Composite particles, coatings and coated articles

Abstract

The invention relates to composite particles, coatings, and coated articles. An article is provided at least partially covered with a coating defining a slippery surface. The coating comprises a layer of particulate material bound to the article and a substantially immobilised lubricant at least partially covering and penetrating into the layer of composite particulate material. The composite particulate material comprises a carrier particle at least partially coated with a hydrophobic material. A further article is provided at least partially covered with a coating comprising a layer of the composite particulate material bound to said article. This is useful in preparation of the article having a coating defining a slippery surface. Methods of preparing the coating and the articles are also provided.

Claims

1. An article at least partially covered with a coating defining a slippery surface, the coating comprising a layer of a composite particulate material bound to said article and a substantially immobilized lubricant at least partially covering and penetrating into said layer of composite particulate material, wherein the composite particulate material comprises carrier particles at least partially coated with a hydrophobic material.

2. An article according to claim 1, wherein the coating further comprises a binder and wherein the composite particulate material is bound to the article by said binder.

3. An article according to claim 2, wherein the binder is an adhesive.

4. An article according to claim 2, wherein the binder is a polymer.

5. An article according to claim 1, wherein the composite particulate material is a powder or a granular material.

6. An article according to claim 1, wherein the carrier particles have recess defining surface irregularities and the hydrophobic material is located at least partially within some or all of the recesses defined by said surface irregularities.

7. An article according to claim 1, wherein the carrier particles comprise or consist of a natural or synthetic mineral, a metal, metal alloy, metal oxide, or metal salt, or a mixture or composite of any of these.

8. An article according to claim 1, wherein the carrier particles comprise aluminium, chromium, cobalt, copper, iron, manganese, silver, tin, niobium, titanium, lead, nickel, zinc, molybdenum, beryllium, boron, phosphorus, arsenic or silicon, preferably in the form of or within an oxide, mixture, alloy, natural or synthetic mineral or composite.

9. An article according to claim 1, wherein the hydrophobic material comprises a silane, fluorosilane, perfluorosilane, organosilicon compound (including silicones and polymerised siloxanes), fluorocarbon, perfluorocarbon, polymer comprising carbon, silicon and fluorine atoms, fluorinated carboxylic acid or ester, perfluorinated carboxylic acid or ester, fatty acid, or fatty ester (including mono-, di and triglycerides), a derivative or salt thereof, or a mixture of any of these.

10. An article according to claim 1, wherein the hydrophobic material comprises perfluorooctyltriethoxysilane, lauric acid, myristic acid, palmitic acid, stearic acid, perfluorooctanoic acid, a derivative or salt thereof, or a mixture of any of these.

11. An article according to claim 1, wherein the lubricant has a viscosity of between about 0.5 cSt to about 110000 cSt at 20 C.

12. An article according to claim 1, wherein the lubricant is an at least partially fluorinated hydrocarbon, a fluorosilane, perfluorosilane, perfluoroalkylether, silicone oil, or a mixture of any of these.

13. An article according to claim 1, wherein the composite particulate material comprises three populations of carrier particles each having different average particle sizes, at least one population of the carrier particles being at least partially coated with a hydrophobic material.

14. An article according to claim 13, wherein the three populations of carrier particles have respective particle sizes in the three size ranges: between about 100 nm and about 2000 m; between about 50 nm and about 100 m; and between about 10 nm and about 50 m.

15. An article according to claim 14, wherein the three populations of carrier particles comprise: MnO particles having an average particle size in the range about 100 m to about 1000 m; Fe particles having an average particle size in the range about 10 m up to about 100 m; Nb.sub.2O.sub.5 or Ta.sub.2O.sub.5 particles having an average particle size in the range about 10 nm to about 50 m.

16. An article at least partially covered with a coating comprising a layer of composite particulate material bound to said article, wherein the composite particulate material comprises three populations of carrier particles each having different average particle sizes, at least one population of the carrier particles being at least partially coated with a hydrophobic material; said article being suitable for use in preparation of an article according to any one of the preceding claims.

17. An article according to claim 16, wherein the three populations of carrier particles have respective particle sizes in the three size ranges: between about 100 nm and about 2000 m; between about 50 nm and about 100 m; and between about 10 nm and about 50 m.

