. The obtained results from different water shedding assessments are listed in Table 3 and Table 4.

[0273] Table 3. Dynamic contact angles and water shedding stability of SLIPS prepared from UiO-66 against four different lubricants including Si50, Si500, Krytox and Fomblin. The water shedding cycles numbers represent the maximum duration sustained with A0 < 10°. Each cycle used 50 mL of DI water.

[0274] Table 4. Dynamic contact angles and water shedding stability of SLIPS prepared from UiO-66 / Fomblin and UiO-67 / Si500. The water shedding cycles numbers represent the maximum duration sustained with A0 < 10°. Each cycle used 50 mL of DI water.

[0275] 008864365

[0276] 36

[0277] Table 5. The effect of pore surface chemistry on the SLIPS durability. Wettability data of hydrophilic (NH2- UiO-66) and hydrophobic (A-UiO-66 and F-UiO-66) MOFs infused with four different lubricants, Si50, Si500, Krytox and Fomblin. Non-underlined and underlined values represent the failure and stability of the surfaces under water shedding, respectively. Stability benchmark used was >10 water shedding cycles and A0 <10°.

[0278] 4. Computation Studies and Sample Testing

[0279] 4.1. Molecular dynamics and experimental study on lubricant intercalation

[0280] 4.1.1. Capillary pressure in the MOF pores

[0281] The capillary pressure in the MOF pores (e.g. UiO-66) for silicone, Krytox and Fomblin lubricants were calculated using the Young-Laplace equation54,

[0282] Pcap =R. (Equation 1) where R is the radius of MOF aperture (~0.6 nm); 0 is the contact angle which represents the surface tension between MOF and the lubricant; and o is the interfacial tension at the interface. The capillary pressure in the MOF pore was -62 MPa for silicone oil (o = 18.8 mN / m), -60 MPa for Krytox (o = 18 mN / m) and -73 MPa for Fomblin (o = 22.0 mN / m).

[0283] 4.1.2. Molecular dynamics simulations

[0284] Molecular dynamics simulations were conducted with the Large-scale Atomic / Molecular Massively Parallel Simulator (LAMMPS)55to investigate the intercalation of lubricant chains inside MOF pores. Molecular structures of NH2-UiO-66 and lubricants, silicone and Fomblin, were created using Gaussian View program (Figs. 57A-57C). The molecular structure of MOF comprised of tetrahedral pores with four metal clusters occupied by related organic linkers. The chain lengths for both the lubricants, silicone ([Si- 0-(CH3)2]2O) and Fombilin (CF3O(C3F6O2)5(CF2O)5CF3) were chosen to be similar. It is important to note that the sizes of the simulated molecular structures are smaller than the actual molecules due to the computational limits.

[0285] The flexible UFF force field was employed and LAMMPS input files were created using the lammps_interface program56. The molecular structures were optimized using PM7 method and their atomic charges were calculated using the Merz-Kollman electrostatic potential (ESP) charge method in 008864365

[0286] 37 the Gaussian program57. Periodic boundary conditions were applied with a 50 A square box. The cut-off for van der Waals and Coulombic interactions were set 12.5 A. A time step of 0.5 fs was used for the whole simulation. The particle-particle particle-mesh (pppm) simulation was used to calculate the long- range electrostatic interactions, with a relative precision of 104(dimensionless). Each run was equilibrated for 0.6 ns at 300 K in the canonical (NVT) ensemble using the Nose-Hoover thermostat58 59. The change in potential energy for all runs was less than 0.5% during equilibration (between 0.5 ns and 0.6 ns). At the beginning of the MD simulation, the MOF and lubricants were all separated. Following equilibration, two Fomblin chains were adsorbed on a single MOF particle (Fig. 9A). In contrast, the silicone chains were partially separated from MOF (Fig. 9B). It was also observed that the Fomblin chain could enter and perfectly fits into the octahedral MOF pore whereas silicone chain failed to penetrate through the aperture. The penetration of Fomblin chain inside the MOF pore (~6 A) could be justified by its smaller diameter (-2.76 A) in comparison to the larger diameter (-5.92 A) of silicon molecular chain. The diameters of lubricant chains were calculated using PM7 method. However, given the bigger aperture size of UiO-67 (8 A), silicone chain could be able to enter comfortably inside its pore (Fig. 11 and Fig. 24).

