Method for forming oleophobic-hydrophilic coatings including particles and/or nano-particles, a coating formed thereby and an article to which the coating is applied

Abstract

The invention to which this application relates is apparatus and a method for applying coatings to improve the ability to provide Oleophobic and/or Hydrophilic surfaces on an item and the coating includes particles and/or nano particles to enhance the performance characteristics of the coating.

Claims

1. A method for the formation of a coating having oleophobic and hydrophilic properties, said method comprising the steps of: preparing a polymer or mixed polymer solution; preparing a surfactant or mixed surfactant solution; adding the surfactant or mixed surfactant solution to the polymer or mixed polymer solution to form a mixture applying the mixture to a surface to form the said coating thereon and wherein particles and/or nano-particles are dispersed in the polymer or mixed polymer solution prior to combination of the same with the surfactant or mixed surfactant solution.

2. The method according to claim 1 wherein the said mixture is agitated to create a precipitate.

3. The method according to claim 2 wherein the precipitate is a solid precipitate.

4. The method according to claim 3 wherein the precipitate is dissolved in a solvent or solvent mixture to create a complex precipitate in solution or suspension.

5. The method according to claim 4, wherein the said solution or suspension, once applied to a surface, is allowed to form the said coating.

6. The method according to claim 1 wherein an increase in loading of particles or nano-particles is used to change the said mixture from solution to a suspension.

7. The method according to claim 1 wherein the particles and nano-particles are any, or any combination of, silica, titania, zinc oxide, zirconia, indium tin oxide, inorganic materials, polymeric materials, carbon black, nanotubes, quantum dots, diamond, graphene, silesquioxanes, or clays.

8. The method according to claim 1 wherein the dispersal of the particles and nano-particles is performed ultrasonically for 1 hour.

9. The method according to claim 1 wherein the surfactant or mixed surfactant solution is added to the polymer or mixed polymer solution in a dropwise manner.

10. The method according to claim 1 wherein the surfactant or mixed surfactant solution is added to the polymer or mixed polymer solution in a ratio of 1:4.

11. The method according to claim 3 wherein the solid precipitate is heated to drive off water.

12. The method according to claim 11 wherein after heating the solid precipitate is washed with water and then is dried again by heating prior to dissolving the same in a solvent or solvent mixture to form a complex precipitate in solution.

13. The method according to claim 4 wherein a loading of particles or nanoparticles are dispersed in the solution or suspension containing the dissolved complex precipitate.

14. The method according to claim 6 wherein the forming of the coating by the solution or suspension is achieved by any or any combination of application by dipping, solvent casting, spin coating, spraying, nubulisation or atomisation, flow coating, vapour deposition, plasma deposition, UV deposition, e-beam deposition, and/or evaporative deposition.

15. The method according to claim 1 wherein the mixture further includes a mixed solvent.

16. A coating formed from the method according to claim 1.

Description

(1) Specific embodiments of the invention are now described; wherein

(2) FIG. 1 illustrates graphically the switching parameters for several coatings formed in accordance with embodiments of the invention;

(3) FIG. 2 illustrates graphically the Vickers hardness number measured for various forces in relation to a coating formed in accordance with one embodiment of the invention;

(4) FIG. 3 illustrates oil-water separation performance of different mesh formations;

(5) FIG. 4 illustrates the separation of an oil-water mixture using a PDDA-3% SiO2 (7 nm)-anionic fluorosurfactant coated mesh in accordance with the invention.

(6) Oleophobic-hydrophilic switching parameters for various PDDA-particle-anionic fluorosurfactant complex coatings at 3% w/v particle loading in PDDA-particle precursor solution. Switching parameters are calculated from the difference between the hexadecane and water static contact angles (after 10 s).

(7) In accordance with the invention the aim is to provide a coating which includes particles and/or nano-particles therein and which can be formed using a method which is improved in terms of reliability and practical application, thereby allowing the same to be commercially implementable.

