EP2084252A1

EP2084252A1 - Ultra-thin hydrophobic and oleophobic layer, its method of manufacture and use in clockmaking as an epilame

Info

Publication number: EP2084252A1
Application number: EP07816284A
Authority: EP
Inventors: Samuele Tosatti; Stefan Zürcher
Original assignee: Rolex SA
Current assignee: Rolex SA
Priority date: 2006-12-01
Filing date: 2007-11-29
Publication date: 2009-08-05
Anticipated expiration: 2027-11-29
Also published as: US20100075138A1; EP1927648A1; EP2084253B1; JP2010511099A; EP2084252B1; WO2008064511A1; EP2084253A1; WO2008064510A1; US20100068553A1; CN101611124A; JP5385788B2; CN101611124B

Abstract

The invention relates to a new ultra-thin hydrophobic and oleophobic layer formed by self-assembly on a surface of a solid substrate having compounds of the general formula A-B in which A is a group having the formula (I) in which Z is C or N+; X is C-H or C-L, wherein L is an electroattractive group chosen from F, Cl, Br, I, CF3, NO2 and N(CH3)3+; Y is H or CH3, or Y, together with X, forms a heterocycle of 5 or 6 atoms; T is NH, CO, CONH or NH2+U-, wherein U- is a soluble anion, such as F-, Cl-, Br-, I, OH-, NO3-, HSO4-, SO42-, CO32-, HCO3- or SCN- for example, and B is a C1-C20 aliphatic linear alkyl group replaced partially or completely by F. The invention also relates to a method for preparing said layer and its use as an epilame.

Description

HYDROPHOBIC AND OLEOPHOBIC ULTRA-THIN LAYER, METHOD OF MANUFACTURE AND USE IN WATCHMAKING AS EPILAM.

The present invention relates to a new ultra-thin hydrophobic and oleophobic layer formed by self-assembly on a solid substrate surface of catechol foot compounds, a process for preparing this ultra-thin layer and the use thereof as an epilame.

The proper functioning of a watch movement depends, among other things, on its lubrication. The durability of the lubricant depends in particular on its maintenance in the operating zone: every watchmaker, however, has noticed that a drop of lubricant spreads rapidly over a clean part. The deposition of an epilame layer, generally in the form of a hydrophobic and oleophobic invisible molecular layer, avoids the spreading of the lubricant and its components.

The spreading of a liquid depends on the interaction forces between the liquid, the surface and the surrounding air (see JC Berg, "Wettability", Marcel Dekker, New York, 1993 and AW Adamson, "Physical Chemistry of Surfaces". ", Wiley). The parameter that characterizes the interaction forces between a liquid and the air is the surface tension, γ _LV . A surface energy γ _{sv is} similarly defined between a solid and the surrounding air and a parameter γ _L s between the solid and the liquid. For a drop of equilibrium liquid on a surface, the Young equation states that γ _S v ~ Y _LS = Y _L V'COSΘ, where θ is the contact angle of the drop of liquid with respect to the area. The Young equation also shows that if the surface tension of the liquid is lower than the surface energy, the contact angle is zero and the liquid wets the surface. This is what happens for a lubricant deposited on a clean metal surface: in In fact, a lubricant has a surface tension of 35-40 mN / m, whereas a common metal surface has a higher surface energy.

The surface energy depends on several factors (JP Renaud and P. Dinichert, 1956, "Surface states and spreading of clockwork oils", Bulletin SSC III page 681): the chemical composition and the crystallographic structure of the solid, and in particular of its surface, the geometrical characteristics of the surface and its roughness (and thus the defects and / or the polishing state), the presence of molecules adsorbed physically or chemically bonded to the surface, which can easily mask the solid and significantly change its surface energy.

Surface energy is often determined by the last atomic or molecular layer. The chemical nature of the solid is of little importance in relation to the state of its surface and the contamination that covers it. On a clean metal surface free of organic contamination, the contact angle in advance with a drop of water is less than 10 °. With a molecule forming self-assembled monomolecular layers (SAM: SeIf-

Assembled Monolayers) showing a -OH functional group

(eg HOC ₁₁ H ₂₂ SH), this contact angle is about 30 °, whereas it is about 110 ° for a -CH ₃ functional group (eg C ₁₂ H ₂₅ SH ) and about 118 ° for a -CF ₃ functional group (eg, C ₁₀ F ₁₇ H ₄ SH).