18. An article according to claim 17, wherein the three populations of carrier particles comprise: MnO particles having an average particle size in the range about 100 m to about 1000 m; Fe particles having an average particle size in the range about 10 m up to about 100 m; Nb.sub.2O.sub.5 or Ta.sub.2O.sub.5 particles having an average particle size in the range about 10 nm to about 50 m.

19. A method of preparing a coating defining a slippery surface on an article comprising, binding a composite particulate material to the article to form a superhydrophobic layer on the article, and applying a lubricant to said layer such that the lubricant at least partially covers said particulate material and penetrates at least partially into said layer.

20. A method according to claim 19, wherein the composite particulate material comprises carrier particles at least partially coated with a hydrophobic material.

21. A method according to claim 19, wherein the method further comprises applying a binder to the article.

22. A method according to claim 21, wherein the binder is an adhesive.

23. A method according to claim 21, wherein the binder is a polymer.

24. A method according to claim 21 comprising: applying a binder to the article; applying the composite particulate material to the binder to form a superhydrophobic layer bound to the article; and applying a lubricant to said layer.

25. A method according to claim 21 comprising: combining the composite particulate material with the binder to form a mixture; applying said mixture to the article to form a superhydrophobic layer bound to the article; and applying a lubricant to said layer.

26. A method of preparing a coating defining a slippery surface on an article, the method comprising combining a lubricant with a composite particulate material, and applying a layer of the combined lubricant and composite particulate material to a surface of the article to form a slippery surface wherein the lubricant is substantially immobilized and at least partially covering and penetrating into said layer of composite particulate material.

27. A method according to claim 26, wherein the composite particulate material comprises carrier particles at least partially coated with a hydrophobic material.

28. A method according to claim 26, wherein the composite particulate material is a powder or a granular material.

29. A method according to claim 27, wherein the carrier particles have recess defining surface irregularities and the hydrophobic material is located at least partially within some or all of the recesses defined by said surface irregularities.

30. A method according to claim 27, wherein the carrier particles comprise or consist of a natural or synthetic mineral, a metal, metal alloy, metal oxide, or metal salt, or a mixture or composite of any of these.

31. A method according to claim 27, wherein the carrier particles comprise aluminium, chromium, cobalt, copper, iron, manganese, silver, tin, niobium, titanium, lead, nickel, zinc, molybdenum, beryllium, boron, phosphorus, arsenic or silicon, preferably in the form of or within an oxide, mixture, alloy, natural or synthetic mineral or composite.

32. A method according to claim 27, wherein the hydrophobic material comprises a silane, fluorosilane, perfluorosilane, organosilicon compound (including silicones and polymerised siloxanes), fluorocarbon, perfluorocarbon, polymer comprising carbon, silicon and fluorine atoms, fluorinated carboxylic acid or ester, perfluorinated carboxylic acid or ester, fatty acid, or fatty ester (including mono-, di and triglycerides), a derivative or salt thereof, or a mixture of any of these.

33. A method according to claim 27, wherein the hydrophobic material comprises perfluorooctyltriethoxysilane, lauric acid, myristic acid, palmitic acid, stearic acid, perfluorooctanoic acid, a derivative or salt thereof, or a mixture of any of these.

34. A method according to claim 26, wherein the lubricant has a viscosity of between about 0.5 cSt to about 110000 cSt at 20 C.

35. A method according to claim 26, wherein the lubricant is an at least partially fluorinated hydrocarbon, a fluorosilane, perfluorosilane, perfluoroalkylether, silicone oil, or a mixture of any of these.

36. A method according to claim 26, wherein the composite particulate material comprises three populations of carrier particles each having different average particle sizes, at least one population of the carrier particles being at least partially coated with a hydrophobic material.

37. A method according to claim 36, wherein the three populations of carrier particles have respective particle sizes in the three size ranges: between about 100 nm and about 2000 m; between about 50 nm and about 100 m; and between about 10 nm and about 50 m.

38. A method according to claim 37, wherein the three populations of carrier particles comprise: MnO particles having an average particle size in the range about 100 m to about 1000 m; Fe particles having an average particle size in the range about 10 m up to about 100 m; Nb.sub.2O.sub.5 or Ta.sub.2O.sub.5 particles having an average particle size in the range about 10 nm to about 50 m.