[0287] 4.1.3. Samples preparation to study lubricant intercalation

[0288] Pore size dependent intercalation of lubricant into the MOFs was confirmed experimentally. Two types of MOFs, namely, 1 g of UiO-66 and UiO-67 powders were infused with 2 g of Si500 in a 15 mL falcon tube. After infusion, the samples were kept for 12 hrs at 100 °C to replicate the SLIPS fabrication procedure. Samples were then cooled down to room temperature and then washed extensively (three times each) with chloroform and hexane to remove physically adsorbed lubricant. Washed samples were dried for 12 hrs under vacuum at 100 °C and then the dried powders were subjected to BET surface area characterization,13C-NMR and Raman spectroscopy to confirm the presence and intercalation of silicone chains inside MOFs.

[0289] 4.2. Pore chemistry and host-guest interactions

[0290] 4.2.1. Surface energy for different functional groups

[0291] The Lifshitz-van der Waals / acid-base (LW / AB) method can determine the surface energy of solids60. The surface energy can be divided into three components, y = yLW+ 2^ / Y+Y-, (Equation 2) where yLW, Y+and Y~ denote the Lifshitz-van der Waals component, acid component and base component, respectively. The relationship between solid and liquid is (Equation 3) where 0 is the contact angle between solid and test liquid, and the subscripts S and L denote solid and liquid, respectively. The surface energy can be calculated by measuring the contact angles of three test liquids (with different yLW, Y+and y-)- 008864365

[0292] 38

[0293] To compare the wetting and adhesion between different functional groups (used in MOF functionalisation) and liquids (water and lubricants), the surface energy was measured quantitatively using the LW / AB method. The test liquids used in this experiment were water, diiodomethane and ethylene glycol. The obtained surface energy parameters are shown in Table 661. By solving a set of three simultaneous equations, surface energy of solid (silica wafer) modified with three different functional groups was calculated (Table 7).

[0294] Table 6. Surface energy parameters (mJ rrr2) of the testing liquids at 20 °C.

[0295] Table 7. Contact angles of three functionalized surfaces and their calculated surface energies.

[0296] 4.2.2. Noncovalent interactions using density functional theory (DFT)

[0297] To study noncovalent interactions between different MOF linkers and lubricants, as a first step, the molecular structure optimisation was done using DFT at B3LYP / 6-311G basis set in the Gaussian 16 software and confirmed by frequency analysis in the absence of imaginary frequencies. The results were then used to calculate the reduced density gradient (RDG) function62using the Multiwfn program63and plotted using VMD software64. The RDG function is based on the electron density (p) and its derivatives (sign(A2)p). Sign(A2) denotes the sign of the second eigenvalue (A2) of the electron-density Hessian matrix, which is used to distinguish the attractive and repulsive interactions.

[0298] Noncovalent interactions were characterized by low density and reduced gradient values (Fig. 27). The orange isosurfaces represent strong mutual exclusion (repulsion) and nonbonded overlaps. The green discs represent van der Waals (vdW) interactions. Isosurfaces appear between Fomblin chain and hydrophobic linkers (functionalised with alkyl and fluoro chains) suggesting strong vdW interactions. 008864365

[0299] 39

[0300] 4.2.3. Electrostatic potential analysis

[0301] Electrostatic interactions are different from the vdW interactions65 66. Hence, it is necessary to distinguish between electrostatic and vdW interactions separately. The electrostatic interaction might be able to control molecular orientation in the lubricant.

[0302] Isopotential surfaces of electrostatic potential (ESP) were also analysed using the Multiwfn program63and plotted in VMD software64(Fig. 27). Both, silicone and Fomblin chains showed weak electropositive behaviour. The amino, alkyl and fluoro functional groups showed electropositive, electroneutral and electronegative behaviours, respectively. The carboxyl groups and the amide bonds in the organic linkers were also found to be electronegative. The strong electrostatic interactions were observed between Fomblin and fluoro functionalised linkers (Fig. 27F). Silicone chains were observed to have electrostatic interactions with carboxyl functional groups and amide bond presented in functionalised linkers (Fig. 27B).