(8) In addition to the method used, it is also necessary to select the materials which are used in the method steps. For example, in preferred embodiments, the unfunctionalised or functionalised particles or nanoparticles that are used are silica and/or comprise colloidal metals (such as gold, platinum, palladium, copper, silver, rhodium, rhenium, nickel, and iridium) having surface positive/negative charge, and/or alloys of metals (such as platinum/iridium) having surface positive/negative charge, and/or metal non-oxides (such as titanium nitride, Group II-VI, III-V, and IV quantum dots) having surface positive/negative charge, alkaline earth metal oxides (such as beryllium oxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide) having surface positive/negative charge, transition metal oxides having surface positive/negative charge, transition metals having surface positive/negative charge, lanthanide metal oxides (such as lanthanum oxide, neodymium oxide) having surface positive/negative charge and/or ceramics (such as titanium oxide, zirconium oxide, aluminium oxide, iron oxide, tungsten oxide, cerium oxide, antimony oxide, silicon oxide) having surface positive/negative charge, silsesquioxanes, diamond, titania, zinc oxide, zirconia, indium tin oxide, inorganic materials, silicates, aluminosilicates or polymeric materials. Other variants can include unfunctionalised or functionalised layer materials (such as graphenes, clays, micas, transition-metal dichalcogenides) with surface positive/negative charge.

(9) With regard to the polymer, cationic polymers with the positive charge are selected to be water-soluble and comprise a monomer selected from the group consisting of allylamine, ethyleneimine, quaternary ammonium polymers, polyalkylammonium polymers, polyalkyleneimine based polymers, diallyl dialkyl ammonium salts (e.g. diallyl dimethyl ammonium chloride), dialkylaminoalkyl acrylate (e.g. dimethylaminoethyl acrylate), dialkylaminoalkyl methacrylate (e.g dimethylaminoethyl methacrylate), dialkylaminoalkyl acrylamide (e.g. dimethylaminopropyl acrylamide), dialkylaminoalkyl methacrylamide (e.g. dimethylaminopropyl methacrylamide), dimethylaminoethylaminopropylmethacrylamide methosulfate, methylacrylamide, acrylamidoalkyl trialkylammonium salts (e.g. methacrylamido propyl trimethyl ammonium chloride), N-vinylformamide, N-vinylacetamide, propyleneimine, quaternary ammonium salts of substituted acrylamide, quaternised alkyl amino acrylate esters and amides, acryloyloxyalkyl trialkylammonium salts (e.g. methacryloyloxyethyl trimethylammonium chloride), acrylamidoalkyl trialkylammonium salts (e.g. acrylamidopropyl trimethylammonium chloride), vinylpyridinium salts, quaternised vinylimidazole polymers, 1-vinylimidazolium salts, 2-vinylimidazolium salts, 4-vinylimidazolium salts, 2-vinyl N-alkyl quaternary pyridinium salts, 2-vinyl pyridinium salts, 3-vinyl pyridinium salts, 4-vinyl pyridinium salts, 2-vinyl N-alkyl pyridinium salts, 3-vinyl N-alkyl pyridinium salts, 4-vinyl N-alkyl pyridinium salts, 2-vinylbenzyltrialkylammonium salts, 3-vinylbenzyltrialkylammonium salts, 4-vinylbenzyltrialkylammonium salts, 1-vinyl piperidinium salts, 2-vinyl piperidinium salts, 3-vinyl piperidinium salts, 4-vinyl piperidinium salts, 3-alkyl 1-vinyl imidazolium salts, 2-vinylpyrazine, and copolymers thereof, or is a water-soluble polymer selected from the group consisting of chitosan, chitosan derivatives bearing cationic groups, guar derivatives bearing cationic groups, a polysaccharide bearing cationic groups, and combinations thereof.

(10) Typically the anionic polymer with the negative charge is selected to be water-soluble and comprises a monomer selected from the group consisting of acrylic acid, aspartic acid, allylsulfonic acid, allylphosphonic acid, acrylamidoalkyl alkylphosphonic acid (e.g. acrylamidomethylpropanephosphonic acid), acrylamido alkylsulfonic salts (e.g. 2-acrylamido propane sulfonic salt), citraconic acid, fumaric acid, glutamic acid, itaconic acid, itaconic anhydride, maleic acid, maleic anhydride, methacrylic acid, dime thylacrylic acid, ethylacrylic acid, mesaconic acid, methylenemalonic acid, methallylsulfonic acid, methylmalonic anhydride, styrenesulfonic acid, 3-sulfopropyl acrylate, 3-sulfopropyl methacrylate, vinylacetic acid, vinylsulfonic acid, vinylalcohol, vinyl phosphonic acid, vinyl sulfate, and copolymers thereof.