39-42. (canceled)

Description

BRIEF DESCRIPTION OF FIGURES

[0090] For the purposes of example only, embodiments of the invention are described below with reference to the accompanying drawings, in which:

[0091] FIGS. 1 and 2 are graphs which are referred to in the Examples.

[0092] FIG. 3 is a table which includes the data used for the graphs of FIGS. 1 and 2

[0093] FIG. 4 is a selection of scanning electron micrographs of some of the carrier particles referred to herein.

EXAMPLES

Example 1

[0094] Fabrication of Composite Particulate Material

[0095] According to a general method, the hydrophobic material was combined with the carrier liquid and the resultant mixture was stirred until a solution was formed. Carrier particles were then added to the solution and the resultant mixture was stirred until substantially all of the carrier particles were coated with the solution. The mixture was filtered and the carrier liquid was removed via evaporation to provide the composite particulate material.

[0096] Composite particulate material A: 1 wt. % perfluorooctyltriethoxysilane in ethanol base (FAS) was stirred for 2 hours. Particles of MnO (60 mesh) were then added to the mixture. The carrier liquid was allowed to evaporate overnight.

[0097] Composite particulate material B: 1 wt. % perfluorooctyltriethoxysilane in ethanol base (FAS) was stirred for 2 hours, and then particles of Nb.sub.2O.sub.5 (325 mesh) were treated with FAS. The carrier liquid was allowed to evaporate overnight.

[0098] Composite particulate material C: 1 wt. % perfluorooctyltriethoxysilane in ethanol base (FAS) was stirred for 2 hours, and then particles of TiO.sub.2 nanoparticles (sizes range from about 20 to about 300 nm, as determined by SEM) were treated with FAS. The carrier liquid was allowed to evaporate overnight.

[0099] Composite particulate material D: 1 wt. % perfluorooctyltriethoxysilane in ethanol base (FAS) was stirred for 2 hours, and then particles of TiO.sub.2 P25 (average primary particle size 21 nm) were treated with FAS. The carrier liquid was allowed to evaporate overnight.

Example 2

[0100] Method of Binding the Layer of Composite Particulate Material to the Article & Durability Tests

[0101] Three coatings were prepared by fixing composite particles of MnO, Nb.sub.2O.sub.5, iron oxide (the carrier particles) and stearic acid (the hydrophobic material), on glass substrates using double-sided tape.

[0102] Measurement of Contact Angles of the Superhydrophobic Layer

[0103] The contact angles were measured at ambient temperature using the sessile-drop method using an optical contact angle meter (FTA 1000, Surftens 4.5, water droplet is 5 L).

[0104] Measurement of the Durability of the Composite Particulate Layer

[0105] The coatings were then exposed to ultraviolet radiation having a wavelength of 365 nm and 254 nm. The UV light was fully covered and positioned nearly in contact with the samples for a period of 24 hours and then water contact angle (CA) was measured. The results are shown in table 1.

TABLE-US-00001 TABLE 1 MnO + Nb.sub.2O.sub.5 + Iron oxide + Composite Material stearic acid stearic acid stearic acid CA Before UV tests 151.1 154.8 153.3 CA after 365 nm UV 150.1 152.3 150.3 tests CA after 254 nm UV 150.7 150.0 150.3 tests

[0106] As can be seen from Table 1, all of the layers were superhydrophobic before the UV tests, having contact angles of >150 degrees. After exposure to ultraviolet radiation at two different wavelengths the layers remained superhydrophobic. This demonstrates that the superhydrophobic layer is robust enough to withstand high-energy UV radiation.

Example 3

[0107] Fabrication of Coated Articles

[0108] Double-sided adhesive tape was applied to a glass side and then the composite particulate material was applied to the surface of the adhesive tape. The lubricant was then dropped onto the layer of the composite particulate material until the lubricant fully covered and penetrated into the layer of composite particulate material.

[0109] Durability Tests of Coated Article

[0110] Substrate area: 25 mm25 mm SLIPS comprising composite particulate material (carrier particles of TiO.sub.2 having a primary size of approximately 21 nm mixed with TiO.sub.2 having a size range of between about 20 nm and 300 nm coated with perfluorooctyltriethoxysilane) and the lubricant Krytox 104A.