[0303] 4.2.4. Interaction energy decomposition

[0304] Symmetry-adapted perturbation theory (SAPT)67, implemented in PSI4 code68, was used to identify the relative contributions of electrostatic, dispersion, induction and exchange forces. The latter two forces belong to van der Waals interactions. The bronze standard method (sSAPTO / jun-cc-pVDZ) was employed to calculate the intermolecular interaction energies between the linkers and lubricants. The relative contributions of different interaction energies are shown in Fig. 28.

[0305] 4.2.5 Adhesion force measurements using atomic force microscopy

[0306] Adhesion forces between different MOF particles (NH2-UiO-66, A-UiO-66 and F-UiO-66) and the lubricants (Si50 and Fomblin) were investigated using a Bruker Multimode 8 atomic force microscope (AFM) with PeakForce Quantitative Nanomechanics (PFQNM) in ‘tapping mode’. Fig. 29 shows a schematic of the AFM set-up used. Bruker RTESPA-525 AFM cantilevers with 8 nm tip radii were used. Spring constant of the cantilevers were estimated using thermal noise method for calibration69. First, a thin layer of lubricant was adsorbed to the AFM tip by approaching a small quantity of lubricant dispensed on mica substrate. A cantilever without lubricant layer was used as a control. Next, MOF particles were adhered to piezo scanner using double-side carbon tapes and the unbounded or loosely attached particles were removed by blowing with pipette bulb. All AFM experiments were performed at room temperature (20 - 25 °C).

[0307] To exclude the possible capillary rise / imbibition into the MOF pores, the excessive lubricant presented on AFM tip was removed by adsorption on separate MOF particles until the adhesion forces became constant. The time for each MOF absorption event was kept higher than the capillary imbibition time, which was estimated using modified Washburn’s equation70as follows (Equation 4) 008864365

[0308] 40 where tb, L, and R are the capillary imbibition time, length of capillary tube and radius, respectively. L and R were estimated based on the typical UiO-66 nanoparticle (200 nm) and pore size (~1 nm), respectively. The symbols ., y and 0 denote dynamic viscosity, surface tension of the lubricant and the contact angle between the penetrating liquid and the solid, respectively. For Si50 oil, dynamic viscosity and surface tension are around 48 mN s / m2and 20 mN / m, respectively. The anomalous coefficient of nanotubes Ki is around 0.5 when R is 1 nm70. Therefore, the imbibition time for the lubricant infiltrating a MOF particle was estimate as 0.4 ms. By ensuring that the contact time between MOF particle and tip exceeded the calculated imbibition time, i.e. 0.4 ms, after multiple contacts with dry MOF nanoparticles, it was ensured that ultimately only a thin layer of lubricant was left on the AFM tips, which is held together by van der Waals interactions between the tip and the oil. This allowed us to assess the interaction between the lubricant and MOF particle without any lubricant in its pores. The approach is similar to previously published studies on the measurement of adhesion forces between solid-liquid using AFM71 72. The adhesion forces between bare AFM tip (without lubricant) and MOF particles were also measured for comparison.

[0309] Representative force-distance curves for Fomblin against NH2-UiO-66 and A-UiO-66 are shown in Fig. 30. Tip approach velocity and retraction velocity were kept at ~0.1 pm / s during all the measurements. The ramp distance was 750 nm, and the maximum normal force applied on the mica surface was kept constant (750 nN) using a relative trigger threshold. Neither the ramp distance nor the maximum applied force were considered independent variables. The presented adhesion forces in Fig. 31 are the average pull-off force measured from 8 individual force-distance curves.

[0310] Force-distance curves were analysed using Bruker NanoScope Analysis 9.1 software. Briefly, the adhesion force was calculated as the difference between the baseline (0 mN / m force) of the retract dataset and the largest negative value (pull-off point). Adhesion forces from each tip-MOF combination were averaged, and the standard deviation was calculated. Adhesion forces were normalised by 2TTR, where R is the tip radius. Forces are expressed in units of tension per unit length (N / m) which is equivalent, numerically and dimensionally, to the interaction free energy (J / m2).