The manufacturing techniques used in watchmaking left until the 1930s a surface condition minimizing the spread of lubricants by the presence of a film lowering surface energy (M. Osowiecki, 1957, "A new wash-resistant epilame", Bulletin SSC III, page 735). This film disappeared with the improvements made to the washing techniques, causing the lubricants to spread more or less rapidly. In 1930, P. Woog of the Compagnie Française de Raffinage developed an anti-migration product based on stearic acid which he named "epilame". It was used in various branches of the industry until the end of the 60s. The name remained and designates in watchmaking any product used to guarantee the resistance of lubricants on a surface.

Deposition of a compound on a functional surface to lower surface energy and control wettability and adhesion is a fairly common process. However, its application as a barrier or antimigration film is limited to watchmaking (M. Massin, "Epilames and associated lubricants with high stability: properties, application technology and results in watchmaking", Proceedings of the Congress of Franco- German Chronometry, page 85, 1970, and "Design of lubrication in micromechanics: new achievements by preparation of surfaces associated with silicone fluids", Proceedings of the Congress of German and French Chronometry Societies, page 95, 1971), to the space industry ( M. Marchetti, "Global and Local Aspects of the Implementation of Fluid Lubrication in the Space Environment", INSA Doctoral Thesis, Lyon, 2000) and Electronics. The first two areas have in common the difficulty of replacing a used or exhausted lubricant.

Products based on stearic acid diluted in toluene were used in watchmaking until the 1970s (M. Osowiecki, reference above and P. Ducommun, 1956, "Synthetic clockwork oils", J. Switzerland Horl. Bij. 9-10, 117). Research undertaken in the late 1960s led to two important developments. On the one hand, a product based on silicone was developed (P. Massin, references above) but knew only limited success. On the other hand, products based on fluoropolymers were introduced in the course of the 1970s and are still used today.

Currently, the vast majority of epilams available on the market, such as Moebius' Fixodrop FK-BS, or the 3M Fluorad (FC-722 and others) line, consist of a fluorinated polymer dissolved in a perfluorinated solvent.

The deposition of the compound on the substrate is carried out by soaking it in a solution of perfluorinated solvent loaded with polymer. The solvent used is generally tetradecafluorohexane (CeFi ₄ ) which, once volatilized, is a greenhouse gas since it remains stable for 3200 years in the air and has a greenhouse potential of 7400 equ. CO ₂ . It is an object of the invention to provide compounds useful as an epilame which can be attached to a solid substrate surface without the use of environmentally toxic fluorinated solvents.

These objects are achieved by the invention as defined in the attached set of claims.

The invention indeed proposes a novel ultra-thin hydrophobic and oleophobic layer formed by self-assembly on a solid substrate surface of catechol foot compounds, and a process for preparing this ultra-thin layer which uses a non-fluorinated solvent which is environmentally friendly. the environment, for example a mixture of water and 2-propanol. Thanks to the catechol foot of the compounds used, this ultra-thin layer is firmly fixed to the surface of the solid substrate. This ultra-thin layer has satisfactory properties for use as epilame, particularly a contact angle in advance with water and a spread of a drop of oil, quite comparable to those of the layer obtained from the reference product Fixodrop FK-BS. The invention thus makes an important contribution to the ecological preparation of epilames.

The catechol foot compounds have the general formula

A-B in which

A represents a group of formula

in which

Z represents C or N ⁺ , X represents CH or CL, L being an electron-withdrawing group chosen from F, Cl, Br, I, CF ₃ , NO ₂ and N (CH ₃ ) S ⁺ ,

Y represents H or CH ₃ , or Y forms with X a heterocycle of 5 or 6 atoms, T represents NH, NH-CO, NH-CO-NH or NH ₂ ⁺ U ^" , ϋ ^" being a soluble anion, such as by example F ^", ^Cl", Br ^~, I, OH ^", NO _^3", HSO ₄ ^", SO ₄ ^{2 ',} CO ₃ ^2-", HCO ₃ ^"or ^SCN", and

B represents a linear aliphatic alkyl group C _x -C ₂₀ substituted partially or completely by F. Group A is used in particular to allow attachment of compounds to the surface of the solid substrate with the catechol group and solubilizing the amphiphilic molecule in the AB soaking solution.

