Hydrophobic-core microcapsules and their formation

• US 9,233,394 B2
• Filed: 08/13/2010
• Issued: 01/12/2016
• Est. Priority Date: 09/19/2005
• Status: Active Grant

• Current Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Calle, Luz M., Li, Wenyan, Buhrow, Jerry W., Jolley, Scott T.
• Primary Examiner(s): LOUIE, MANDY C
• Application Number:
  US12/855,791
• Publication Number:
  US 20100305234A1
• Time in Patent Office: 1,978 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: B05D 2202/00 Metallic substrate
• CPC Class Codes: B05D 5/00 Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
• CPC Class Codes: B05D 5/06 to obtain multicolour or other optical effects B05D5/02 takes precedence
• CPC Class Codes: C08K 9/10 Encapsulated ingredients
• CPC Class Codes: C09D 5/082 characterised by the anti-corrosive pigment
• CPC Class Codes: C09D 5/29 for multicolour effects
• CPC Class Codes: C09D 7/41 Organic pigments; Organic dyes
• CPC Class Codes: C09D 7/48 Stabilisers against degradation by oxygen, light or heat
• CPC Class Codes: C09D 7/65 macromolecular C09D7/41-C09D7/48 take precedence
• CPC Class Codes: C09D 7/70 characterised by shape, e.g. fibres, flakes or microspheres
• CPC Class Codes: Y10T 428/2984 Microcapsule with fluid core [includes liposome]
• CPC Class Codes: Y10T 428/2985 Solid-walled microcapsule from synthetic polymer
• CPC Class Codes: Y10T 428/2987 Addition polymer from unsaturated monomers only
• CPC Class Codes: Y10T 428/2989 Microcapsule with solid core [includes liposome]
• CPC Class Codes: Y10T 428/2991 Coated
• CPC Class Codes: Y10T 428/2998 including synthetic resin or polymer

Abstract

Hydrophobic-core microcapsules and methods of their formation are provided. A hydrophobic-core microcapsule may include a shell that encapsulates a hydrophobic substance with a core substance, such as dye, corrosion indicator, corrosion inhibitor, and/or healing agent, dissolved or dispersed therein. The hydrophobic-core microcapsules may be formed from an emulsion having hydrophobic-phase droplets, e.g., containing the core substance and shell-forming compound, dispersed in a hydrophilic phase. The shells of the microcapsules may be capable of being broken down in response to being contacted by an alkali, e.g., produced during corrosion, contacting the shell.

Claims

1. A method of forming hydrophobic-core microcapsules comprising:

forming a hydrophobic phase including a pre-polymer or monomer, a cross-linking agent, at least one active substance, wherein said at least one active substance is a corrosion indicator, a corrosion inhibitor, or combination thereof, an optional co-solvent, and a hydrophobic substance;

forming a hydrophilic phase;

mixing the hydrophobic phase with the hydrophilic phase to create and disperse droplets of the hydrophobic phase within the hydrophilic phase to form an emulsion;

initiating a reaction at an interface of the hydrophilic phase and the hydrophobic phase to form a solid shell encapsulating the hydrophobic phase forming hydrophobic-core microcapsules, wherein said solid shell includes a shell wall comprising a compound having one or more chemical bonds that are broken down when contacted with an alkali produced during a corrosion reaction causing the release of the hydrophobic phase, wherein said alkali has a pH above about 8.

2. The method of claim 1, wherein said cross-linking agent comprises one or more ester groups.

3. The method of claim 2, wherein the cross-linking agent is selected from fully esterified monomers comprising ethyleneglycol di-2-mercapto acetate, ethyleneglycol di-2-hydroxyacetate, pentaerythritol tetrakis(2-hydroxyacetate), pentaerythritol tetrakis(3-hydroxypropionate), pentaerythritol tetrakis(2-mercaptoacetate), or pentaerythritol tetrakis(3-mercaptopropionate) or from any number of partially esterified polyols comprising glycerol monoacetate, neopentylglycol monopropionate, or trimethylolpropane diacetate.