[0311] As shown in Fig. 31 , adhesion forces decrease in the order F-UiO-66 / Si50 > A-UiO-66 / Si50 > A-UiO- 66 / Fomblin > F-UiO-66 / Fomblin > NH2-UiO-66 / Si50 > NH2-UiO-66 / Fomblin. It is important to note that there might be some contribution of hydrodynamic and capillary forces in the measured adhesion values. But at the used low tip velocity of 0.1 pm / s, the contribution of hydrodynamic forces expected to be negligible73 74. Despite the removal of excessive lubricant from AFM tips through multiple adsorption on bare MOF particles, there might be some capillary forces presented. Overall, the adhesion forces Fad consist of the electrostatic force Feiec, the van der Waals force Fvdw, and the capillary force Fcap in the presence of lubricant meniscus75:

[0312] Fad — Fejec+ FVC[ V + Fcap, (Equation 5)

[0313] The capillary force Fcap between tip with radius R and a MOF particle can be calculated using:

[0314] Fcap=4TTR cos0 y, (Equation 6) 008864365

[0315] 41

[0316] For silicone oil, the maximum value of Fcapis calculated around 2 nN and its normalised value (2TTR) is 0.04 N / m. This value is equivalent to the adhesion forces measured between hydrophilic NH2-UiO-66 and silicone oil using AFM (-0.06 N / m) suggesting that the other interactions (Felecand Fvdw) are negligible. However, the adhesion forces measured for silicone oil and hydrophobic MOFs using AFM were much larger, >3 N / m and can be interpreted as non-covalent interactions with negligible contribution of capillary and hydrodynamic forces.

[0317] 4.3. Lubricant replenishment and retention

[0318] 4.3.1. Lubricant recovery

[0319] The reticulated porosity of MOFs enables local recovery / replenishment of lubricant from neighbouring MOF pores. The lubricant replenishment / recovery of SLIPS was thus studied alongside water shedding tests. For SLIPS with sprayed nanoparticles, the inter-particle gaps can also serve as source of lubricant replenishment (see Fig. 33). The bright, yellow spot enabled the presence or absence of lubricant to be discerned readily. Fig. 33 shows the snapshots from videos of the top-view of SLIPS recorded using a high-resolution camera. The boundary of the bare MOF surface (covering the path of the sliding droplets) can be easily distinguished from the lubricant-coated surface. Lubricant recovery over time was carefully assessed from these videos.

[0320] 4.3.2. Theoretical loading capacity of UiO-66

[0321] Theoretical loading capacity (LF) of UiO-66 (0.72 g / g) for Fomblin was estimated by assuming that the volume occupancy of lubricant molecules inside MOF pores is similar to that of small molecules,

[0322] LF = VMOFPF (Equation 7) where the specific volume (VMOF) of UiO-66 pore76is 0.379 cm3g-1and the density (pF) of Fomblin is 1 .9 g mL-1.

[0323] 4.4. Robustness tests

[0324] 4.4.1 . Comparison against state-of-the-art SLIPS

[0325] The duration of lubricant retention on the surface and the maximum dispensed liquid (water) volume were benchmarked (see Fig. 43) and compared the results using SLIPS described herein against control SLIPS. A0 <10° for water droplets was used as a metric to assess the retention of surface liquid repellence (slipperiness) over time.

[0326] To the best of the knowledge of the inventors, only handful of studies have assessed / reported similar durability studies on SLIPS under continuous water shedding and most of the surfaces are unable to survive for more than couple of hours. The volume of water droplets used in previous studies ranged from 008864365

[0327] 42 around 10 pL to 20 pL, and the test surface inclination angle ranged from 7° to 30°. A droplet dripping frequency of 1 s1was assumed in order to compare the duration data of the above studies with the present results. Each data point in Fig. 43 shows the stability of different combinations of surfaces and lubricants during continuous water shedding experiments:

[0328] • Electrosprayed rubber: Vulcanized silicone rubber prepared using a one-step electrospray method infiltrated with a perfluoropolyether lubricant77,

[0329] • ZnO nanowire: Zinc oxide nanowire arrays prepared by a chemical bath deposition (CBD) and infused with silicone oil78,

[0330] • CuO nanoparticles: Needle-like copper oxide nanoparticles (synthesized using CBD method) coated with polymethylsiloxane (PDMS) and infused with silicone oil79,

[0331] • Si nanotubes: Silicon nanotube array fabricated by spacer defined intrinsic multiple patterning with lubricant Krytox 152580,

[0332] • Fluoro PDA: Polydopamine (PDA) layer grafted with the fluorinated poly(hexafluorobutyl methacrylate-co-glycidyl methacrylate) polymers and infused with perfluorinated lubricant81.