Group B gives the ultra-thin layer its hydrophobic and oleophobic properties. Preferably the group B is a linear aliphatic group perfluorinated in its terminal part, for example of formula (CH ₂ ) _n - (CF ₂ ) _m CF ₃ in which n is 1 to 5, in particular 1 to 3 and m is 4 to 11, especially 5 to 9.

Interesting groups A are those selected from one of the following groups:

A particularly preferred compound is N- (3,4-dihydroxyphenethyl) -4,4,5,6,6,7,7,8,8,9,9,10,10,11,11,11,11. heptadécafluoroundécanamide

(SuSoS2).

The compounds of formulas AB can be obtained from known compounds using techniques and reactions well known to the organic chemist. For example, N- (3,4-dihydroxyphenethyl) -4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoroundecanamide may be obtained by reacting 2H, 2H, 3H, 3H-perfluoro-undecanoic acid-N-succinimidyl ester and 3-hydroxy-tyrosine acid hydrochloric acid solution in DMF in the presence of N-methylmorpholine.

3- (4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10, 10, 11, 11, 11-heptadecafluoroundecanamido) -6,7-dihydroxy-1,1 dimethyl-1,2,3,4-tetrahydroquinolinium

(SuSoS 3) can be prepared from ANACAT and 2H, 2H, 3H, 3H-

perfluoro-undecanoic acid-N-succinimidyl according to methods analogous to those described by Y. Bethuel. K.

Gademann, J. Org. Chem 2005, 70, 6258; Zrcher, S .;

Wackerlin, D .; Bethuel, Y .; Malisova, B .; Textor, M.;

Tosatti, S .; Gademann, K. Journal of the American Chemical

Society 2006, 128, 1064-1065. 1- (2- (4,4,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoroundecanamido) ethyl) -3,4 dihydroxypyridinium

(SuSoS4) can also be prepared by methods analogous to those mentioned above, starting with 1- (2-aminoethyl) -3,4-dihydroxypyridinium and 2H, 2H, 3H, 3H-perfluoro-undecanoic acid. N-succinimidyl.

N- (3,4-dihydroxyphenethyl) -

3, 3, 4,4,5,5, 6, 6, 7, 7, 8, 8, 9, 9, 10, 10, 10-heptadecafluorodecan-1

(SuSoS5) can also be prepared by methods analogous to those mentioned above, from 3-hydroxy-tyrosine hydrochloric acid and 1,1,1,2,2,3,3,4,4,5,5,6,6,7,8,8,8-heptadecafluoro-10-iododecane.

N- (4,5-dihydroxy-2-nitrophenethyl) -

4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoroundecanamide

(SuSoSβ) can also be prepared by methods analogous to those mentioned above, from 4- (2-aminoethyl) -5-nitrobenzene-1,2-diol and 2H, 2H, 3H, 3H-perfluoro-undecanoic -N-succinimidyl acid.

The solid substrate on the surface of which the self-assembly is made may be any solid substrate involved in the operation of a mechanical movement, in particular consisting of a material selected from among gold, silver, silver steel, including 20AP steel, aluminum, brass, bronze, cuproberyllium, titanium dioxide, ruby, sapphire, silicon, nickel and nickel-phosphorus, as well as other surfaces metal, such as iron, chromium, tantalum, yttrium, silicon, germanium, copper, platinum, and metal or ceramic oxides, such as zirconia and niobium (niobium oxide), list not being limiting. As a substrate, it is also possible to use polymers such as polyethylenes, polystyrols, polyamides, polydimethylsiloxanes, polyvinyl chlorides and epoxy resins, this list not being so limiting. The substrate may also be a substrate in one of these materials or another whose surface has been coated or coated, for example by a galvanic deposition of gold, gold-copper-cadmium and gold, nickel, rhodium, tin-nickel, or anodized, as in the case of aluminum alloy or titanium parts, or modified by a surface treatment such as oxidation, carburization or nitriding.

The thickness of the ultra-thin layer measured in ellipsometry is generally 0.5 to 10 nm, a higher value which will be retained for the definition of ultrathin, preferably 1 to 4 nm.