(11) In addition or alternatively amphoteric polymers which contain positive and negative charges, such as amphoteric polyacrylamide, and acrylic amphoteric polymers (see U.S. Pat. No. 5,011,898) could be used.

(12) With respect to surfactants used, the surfactant can be cationic, anionic, amphoteric, or zwitterionic.

(13) With respect to surfactants used, the tail groups of some or all can be low surface energy including fluoro-substituted and/or branched and/or siloxane.

(14) With respect to surfactants used, the cationic surfactant which is used can be selected from those that comprise ammonium compounds such as those available under the Trade Names Chemguard S-106A, Fluowet 3658, Fluowet NMQ, and the like. Alternatively cationic surfactants based on a cyclic amine or imine, eg. cationic surfactants containing pyridinium groups, imidazolinium groups, piperidinium groups, oxazolinium groups or pyrimidinium groups are also suitable for use. Alternatively, metallosurfactants are also suitable for use.

(15) The Anionic surfactant used preferably includes phosphates such as those sold under the trade name DuPont Capstone FS-63. The anionic surfactant may also comprise carboxylates, such as those sold under the tradename DIC MEGAFACE F-410, and/or may comprise sulfosuccinates such as those sold under the tradename Dow Triton GR-5M and/or may comprise sulfates such as those sold under the trade name Dow Triton W-30 and/or may comprise sulfonates such as those sold under the trade name Chemguard S-103A and/or comprise phosphate esters such as those sold under the trade names Chemguard S-760P, Chemguard S-761P, Chemguard S-764P and/or may comprise carboxylic acids such as perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic acid, perfluoroundecanoic acid, perfluorododecanoic acid, perfluorotridecanoic acid, perfluorotetradecanoic acid, and the like.

(16) Further suitable anionic surfactants include sulfated fatty acid alkanolamines, α-sulfofatty acid esters or fatty acid mono-glycerides. Other suitable anionic surfactants are fatty acid esters or fatty acid sarcosides, fatty acid glycolates, fatty acid lactates, fatty acid taurides or fatty acid isothionates.

(17) The anionic surfactants may also be present in the form of sodium salts, potassium salts or ammonium salts or as soluble salts of organic bases such as mono-, di- or triethanolamine or other substituted amines and/or may include the alkali metal salts of the natural fatty acids.

(18) In one embodiment the amphoteric surfactant used can comprise amine-oxides such as those sold under the trade name DuPont Capstone FS-51, Fluowet OX, Chemguard S-111, and/or comprises betaines such as those sold under the trade name DuPont Capstone FS-50 and/or amphoteric surfactant comprising sulfobetaines such as those sold under the trade name Fluowet SA.

(19) In order to allow a comparison of the invention a method was performed to form a coating without particles/nano-particles being added and a method in accordance with the invention including the addition of particles/nano-particles was performed.

(20) In both the method using the conventional non-particle/nano-particle approach and the method in accordance with the invention, the materials used were a Polymer in the form of poly(diallyldimethylammonium chloride) and a fluorosurfactant in the form of Anionic DuPont Capstone FS-63 (19 mN/m at 0.1% A.I.) or Amphoteric DuPont Capstone FS-50 (15.5 mN/m at 0.1% A.I.).

(21) In the method of the invention the nano particles added were silica nano particles in the form of Degussa Aerosil 300 (particle size=7 nm, negatively charged)

(22) A separate polymer solution was used in the form of a 2% w/v polymer solution in water and a 5% v/v fluorosurfactant solution in water formed the separate fluorosurfactant solution.

(23) In the method without the use of nano-particles the following steps were used:

(24) The fluorosurfactant solution was added dropwise to the polymer solution in a 1:4 ratio, and the mixture was shaken for 1 hour to make a solid precipitate.

(25) 2. The resulting polymer-fluorosurfactant complex precipitate in solution was then placed on a hotplate set at 110° C. to drive off water.

(26) 3. Then the remaining polymer-fluorosurfactant complex precipitate was washed with water before being dried again on a hotplate set at 110° C.

(27) 4. The precipitate was then dissolved in a solvent or solvent mixture (for example ethanol to make a 1% w/v solution).