4. The method of claim 2, wherein the pre-polymer or monomer is selected from the group consisting of urea formaldehyde, melamine formaldehyde and other amine formaldehyde prepolymers, polyurethane prepolymers, polyols, isocyanates, and other shell wall forming pre-polymers or monomers.

5. The method of claim 1, wherein forming the hydrophilic phase includes the further step of adding one or more surfactants to a hydrophilic substance.

6. The method of claim 1, including a further step of adding a catalyst to the emulsion.

7. The method of claim 6, wherein the catalyst is an acid.

8. The method of claim 1, including a further step of heating the emulsion.

9. The method of claim 8, including a further step of heating the emulsion to a temperature ranging from 50-70°

C. resulting in a reaction time of less than about 3 hours for solid-shell wall formation.

11. The method of claim 1 wherein said shell wall includes about 20 percent to about 50 percent, by mass, cross-linking agent and about 50 percent to about 80 percent, by mass, pre-polymer.

12. The method of claim 1, wherein said at least one active substance is a corrosion indicator that changes color over the alkaline region of pHs from about 8 to about 10.

13. The method of claim 12, wherein said corrosion indicator is phenolphthalein.

14. The method of claim 1, wherein said at least one active substance is a corrosion indicator that fluoresces in the presence of or upon the oxidation of metal or in the presence or upon the formation of a metal cation complex.

15. The method of claim 14, wherein said corrosion indicator is selected from the group consisting of 7-hydroxycoumarin, coumarin, and Rhodamine B.

16. The method of claim 1, wherein said at least one active substance is a corrosion inhibitor.

17. The method of claim 16, wherein said corrosion inhibitor is selected from the group consisting of sodium nitrate, camphor, polyamine fatty acid salts in a solvent, sodium molybdate, cerium nitrate, sodium phosphate, and calcium metaborate.

18. The method of claim 1, wherein said hydrophobic-core microcapsules have a typical size from about 1 to about 50 microns.

10. A method of forming hydrophobic-core microcapsules comprising:

forming a first hydrophobic phase including at least one active substance and at least one surfactant in the absence of a cross-linking agent and in the absence of a pre-polymer;

forming a hydrophilic phase;

mixing the first hydrophobic phase with the hydrophilic phase to form an emulsion comprising droplets of the first hydrophobic phase dispersed in the hydrophilic phase;

forming a second hydrophobic phase including a cross-linking agent comprising one or more ester groups and a pre-polymer in the absence of any active substance;

mixing the second hydrophobic phase to said emulsion to form droplets including the first hydrophobic phase and the second hydrophobic phase dispersed in the hydrophilic phase; and

initiating a reaction at an interface of the hydrophilic phase and droplets including the first and second hydrophobic phases to form a single shell encapsulating the first and second hydrophobic phases forming hydrophobic-core microcapsules, wherein said single shell includes a shell wall comprising a compound having one or more chemical bonds that are broken down when contacted with an alkali produced during a corrosion reaction causing the release of the first and second hydrophobic phases, wherein said alkali has a pH above about 8.

19. The method of claim 10 wherein said emulsion including the first hydrophobic phase and the second hydrophobic phase dispersed in the hydrophilic phase includes:

about 1 to about 15 percent, by mass, the first hydrophobic phase,

about 10 to about 20 percent, by mass, the second hydrophobic phase; and

about 65 to about 89 percent, by mass, the hydrophilic phase.

20. The method of claim 10 wherein said shell wall includes about 20 percent to about 50 percent, by mass, cross-linking agent and about 50 percent to about 80 percent, by mass, pre-polymer.

21. The method of claim 10, wherein said cross-linking agent comprises one or more ester groups.

22. The method of claim 10, wherein said at least one active substance is a corrosion indicator, a corrosion inhibitor, a film-forming compound, or combinations thereof.

23. The method of claim 10, including a further step of adding a catalyst to the emulsion.