To be effective as an epilame, that is to say to prevent satisfactory oil spreading, the contact angle in advance with the water must generally be at least 100 °.

Preferably the ultra-thin layer of formula A-B remains functional as epilame after two watch washes.

The invention also relates to a timepiece characterized in that it comprises an ultra-thin layer as defined above.

The invention also relates to a process for preparing the ultra-thin layer defined above, characterized in that it comprises immersing the substrate in a solution of the compound of formula AB, for example in water, or a mixture of water and protic solvent such as, for example, 2-propanol. This process does not use a fluorinated solvent and is therefore respectful of the environment.

The invention will be better understood with the aid of the following examples which have an illustrative and nonlimiting character.

Example 1 Synthesis of N- (3,4-dihydroxyphenethyl) -4,4,5,5,6,6,7,7,8,8,9,9,9,10,10,11,11,11-heptadecafluoroundecanamide ( SuSoS2)

Synthesis of 2H, 2H, 3H, 3H-perfluoro-undecanol-acid-N-succinimidyl ester 2H, 2H, 3H, 3H-perfluoro-undecanoic acid (1.354 g, 2.75 mmol), N-hydroxysuccimide (348 mg, 3.02 mmol), dicyclohexylcarbodiimide (622 mg, 3.02 ramol) were dissolved in ethyl acetate (120 ml) and mixed for 18 hours at room temperature. The white precipitate formed (dicyclohexylurea DCU) was filtered and the remaining solution evaporated to dryness. The residue was recrystallized twice from ethyl acetate. Yield 1.00 g (62%) containing traces of DCU.

¹ H NMR (CDCl ₃ , 300 MHz, ppm): 3.0 (m, 2H CH ₂ ), 2.88 (s, 4H CH ₂ NHS), 2.6 (m, 2H CH ₂ ).

Synthesis of N- (3,4-dihydroxyphenethyl) -4,4,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoroundecanamide

Hydrochloric acid 3-hydroxy-tyrosine (257.5 mg, 1.35 mmol) and N-methylmorpholine (241 μl) were dissolved in DMF (8 ml). Perfluoro-NHS-ester (800 mg) was added and the mixture was stirred under a nitrogen atmosphere overnight. Water (40 ml) was added, the precipitate formed filtered off and washed with water. The solid was dissolved in ethyl acetate and the organic phase was dried with magnesium sulfate. The solvent was evaporated and the residue was recrystallized from chloroform (30 ml,

4 ° C). Yield 752 mg (88%).

Molecular weight: 627.29

% by weight: C 36.38; H, 2.25; F 51.49; N, 2.23; O 7.65 without H: C 47.5; F 42.5; N 2.5; O 7.5 ¹ H NMR (CDCl ₃ , 300 MHz, ppm): 8.7 (bs, 2H OH), 8.08 (t, 1H NH), 6.7-6.4 (m, 3H dopamine), 3.2 (q, 2H CH ₂ ), 2.7-2.3 (m, 6H CH ₂ ).

corresponding to N- (3,4-dihydroxyphenethyl) -4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoroundecanamide

Example 2 Preparation of dipping solutions and immersion of different substrates therein

Preparation of SuSoS2 soaking solution

SuSoS2 (0.052 mmol) 33 mg was dissolved in 35 ml of 2-propanol in a graduated 100 ml flask and shaken until completely dissolved. Ultrapure water was added to the mark and shaken vigorously, which increased the temperature of the solution. After returning the solution to room temperature, a few drops of water were added to adjust the volume to 100 ml. The solution was sonicated for 10 seconds to degas it and allow complete mixing of water and 2-propanol.

Immersion of gold, polished steel, titanium oxide and ruby substrates in soaking solutions

Samples of gold, polished steel, aluminum, titanium oxide and rubies were cleaned in a UV / ozone chamber for 30 minutes and immersed overnight in the SuSoS2 solution. The samples were then immersed in 2-propanol for 10 seconds, rinsed with 2-propanol and dried with a stream of nitrogen. In the case of steel, the surfaces were lightly polished with a wipe soaked in 2-propanol, rinsed with additional 2-propanol and dried with nitrogen flow.

