Plasma treatment of substrates prior to the formation a self-assembled monolayer
An improved method for forming a self-assembled monolayer on a substrate is disclosed. The method comprises plasma treatment of the substrate prior to formation of the self-assembled monolayer.
1. A method for cleaning the surface of a metal substrate having metal oxide groups on the surface, comprising:
(a) treating the surface of the metal substrate with a plasma generated from a gas containing oxygen so as to generate metal oxide groups on the surface of the metal substrate and to remove contaminants from the surface of the metal substrate as gaseous reaction products,
(b) applying a solution or dispersion of a perfluorinated organo phosphorus acid of the structure:
where A is an oxygen radical or a chemical bond; n is 1 to 6; Y is H, F, C n F 2n+1 or C n H 2n+1 ; Z is H or F; b is 2 to 20; m is 0 to 6; p is 2 to 4; and X is a group selected from the group consisting of phosphoric acid, phosphinic acid and phosphonic acid, in a diluent to the surface of the metal substrate treated in step (a),
(c) removing the diluent, and
(d) forming a self-assembled organo phosphorus monolayer with the acid groups of the perfluorinated organo phosphorus acid covalently bonded to the metal surface by reaction with the oxide groups.
2. The method of claim 1 in which the plasma is generated at atmospheric pressure.
3. The method of claim 1 in which the plasma is created with radio frequency (Rf) energy.
4. The method of claim 1 in which the plasma is generated from air.
5. The method of claim 1 in which the solution or dispersion is heated to 30-200° C. prior to application to the substrate.
6. The method of claim 1 in which a subsequent coating is applied after formation of the self-assembled monolayer.
7. The method of claim 6 in which the subsequent coating contains perfluorinated polymer.
8. The method of claim 1 in which the substrate is a metal selected from iron or an iron alloy substrate.
9. The method of claim 8 in which the iron substrate is stainless steel.
10. The method of claim 1 in which the substrate is a metal selected from the group consisting of copper, aluminum, gold, palladium, silver, platinum, nickel, chromium, or tungsten and their alloys.
11. The method of claim 10 in which the metal substrate is aluminum or an aluminum alloy.
12. The method of claim 11 in which the metal substrate is a zinc-aluminum alloy.