(28) 5. This solution was then used to form the coating by for example dipping, solvent casting, spin coating, spraying, nebulisation or atomisation.

(29) 6. The coating was allowed to dry through solvent evaporation.

(30) In the method including the use of nano-particles the following method steps were used:

(31) 1. Various loadings of particles or nanoparticles (for example silica nanoparticles, graphene, clays, silsesquioxanes or variants thereof) were ultrasonically dispersed in the polymer solution for 1 hour.

(32) 2. The fluorosurfactant solution was added dropwise to the polymer solution containing particles or nanoparticles in a 1:4 ratio, and the mixture was shaken for 1 hour to make a solid precipitate.

(33) 3. The resulting polymer-particle/nano-particle-fluorosurfactant complex precipitate in solution was then placed on a hotplate set at 110° C. to drive off water.

(34) 4. Then the remaining polymer-fluorosurfactant-particle/nanoparticle complex precipitate was washed with water before being dried again on a hotplate set at 110° C.

(35) 5. The precipitate was then dissolved in a solvent or solvent mixture (for example ethanol to make a 1% w/v solution).

(36) 6. This solution is then used to form the coating by for example dipping, solvent casting, spin coating, nebulisation, spraying, or atomisation.

(37) 7. The coating was allowed to dry through solvent evaporation.

(38) The following tables 1 and 2 set out the results achieved for coatings formed using the two methods and illustrate the clear and significant advantages obtained in terms of the oleophobic and hydrophilic characteristics and improved switching parameter value (the difference in measured static contact angle between oil and water droplets) obtained by using the coating including nano-particles.

(39) TABLE-US-00001 TABLE 1 Water Hexadecane Switching Capstone FS-50 1 μL 1 μL Parameter Amphoteric t = 10 s/° t = 10 s/° t = 10 s/° Poly(diallyldimethylammonium 19 ± 6  86 ± 2 67 chloride) + Capstone FS-50 Poly(diallyldimethylammonium <10 142 ± 3 132 chloride) + Capstone FS-50 + SiO.sub.2 nanoparticles

(40) TABLE-US-00002 TABLE 2 Hexadecane Switching Capstone FS-63 Water 1 μL 1 μL Parameter Anionic t = 10 s/° t = 10 s/° t = 10 s/° Poly(diallyldimethylammonium 20 ± 6  93 ± 3 73 chloride) + Capstone FS-63 Poly(diallyldimethylammonium 10 ± 1 140 ± 7 130 chloride) + Capstone FS-63 + SiO.sub.2 nanoparticles

(41) In one example in accordance with the invention, Poly(diallyldimethylammonium chloride) (PDDR; manufactured by Sigma-Aldrich Ltd.) was used as the polymer and an Anionic fluorosurfactant (Capstone FS-63, DuPont Ltd.) or amphoteric fluorosurfactant (Capstone FS-50, DuPont Ltd.) were used and the results are detailed below in which the particles tested are detailed in Table 3.

(42) TABLE-US-00003 Details of the particles used. Average Particle Surface Particle Supplier Size Charge SiO.sub.2 Degussa Aerosil ® 300 7 nm Negative SiO.sub.2 Crosfield Catalysts 100 μm Negative SiO.sub.2, Degussa Aerosil ® 12 nm Negative methacryloyl R711 (100-200 nm functionalised average aggregate size) SiO.sub.2, Degussa Aerosil ® 12 nm Negative hexadecylsilane R816 functionalised Al.sub.2O.sub.3 Degussa 13 nm Positive Aluminiumoxid C Graphene Strem Chemicals <2 μm Negative ZnO Sigma Aldrich Ltd. <100 nm Positive

(43) In order to test the switching parameter which was obtained the following results were achieved as indicated below in tables 4.1-4.4

(44) TABLE-US-00004 TABLE 4.1 Water and hexadecane static contact angles for glass slide substrates spray coated with PDDA-FS-63/SiO2. Water Switching SiO.sub.2 content/ 1 μL Hexadecane parameter w/v (t = 10 s)/° 1 μL/° (t = 10 s)/° .sup. 0% 22 ± 2  90 ± 2 68 3.0% <10 138 ± 5 128 4.0% <10 135 ± 3 125

