Liquid-repellent coatings
The invention relates generally to liquid-repellent coatings, and in particular, to porous liquid-repellent coatings, a method of preparing the porous liquid-repellent coatings, and a method of characterizing a porous surface for the liquid-repellent coatings. The invention further relates to a porous liquid-repellent coating comprising a porous layer of a transition metal oxide and/or hydroxide and a layer of a liquid-repellent compound deposited onto the porous layer of the transition metal oxide and/or hydroxide, wherein the porous layer of the transition metal oxide and/or hydroxide is comprised of a plurality of surface pores of varying angles with an average angle that is re-entrant.
1. A porous liquid repellent coating comprising:
a porous layer of a transition metal oxide and/or hydroxide; and
a layer of a liquid-repellent compound deposited onto the porous layer of the transition metal oxide and/or hydroxide,
wherein the porous layer of the transition metal oxide and/or hydroxide comprises a plurality of surface pores of varying angles with an average angle that is reentrant,
wherein at least one of the plurality of surface pores has a reentrant angle of less than 90°, wherein at least one of the plurality of surface pores has an angle of more than 90°, and wherein the porous liquid repellent coating provides a water contact angle of more than 150°.
2. The coating of claim 1 , wherein based on a Gaussian distribution model for the angles of the plurality of surface pores, the standard deviation σ 0 of the angles with respect to the average reentrant angle Ψ 0 is between 0 and 60°.
3. The coating of claim 2 , wherein the standard deviation σ 0 is between 0 and 40°.
4. The coating of claim 1 , wherein the transition metal oxide and/or hydroxide of the porous layer is selected from the group consisting of zinc oxide/hydroxide, nickel (II) oxide/hydroxide, nickel (III) oxide/hydroxide, manganese (II) oxide/hydroxide, manganese (III) oxide/hydroxide, manganese (IV) oxide/hydroxide, manganese (VI) oxide/hydroxide, manganese (VII) oxide/hydroxide, copper (I) oxide/hydroxide, copper (II) oxide/hydroxide, cobalt (II) oxide/hydroxide, cobalt (III) oxide/hydroxide, iron (II) oxide/hydroxide, iron (III) oxide/hydroxide, and a mixture thereof.
5. The coating of claim 4 , wherein the transition metal oxide/hydroxide of the porous layer is zinc oxide/hydroxide or manganese (IV) oxide/hydroxide.
6. The coating of claim 1 , wherein the liquid-repellent compound is a fluorocarbon polymer or compound.
7. The coating of claim 1 , wherein the liquid-repellent compound is a fluoroalkylsilane (FAS) or alkylsilane.
8. The coating of claim 7 , wherein the liquid-repellent compound is 1H,1H,2H,2H-perfluorododecyltrichlorosilane, 1H, 1H,2H,2H-perfluorooctyltrichlorosilane (PFOS), 1H, 1H,2H,2H-perfluorodecyltrimethoxysilane, 1H, 1H,2H,2H-perfluorodecyltrichlorosilane, or octadecyltrichlorosilane.
9. The coating of claim 6 , wherein the liquid-repellent compound is polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or perfluorooctyl polyhedral oligomeric silsesquioxane (PFO-POSS).
10. The coating of claim 1 , wherein the liquid-repellent compound is an aminosilane polymer or compound.
11. A method of preparing the porous liquid-repellent coating of claim 1 on a substrate, the method comprising: immersing a substrate in a solution of a transition metal nitrate salt and a weak base at a temperature range of between 20° C. and 70° C. to form a porous layer on a surface of a transition metal oxide and/or hydroxide on the substrate; and depositing a layer of a liquid-repellent compound onto the porous layer of the transition metal oxide and/or hydroxide to form the porous liquid-repellent coating on the substrate.
12. The method of claim 11 , wherein immersing the substrate comprises immersing the substrate in an equimolar solution of the transition metal nitrate salt and the weak base.
13. The method of claim 11 , wherein the solution of the transition metal nitrate salt and the weak base has a concentration of between 1 mM and 1 M.
14. The method of claim 11 , further comprising subjecting the porous layer of the transition metal oxide and/or hydroxide to a cleaning treatment prior to depositing the layer of the liquid-repellent compound.
15. The method of claim 11 , wherein the weak base comprises hexamethylenetetramine (HMTA), hexamine, triethanolamine, ammonia, or urea.
16. The method of claim 11 , wherein the substrate comprises aluminium and the transition metal nitrate salt comprises a transition metal selected from the group consisting of zinc, nickel, manganese, copper, cobalt, iron, and a mixture thereof.
17. The method of claim 16 , wherein the transition metal nitrate salt comprises zinc nitrate or manganese (II) nitrate.