[0111] The mass (g) of the substrate was measured before and after the addition of the lubricant. The substrate was heated to 98 C. (2 C.) and the mass (g) of the substrate was measured every 5 min. The results are shown in table 2.

TABLE-US-00002 TABLE 2 Lubricant Krytox 104A Mass before addition of 4.5239 lubricant Mass after addition of 4.7543 lubricant Mass after 5 min 4.6659 Mass After 10 min 4.6314 Mass After 15 min 4.5908 Mass After 20 min 4.5862 Mass After 25 min 4.5659 Mass After 30 min 4.5590 Mass After 35 min 4.5532

[0112] The results in Table 2 show that the coated article continued to maintain an amount of the lubricant even after 35 minutes of heating.

[0113] The average thickness (m) of the lubricant layer on the surface was calculated from the mass data in Table 2 and knowledge of the density of the lubricant and the area of deposition. The average thickness of the lubricant layer is shown in Table 3.

TABLE-US-00003 Lubricant Krytox 104A Thickness after addition of 199.0 lubricant (m) Thickness (m) after 5 min 122.6 Thickness (m) After 10 min 92.8 Thickness (m) After 15 min 57.8 Thickness (m) After 20 min 53.8 Thickness (m) After 25 min 36.3 Thickness (m) After 30 min 30.3 Thickness (m) After 35 min 25.3

[0114] In order to further demonstrate the durability of the coated article, the liquid contact angle (CA) and contact angle hysteresis (CAH) of the sample was measured at intervals during the heating process. Tilting grade goniometry (TPG) was used to measure the CAH. The results are presented in FIGS. 1 to 3.

[0115] The sample was positioned on a hot plate (set to about 100 C.). Every 5 minutes, the sample was removed from the hot plate, allowed to cool to ambient temperature, and the CA and CAH of water, coffee, red wine and corn oil droplets were measured.

[0116] As seen in FIG. 1, from 0 to 10 min heating, the CA gradually increased, and then jumped to a high level between 10 and 15 min, before stabilising between 15 and 30 min. After heating for 35 min the lubricant no longer evenly covered the substrate; there appeared to be wet regions (regions that appeared to still be coated in the lubricant) and dry regions (regions where the lubricant appeared to have evaporated from). Thus, at 35 min the contact angle measurements were taken from both the wet and dry regions and the results compared. As can be seen, the CA did not change much between dry and wet regions, which shows that even regions that appeared dry still comprised a thin layer of the lubricant, thus maintaining the slippery property.

[0117] FIG. 2 shows that even areas that appeared to be dry after 35 min heating still exhibited a CAH of below 10 degrees. However, it was observed that the sliding motions of liquids were getting slower as the heating time increased. These results demonstrate the durability of the coating and that it maintains its slippery properties, even when the lubricant has been substantially evaporated.

[0118] From the heating tests, it can be concluded that the coating retains its slippery properties (as shown by the CA measurements and the CAH of <15 degrees), even after being heated at 100 C. This demonstrates that coated articles may be fabricated which are durable enough to still function as liquid repellent substrates, even after sustained exposure to high temperatures.

Example 4

[0119] Low-Temperature Test

[0120] An article according to the first aspect of the invention comprising composite particulate material (nanoscale titanium dioxide carrier particles and perfluorooctyltriethoxysilane as the hydrophobic material) and a lubricant (Krytox FC 70) was inserted into liquid nitrogen (about 196 C.) for about 3 s, and then coffee, red wine, corn oil and water were dropped on the surface. Initially, all of the liquids were immobilised on the surface of the article. Then, as the surface returned to room temperature, it reverted back to its slippery form and the liquids were repelled. This demonstrates that the coatings described herein are not damaged when subjected to extremely cold temperatures and, upon returning to ambient temperate, still function as slippery surfaces.

REFERENCES

[0121] 1. Leslie et al., Nat. Biotechnol., 2014, 32, 1134. [0122] 2. Grinthal et al., Chem. Mater., 2014, 26, 698. [0123] 3. Kim et al., Nano Lett., 2013, 13, 1793. [0124] 4. MacCallum et al., ACS Biomater. Sci. Eng., 2015, 1, 43. [0125] 5. Wilson et al., Phys. Chem. Chem. Phys., 2013, 15, 581.