Example 3 Analysis of ultra-thin layers formed by self-assembly on different substrates

Monolayers formed by self-assembly on the different substrates were analyzed by variable angle spectroscopic ellipsometry (VASE: Variable Angle

Spectroscopic Ellipsometry; cf. Feller et al. (2005). "Influence of poly (propylene sulfide-block-ethylene glycol) di-and triblock copolymer architecture on the formation of molecular adlayers on their surfaces and their effect on protein resistance: A candidate for surface modification in biosensor research.", Macromolecules 38 (25 ): 10503-10510), dynamic contact angle measurement

(dCA: Dynamic Angle Contact;

Tosatti et al. (2002) "Self-Assembled

Monolayers of Dodecyl and Hydroxy-dodecyl Phosphates on Both Smooth and Rough

Titanium and Titanium Oxide Surfaces ", Langmuir 18 (9): 3537-3548, as follows: Surface wettability was determined by measuring the angles of contact in advance and recoil on a sessile (water) drop (Contact Angle Measuring System, G2 / G40 2.05-D, Kruss GmbH, Hamburg, Germany); the experiment was conducted automatically by increasing and decreasing the size of the drop at a rate of 15 ml per minute; 480 values were measured for the advance contact angle and 240 for the recoil contact angle, at 3 different locations for each sample); the data collected was analyzed by the tangents 2 method (Drop-Shape Analysis program adjustment routine in Version DSA 1.80.0.2 for

The different substrates used are

silicon wafers coated with a thin layer of gold - polished steel disks polished ruby disks aluminum plates silicon wafers coated with a thin layer of titanium dioxide The main parameters measured by VASE and CA are assembled in Table 1 below.

Table 1: Thickness measured by ellipsometry and advance contact angles with water

The X-ray photoelectron spectroscopy (XPS) analysis shows that the SuSoS2 molecules are present on all surfaces by the detection of the N and F elements. These results show that an ultra-thin layer is obtained on all the substrates tested. from SuSoS2.

Advantageous contact angle values with water are satisfactory for use as epilam (greater than 100 °).

EXAMPLE 4 Comparison of the ultra-thin layers formed by self-assembly of SuSoS2 and Fixodrop FK-BS on surfaces of gold, polished steel and ruby.

1) Preparation of the ultra-thin layers of SuSoS2 and Fixodrop on the surfaces of the different substrates

An ultra-thin layer of SuSoS2 is coated with substrates of gold, polished steel and ruby as described in Example 2. The surface appearance is excellent and no markings can be distinguished due to the deposit .

An ultra-thin layer of Fixodrop FK-BS is coated with gold, polished steel and ruby substrates as specified by the manufacturer by dipping the substrates in a solution of tetradecafluorohexane.

The thickness of this layer measured by ellipsometry on gold is 0.7 nm for SuSoS2 and 1.7 nm for Fixodrop.

2) Measurement of contact angles with different solvents and determination of surface energies

Advance contact angles with water, hexadecane, diodomethane and ethylene glycol were measured by dynamic contact angle goniometric technique similar to that used in Example 3.

The dispersive and polar components of surface energy were deduced from these measurements with the Owens-Wendt model (Owens DK and Wendt R. C, 1969, Journal of Applied Polymer Science, 13, 8, 1741). ).

The main results obtained are summarized in Table 2 below.

Table 2; Contact angles and surface energies with different solvents

For gold, steel and ruby, the contact angles with water, hexadecane, diodomethane and ethylene glycol are acceptable for use as epilam, and comparable with those measured for Fixodrop.

For gold, steel and ruby, the layer formed with SuSoS2 shows a dispersive character only, as expected for a molecule of this type. The surface energy seems to vary with the material, but is in any case below 20 mJ / m ² . The weakest energy (and therefore a priori the best holding) is obtained for steel, followed by ruby and gold. 3) Measurement of spreading lubricants

The spreading of the lubricants on a surface is characterized by measuring the average diameter of a drop of typically 0.5 mm in diameter immediately after the drop has been deposited and after 20 minutes. The spread corresponds to the relative variation of the average diameter after 20 minutes. A good performance of a lubricant corresponds to a spread of 2% or less. Spreading greater than 10% is noticeable in the eye and is not acceptable. The oils used for the tests are a watch oil "941" (house Moebius and Fils, mixture of alkyl-aryl-monooleate and two C _3.0 -C ₁₃ di-esters, viscosity of 110 cSt at 20 ⁰ C, surface tension of 32.8 mN / m) and a test oil CESNIII (Swiss Laboratory for Watchmaking Research, silicone oil, surface tension of 23.1 mN / m, "Watchmaking Switzerland" No 43, 7.11.1974).