(45) TABLE-US-00005 TABLE 4.2 Water and hexadecane static contact angles for glass slide substrates coated by solvent casting with PDDA-FS-63/SiO2. Water Switching SiO.sub.2 content/ 1 μL Hexadecane parameter w/v (t = 10 s)/° 1 μL/° (t = 10 s)/° .sup. 0% 20 ± 6  93 ± 3 73 2.0% 16 ± 3 142 ± 4 126

(46) TABLE-US-00006 TABLE 4.3 Water and hexadecane static contact angles for glass slide substrates spray coated with PDDA-FS-50/SiO2. Water Switching SiO.sub.2 content/ 1 μL Hexadecane parameter w/v (t = 10 s)/° 1 μL/° (t = 10 s)/° .sup. 0% 14 ± 1  82 ± 1 68 1.5% 12 ± 2 131 ± 5 119

(47) TABLE-US-00007 TABLE 4.4 Water and hexadecane static contact angles for glass slide substrates coated by solvent casting with PDDA-FS-50/SiO2. Water Switching SiO.sub.2 content/ 1 μL Hexadecane parameter w/v (t = 10 s)/° 1 μL/° (t = 10 s)/° .sup. 0% 19 ± 10  80 ± 1 61 1.5% <10 142 ± 3 132

(48) With regard to the accompanying Figures, FIG. 1 illustrates Oleophobic-hydrophilic switching parameters for various PDDA-particle-anionic fluorosurfactant complex coatings at 3% w/v particle loading in PDDA-particle precursor solution. Switching parameters are calculated from the difference between the hexadecane and water static contact angles (after 10 s). It will be seen that the switching parameter value/° is significantly increased when the particles/nanoparticles are present in comparison to the value when no particles are present, as indicated by the column with the heading None.

(49) FIG. 2 illustrates graphically the Vickers hardness numbers which are measured for various forces as a function of a 7 nm SiO.sub.2 particle loading concentration for a PDDA-SiO.sub.2-anionic fluorosurfactant which has been applied by spray coating onto silicon wafer substrates. Micro-indentation measurements show that, for a given indentation force, the hardness of the coating increases with the increased loading of silica nanoparticles in the coating which has been applied.

(50) FIG. 3 illustrates in the respective photographs which shows apparatus in accordance with one embodiment of the invention and in a schematic test format for ease of illustration. As shown in FIGS. 3a-c there are provided three articles 2, 4, 6 in the form of a mesh filter. In photograph a. the mesh 2 is an uncoated metal mesh, in photograph b there is provided the same metal mesh 4 but this time at least the upper surface is coated with PDDA-anionic fluorosurfactant complex coating and in Figure c. there is provided the same metal mesh structure 6 and, in accordance with the invention, the mesh is coated with PDDA-3% SiO2 (7 nm)-anionic fluorosurfactant complex coating (coating includes particles). In all cases the same oil-water mixture was poured into the top surface 16 of the mesh and in photograph a. it is seen how the mixture passes through the mesh so that both oil 8 and water 10 are collected in the collecting jar 12. However with both the PDDA-anionic fluorosurfactant complex coating of Photograph b. and the PDDA-3% SiO2-anionic fluorosurfactant coating of photograph c. there is caused separation of the oil 8 and water 10 by the coated mesh 4,6 respectively, with the oil 8 being retained on the top surface of the mesh and only the water 10 collecting in the jar 12. Thus, relatively high-purity water 10 passes through the coated meshes of photographs b and c, whilst oil (hexadecane) 8 is retained on the surface of the mesh 4,6 on which the mixture contacts so providing proof that mesh coated with a coating in accordance with the invention can be used to separate oil 8 from water 10.

(51) Thus, by inclining the coated mesh 6 of photograph c of FIG. 3 above two collecting jars 12, 14 as shown in FIGS. 4a-c, an oil-water mixture can be separated with oil 8 passing into one collecting jar 14 from the top surface 16 of the mesh 6 in accordance with the invention and water 10 passing into the other collecting jar 12 by passing though the mesh as shown progressively in the photographs a-c of FIG. 4 in which the separation of the oil-water mixture using the mesh with the PDDA-3% SiO2 (7 nm)-anionic fluorosurfactant coating is shown being performed.