[0333] 4.4.2. Jet impact test

[0334] A bespoke set-up fitted with nitrogen gas cylinder connected to an electronic pressure valve was used for jet impact test52. Diameter of water jet was 2.5 mm and the maximum back-pressure was ~12 bar. The speed of jet was calculated from motion of the piston and related parameters including nozzle diameter using following the continuity equation:

[0335] •nd2Ah / 4 = TTd„VjetAt / 4 (Equation 8) where At is the elapsed time, Ah is the distance, dsis the cylinder diameter, dnthe nozzle (jet) diameter and Vjet is the jet speed.

[0336] The maximum jet speed reached in these experiments (~35 m / s) was determined by averaging the maximum speeds in different tests. The corresponding liquid Weber number (I / e / =pV2dn / y) calculated for the 2.5-mm jet was -42,500. The surface showed no signs of damage or permanent liquid impalement even after at least 3 jet impacts on the same spot. The liquid impalement resistance of surfaces was assessed using a droplet mobility test; a droplet was placed at the centre of the impact location following jet (Figs. 47 and 48) and checked for pinning or sliding.

[0337] 4.5. Applications

[0338] 4.5.1. Ice adhesion measurement

[0339] A custom bench-top icing chamber was used for the ice adhesion experiments as reported in the inventors’ previously published work50 82. The chamber comprised of a transparent, double-walled container and a cooling base with external dimensions of 30 cm x 20 cm x 18 cm and a 10 mm air gap between its external and internal walls. The 5 mm walls were made of thermally insulating Perspex and the air gap was evacuated to improve the insulation. The base contains an aluminium frame, a base 008864365

[0340] 43 plate, a compact heat exchanger (P1805368, UK Exchangers), 4 axial fans below the heat exchanger (ARX CeraDyna Series, RS Components), a rotary aluminium stage, a plastic shaft and two Peltier cooling modules between the aluminium stage and the heat exchanger. 4 K-type thermocouples (HH506RA) were used to measure chamber temperature. Temperature was controlled using a refrigeration unit (FP50-HL Refrigerated / Heating Circulator, Julabo) with bath fluids (H5, Julabo) connected to the compact heat exchanger. A 3-pin humidity sensor (HIH-4000-001 , RS Components) was used to measure humidity. The data acquisition system (DAQ) included a compact DAQ chassis (cDAQ-9174, National Instruments) with a temperature module (NI9213), a voltage module (NI-9263) and an analogue module (NI-9209). An extension rod connected to a force gauge (M4-50, MARK-10) was mounted on a custom-made driving system equipped with a stepper motor (17HS19-2004S1). LABVIEW software was used to operate and record the forces and determine the corresponding adhesion presented in Figs. 50-52.

[0341] 4.5.2. Dynamic anti-fouling and anti-biofouling tests

[0342] Flow chamber design: A closed-loop flow chamber with dimensions of 255 mm x 205 mm x 205 mm (w x h x d) was 3D printed from polylactic acid (PLA) polymer (Fig. 58) using PLA based melted extrusion modelling (Tiertime). The nozzle diameter for printing was 1 .75 mm and the geometry of chamber was developed on Autodesk Fusion 360 software. Inlet and outlet diameters were 20 mm. The chamber was connected to submersible pump (BARST, 350 L / h) and used for dynamic anti-fouling and anti-biofouling tests as explained below.

[0343] Anti-fouling: The fouling experiments were performed at dynamic conditions at 25 °C for 4 days (96 hr). A supersaturated solution of CaCh (0.222 g, 1 mM) and Na2HCO3 (0.336 g, 2 mM) in 2 L of DI water was stirred for around 60 minutes to obtain a clear solution. Then the surfaces were fixed in vertical position along the chamber wall using commercial Blu Tac® adhesive. A submersible pump was used to drive the supersaturated solution of CaCh and Na2HCO3 in a closed loop through the chamber at a flow rate of 350 L / h. Then the surfaces were characterised for crystal deposition / growth after 96 hrs using SEM with Energy Dispersive Spectroscopy (EDS). The obtained high-resolution images were processed using imaged for crystal growth quantification.

