Antifouling coatings and methods for coating substrates
Coatings for reducing or preventing fouling of surfaces are provided. In some embodiments, the coating comprises a silane compound, a siloxane compound, a phosphonate compound, a silicone polymer such as PDMS (polydimethylsiloxane), or a combination of silane-siloxane-phosphonate-PDMS in various molecular configurations in single monolayer and overlay assemblies. Also provided are related methods for forming the coating as well as coated substrates such as heat exchangers. Embodiments of the coatings are highly hydrophobic with high contact angles and the coated substrates may be used in a variety of industrial applications that require handling of oil-in-water emulsions, process water and produced water from various process operations, including Steam Assisted Gravity Drainage (SAGD) operations.
1 . A method for forming a coating on a surface of a substrate, comprising:
cleaning the surface of the substrate;
providing a coating composition comprising at least one surface modifying compound, the at least one surface modifying compound comprising an alkyl silane, a siloxane, an alkyl-phosphonic acid, or a combination thereof,
contacting the surface of the substrate with the coating composition such that at least a portion of the surface modifying compound is grafted to the surface to form a coated surface;
heat treating the coated surface at a first temperature for a first time period;
heat treating the coated surface at a second temperature for a second time period, the second temperature being higher than the first temperature;
heat treating the coated surface at a third temperature for a third time period, the third temperature being higher than the second temperature; and
repeating the contacting and heat treating steps at least one additional time.
2 . The method of claim 1 , wherein the surface modifying compound comprises the siloxane and wherein the siloxane has formula (I):
wherein R 1 is an alkyl group, R 2 is hydrogen (—H), hydroxyl (—OH), an alkoxy group (O-alkyl), or another reactive group, and n is the degree of polymerization; and
wherein R 1 is optionally partially or fully fluorinated or partially or fully hydrogenated.
3 . The method of claim 1 , wherein the surface modifying compound comprises the alkyl-phosphonic acid and wherein the alkyl-phosphonic acid has formula (III):
wherein R 6 is an alkyl group; and
wherein R 6 is optionally partially or fully fluorinated or partially or fully hydrogenated.
4 . The method of claim 1 , wherein the surface modifying compound comprises the alkyl silane and the alkyl silane has formula (II):
wherein R 1 is an alkyl group and each of R 3 , R 4 , and R 5 are independently selected from —H and an alkyl group; and
wherein R 1 is optionally partially or fully fluorinated or partially or fully hydrogenated.
5 . The method of claim 1 , wherein the surface modifying compound comprises the alkyl-phosphonic acid, and wherein the method further comprises:
providing a silicone coating composition comprising a polydimethylsiloxane (PDMS) base polymer and a cross-linking compound;
contacting the coated surface with the silicone coating composition to form a silicone-coated surface; and
heat treating the silicone-coated surface at between about 60° C. and about 100° C. for between about 12 hours and about 20 hours, followed by a second heat treatment at between about 100° C. and about 140° C. for 30 minutes and 4 hours.
6 . The method of claim 5 , wherein the PDMS base polymer has formula (VI):
wherein R 7 and R 8 are independently selected alkyl groups and n is the degree of polymerization;
wherein the cross-linking compound has formula (VII):
wherein R 9 is an alkyl group partially substituted with —H and n is the degree of polymerization; and
wherein R 7 , R 8 , and R 9 are optionally partially or fully fluorinated or partially or fully hydrogenated.
7 . The method of claim 5 , further comprising contacting the silicone-coated surface with another coating composition comprising alkyl-phosphonic acid followed by heat treating at the first temperature for the first time period, the second temperature for the second time period, and the third temperature for the third time period.
8 . The method of claim 1 , wherein:
the first temperature is between about 40° C. and about 100° C. and the first time period is between about 30 minutes and 2 hours;
the second temperature is between about 100° C. and about 160° C. and the second time period is between about 1 hour and 3 hours; and
the third temperature is between about 110° C. and about 180° C. and the third time period is between about 30 minutes and 2 hours.
9 . The method of claim 1 , wherein the substrate is at least a portion of a heat exchanger and the surface is a heat exchange surface.
10 . The method of claim 9 , wherein the cleaning, contacting, and heat treating steps are each performed in situ.
11 . The method of claim 10 , wherein at least one of the heat treating steps comprises contacting the coated surface with a heated inert gas or vapor within the heat exchanger, or passing a heated inert gas, vapor, or liquid through the heat exchanger on an opposite side of the coated surface.
12 . The method of claim 1 , wherein the cleaning step comprises:
contacting the surface with a first organic solvent;
contacting the surface with a second organic solvent;
contacting the surface with a diluted organic solvent in water; and
contacting the surface with pure water.
13 . A method for forming a coating on at least one heat exchange surface of a heat exchanger, comprising:
cleaning the heat exchange surface by passing at least one cleaning fluid through the heat exchanger;
providing a coating composition comprising at least one surface modifying compound, the at least one surface modifying compound comprising a silane, a siloxane, an alkyl-phosphonic acid, or a combination thereof;
introducing the coating composition into the heat exchanger such that the coating composition contacts the at least one heat exchange surface to form a coated surface; and
heat treating the coated surface by passing a heating medium through the heat exchanger.
14 . The method of claim 13 , wherein the heating medium is a heated inert gas or vapor and wherein the heating medium directly contacts the coated surface.
15 . The method of claim 13 , wherein the heating medium is a heated liquid, gas, or vapor and wherein the heating medium indirectly heats the coated surface by passing through the opposite side of the coated surface.
16 . The method of claim 13 , wherein heat treating the coated surface comprises:
passing the heating medium through the heat exchanger at a first temperature for a first time period;
passing the heating medium through the heat exchanger at a second temperature for a second time period, the second temperature being higher than the first temperature; and
passing the heating medium through the heat exchanger at a third temperature for a third time period, the third temperature being higher than the second temperature.
17 . The method of claim 13 , further comprising introducing a silicone coating composition into the heat exchanger to contact the coated surface and form a silicone-coated surface, followed by heat treating the silicone-coated surface.