The spread obtained on steel, ruby and gold surfaces coated with the SuSoS2 molecule, as well as a gold surface coated with the commercial product Fixodrop FK-BS of the Moebius et Fils house, is compared according to the manufacturer's instructions. For the SuSoS2 molecule, the spread is in all cases less than 1%, and is comparable to that measured for the Fixodrop, as shown by the table below.

Table 3: Spreading lubricants

4) Conclusion

For all the surfaces studied, the contact angle obtained on the ultra-thin layers made with the SuSoS2 molecule is greater than 100 °, the surface energy is less than 20 mJ m ^-2 , and the spread is less than

1%.

The properties of the SuSoS2 ultra-thin layer are at least as good as those obtained with the commercial product Fixodrop, and the solvent used for the dipping is environmentally friendly.

Claims

1. Hydrophobic and oleophobic ultra-thin layer formed by self-assembly on a solid substrate surface of compounds of the general formula

A-B wherein A represents a group of formula

in which

Z represents C or N ⁺ ,

X represents CH or CL, L being an electron-withdrawing group chosen from F, Cl, Br, I, CF ₃ , NO ₂ and

N (CH ₃ ) ₃ % Y represents H or CH ₃ , or Y forms with X a heterocycle of 5 or 6 atoms,

T represents NH, CO, CONH or NH ₂ ⁺ U ^" , U ^" being a soluble anion such as for example F ^" , Cl ^" , Br ^" , I, OH ^" ,

NO ₃ ^" , HSO ₄ ^" , SO ₄ ^{2 "} , CO ₃ ^2" , HCO ₃ ^" or SCN ^" , and B represents a linear aliphatic Cα-C20 alkyl group partially or completely substituted with F.

2. ultra-thin layer according to claim 1, characterized in that B is a linear aliphatic group perfluorinated in its terminal part of formula (CH ₂ ) _n - (CF ₂ ) _m CF ₃ in which n is 1 to 5 , and m is 4 to 11.

Ultra-thin layer according to claim 2, characterized in that n is 1 to 3 and m is 5 to 9.

4. Ultrathin layer according to one of the preceding claims, characterized in that A is chosen from one of the following groups:

5. Ultrathin layer according to one of the preceding claims characterized in that it is obtained from N- (3,4-dihydroxyphenethyl) - 4,4,5,5,6,6,7,7, 8,8,9,9,10,10,11,11,11- heptadecafluoroundecanamide.

6. ultra-thin layer according to one of the preceding claims, characterized in that the solid substrate is made of a material selected from gold, silver, steel, aluminum, brass, bronze , cuproberyllium, titanium dioxide, ruby, sapphire, silicon, nickel and nickel-phosphorus, as well as other metallic surfaces, such as iron, chromium, tantalum, yttrium, germanium, copper, platinum, and metal or ceramic oxides, such as zirconia or niobia (niobium oxide), or polymers such as polyethylenes, polystyrols, polyamides, polydimethylsiloxanes, polyvinyl chlorides, epoxy resins, or a substrate of one of these materials or another whose surface has been coated or coated, for example by a galvanic deposition of gold, gold-copper-cadmium and gold, nickel, rhodium, ^one of tin-nickel, or treated by anodization, as in the case of parts made of aluminum alloy or titanium, or modified ^'by a surface treatment such as oxidation, carburization or nitriding.

7. Ultrathin layer according to one of the preceding claims, characterized in that its contact angle in advance with water is at least 100 °.

8. Ultrathin layer according to one of the preceding claims, characterized in that its thickness measured in ellipsometry is 0.5 to 10 nm.

9. Timepiece, characterized in that it comprises an ultra-thin layer according to one of the preceding claims.

10. A process for preparing an ultra-thin layer according to one of claims 1 to 9, characterized in that it comprises immersing the substrate in a solution of the compound of formula AB in water or a mixture of water and protic solvent.

11. The method of claim 10, characterized in that the protic solvent is 2-propanol.

12. Use of an ultra-thin layer according to one of claims 1 to 9 as an epilame.