[0344] Anti-biofouling: Gram positive S. aureus bacteria (8325-4 strain) was used for anti-biofouling testing at a dynamic flow condition. A single colony was extracted from the glycerol stock of bacteria on LB agar plate (prepared using Lennox L Broth Base from Invitrogen™) and incubated for 12 hrs in 10 mL of LB broth at 37 °C to prepare primary culture. After growth, bacteria containing broth was diluted to OD600=0.3 which was measured with a UV-vis Spectrophotometer (Orion™ AquaMate). 500 mL of bacterial culture flowed through the chamber containing control and SLIPS and the temperature was maintained at 37 °C in the incubator. The flow rate was 350 L / h and wall shear stress was calculated as 0.0085 Pa. Bacteria adhesion and biofilm behaviours were checked (after 6 hrs and 50 hrs) under flow condition simulating urinary catheters. The culture inside chamber was refreshed every 6 hrs to maintain the bacteria concentration level and avoid overloading. SEM (EVO, ZEISS) with voltage 5 kV and current 100 pA was 008864365

[0345] 44 used to image samples after air-drying for 1 hr. The high-resolution SEM images were processed in Imaged software to quantitatively analyse the surface coverage with bacteria at five random locations.

[0346] Wall shear stress in chamber: For real-world applications such as urinary catheters83and heat exchanger tubes84, liquid containing contaminants, microbes or minerals flow across the surfaces, providing continuous shear that may also deteriorate the SLIPS or the retaining micro / nanoporous substrate structure. To evaluate the exemplified SLIPS, a closed-loop chamber was designed to test the surfaces under dynamic / flow of conditions. The flow Reynolds number was calculated by (Equation 9) where average velocity of flow V is 0.06 m / s, width of the chamber L is 0.04 m. Density of LB broth or supersaturated solution of minerals p is around 1000 kg / m3.Viscosity of LB broth p is 7x104Pa s. This yields Re=3428, which suggests that the chamber flow should be transitional.

[0347] To a first approximation, the Darcy-Weisbach equation is used, to estimate the mean wall shear stress T inside the chamber channel85:

[0348] T = p(V)2. (Equation 10)

[0349] The T inside chamber under maximum flow rate (350 L / h) is calculated 8.5 mPa which is comparable to wall shear stresses in medical catheters83.

[0350] References

[0351] A number of publications are cited above in order to more fully describe and disclose the invention and the state of the art to which the invention pertains. Full citations for these references are provided below. The entirety of each of these references is incorporated herein.

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Claims

00886436551Claims:1 . A surface coating comprising a reticulated structure that is a metal-organic framework having pores or a covalent organic framework having pores, and a lubricant comprising lubricant molecules, wherein the lubricant molecules are held within the pores of the reticulated structure and extend from the pore apertures thereof.

2. The surface coating of claim 1 , wherein the section of the lubricant molecules held within the pores of the reticulated structure have a maximum chain diameter that is no less than 10% of the diameter of the pore apertures.

3. The surface coating of claim 1 or claim 2, wherein the reticulated structure comprises a functional group that is complementary to the lubricant molecules.

4. The surface coating of claim 3, wherein the functional group of the reticulated structure is aprotic.

5. The surface coating of any one of claims 1 to 4, wherein the lubricant molecules comprise a functional group that is complementary to the reticulated structure.

6. The surface coating of claim 5, wherein the functional group of the lubricant molecules is aprotic.

7. The surface coating of any one of claims 1 to 6, wherein the lubricant has a kinematic viscosity in the range of 10-1000 cSt when measured at a temperature of 25°C.

8. The surface coating of any one of claims 1 to 7, wherein the pore apertures of the reticulated structure have a diameter within the range of 1 to 20 A.

9. The surface coating of any one of claims 1 to 8, wherein the reticulated structure is a metal-organic framework having pores.

10. The surface coating of any one of claims 1 to 8, wherein the reticulated structure is a covalent organic framework having pores.

11. A substrate comprising the surface coating of any one of claims 1 to 10.

12. A method of preparing the substrate of claim 11 , comprising the step of providing the reticulated structure on a surface of the substrate and subsequently infusing the reticulated structure with the lubricant.

13. A kit, comprising a reticulated structure that is a metal-organic framework having pores or a covalent organic framework having pores, and a lubricant comprising lubricant molecules, wherein the00886436552 lubricant molecules comprise a section capable of being held within a pore of the reticulated structure, whilst an adjacent section extends from a pore aperture thereof.

Images