Organic aerogel microspheres and fabrication method therefor

• US 5,508,341 A
• Filed: 07/08/1993
• Issued: 04/16/1996
• Est. Priority Date: 07/08/1993
• Status: Expired due to Term

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Pekala, Richard W., Mayer, Steven T., Kaschmitter, James L., Kong, Fung-Ming
• Primary Examiner(s): Michl, Paul R.
• Assistant Examiner(s): Guarriello, John J.
• Application Number:
  US08/089,119
• Time in Patent Office: 1,013 Days
• Field of Search: 524/596, 523/336, 523/337, 523/339, 521/181
• US Class Current: 524/596
• CPC Class Codes: B01J 13/00 Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
• CPC Class Codes: B01J 13/0091 Preparation of aerogels, e.g. xerogels
• CPC Class Codes: H01G 11/26 characterised by their structure, e.g. multi-layered, porosity or surface features
• CPC Class Codes: H01G 11/42 Powders or particles, e.g. composition thereof
• CPC Class Codes: H01G 11/70 characterised by their structure
• CPC Class Codes: Y02E 60/13 Energy storage using capacitors
• CPC Class Codes: Y10T 428/2982 Particulate matter [e.g., sphere, flake, etc.]

Abstract

Organic aerogel microspheres which can be used in capacitors, batteries, thermal insulation, adsorption/filtration media, and chromatographic packings, having diameters ranging from about 1 micron to about 3 mm. The microspheres can be pyrolyzed to form carbon aerogel microspheres. This method involves stirring the aqueous organic phase in mineral oil at elevated temperature until the dispersed organic phase polymerizes and forms nonsticky gel spheres. The size of the microspheres depends on the collision rate of the liquid droplets and the reaction rate of the monomers from which the aqueous solution is formed. The collision rate is governed by the volume ratio of the aqueous solution to the mineral oil and the shear rate, while the reaction rate is governed by the chemical formulation and the curing temperature.

Claims

1. A method for fabricating organic aerogel microspheres, comprising:

mixing an aqueous reactant phase solution containing a multifunctional monomer with a non-miscible solvent;

agitating the thus formed mixture until the aqueous phase of the mixture polymerizes and forms gel spheres;

curing the thus formed gel spheres; and

drying the thus cured gel spheres thereby forming aerogel microspheres.

2. The method of claim 1, additionally including the steps of:

removing air bubbles from the mixture prior to agitating the mixture; and

washing the cured gel spheres after curing same.

3. The method of claim 1, wherein the step of agitating the mixture is carried out by heating and stirring the mixture.

4. The method of claim 1, wherein the step of washing includes, washing with a cleaning agent to remove the non-miscible solvent, and then exchanging with a solvent to remove water from the cured gel spheres.

5. The method of claim 1, additionally including the step of adding a surfactant to the solution.

6. The method of claim 2, additionally including the step of pyrolyzing the aerogel microspheres in an atmosphere selected from the group consisting of inert atmospheres for forming carbon aerogel microspheres and oxidizing atmospheres for forming activated carbon aerogel microspheres.

7. The method of claim 1, additionally including the step of doping the gel spheres.

8. The method of claim 1, additionally including the step of forming the aqueous solution from selected reactant combinations, a catalyst, and with or without distilled, deionized water.

9. The method of claim 8, wherein the reactant combinations is selected from the group including resorcinol/formaldehyde, melamine/formaldehyde, resorcinol/furfural, phenol-resorcinol/formaldehyde, catechol/formaldehyde, and phloroglucinol/formaldehyde.

10. The method of claim 9, wherein the catalyst is sodium carbonate.

11. The method of claim 2, wherein the step of washing is carried out in a solvent selected from the group consisting of toluene, acetone, and cyclohexane.

12. The method of claim 11, wherein the solvent is cyclohexane.

13. The method of claim 11, wherein the steps of washing and exchanging are first carried out in toluene and then in acetone.

14. The method of claim 1, additionally including the step of forming the aqueous solution by mixing resorcinol, formaldehyde, sodium carbonate, and distilled and deionized water.

15. The method of claim 14, wherein the aqueous solution is formed from reactants with a concentration of about 3-70% w/v.

16. The method of claim 14, wherein the non-miscible solvent is selected from the group consisting of moderate to long chain saturated hydrocarbons, and long chain alcohols.

17. The method of claim 16, wherein the non-miscible solvent is mineral oil.

18. The method of claim 17, wherein the step of heating and stirring is carried out by stirring at a temperature of 20°

-100°

C. for a time period of at least 10 minutes.

19. The method of claim 18, wherein the step of heating and stirring is continued for a time period after the gel point passes.

20. The method of claim 19, wherein the step of curing the gel spheres is carried out in mineral oil at a temperature of about 20°

C. to about 95°

C. for a time period of about 1 hour to 3 days.

21. The method of claim 20, wherein the step of washing the cured gel spheres is carried out by first washing in toluene for a specified time period, and then in acetone for a specified time period.

22. The method of claim 21, wherein the step of drying the washed gel spheres is carried out by the process selected from the group of supercritical drying with carbon dioxide, and low pressure and/or evaporative drying.

38. The method of claim 14, wherein the non-miscible solvent is cyclohexane.

23. A method for producing organic aerogel microspheres having a diameter in the range of 1-1000 μ

m comprising the steps of;

forming an aqueous solution containing at least reactants including a monomer and a catalyst;

mixing the thus formed aqueous solution with an excess of a non-polar, water insoluble solvent;

stirring the thus formed mixture so as to form an emulsion with continuous oil phase, and forming microspheres in a non-continuous aqueous droplet phase;

continuing stirring for a period of time so that the microspheres are hardened;

washing the microspheres with a solvent and concurrently exchanging water in the aquagel microspheres with the solvent; and

exchanging the solvent with liquid carbon dioxide via extraction of the solvent with the carbon dioxide to produce solvent-free aerogel microspheres.

24. The method of claim 23, additionally including the step of pyrolyzing the aerogel microspheres in either an inert or oxidizing atmosphere to form carbon aerogel microspheres.

25. The method of claim 23, wherein the step of forming the aqueous solution is carried out by mixing at least a reactant composed of polyhydroxy-benzene compounds selected from the group consisting of resorcinol, phenol, catechol, and phloroglucinol, with either formaldehyde or furfural in a predetermined ratio and in the presence of a base catalyst.

26. The method of claim 25, wherein the step of forming the aqueous solution is carried out by mixing resorcinol, formaldehyde, deionized water, and 0.1M sodium carbonate.

27. The method of claim 26, wherein the aqueous solution is formed so as to be composed of 12.35 grams of resorcinol, 17.92 grams of formaldehyde, 13.9 grams of deionized water, and 22.32 grams of 0.1M sodium carbonate.

28. The method of claim 26, wherein the aqueous solution is formed to have a 2:

1 molar ratio of formaldehyde to resorcinol and a 30% w/v fraction of reactants.

29. The method of claim 28, wherein the aqueous solution is formed such that the reactant to catalyst ratio (R/C) equals at least 50.

30. The method of claim 23, wherein the non-polar, water insoluble solvent is selected from the group consisting of moderate to long chain saturated hydrocarbons, and long chain alcohols.

31. The method of claim 23, additionally including the step of adding an emulsion stabilizer to the thus formed mixture.

32. The method of claim 23, additionally including the step of filtering the thus formed aquagel microspheres.

39. The method of claim 23, wherein the non-polar, water insoluble solvent is mineral oil.

40. The method of claim 23, wherein the non-polar, water insoluble solvent is cyclohexane.

33. A method of producing resorcinol/formaldehyde carbon aerogel microspheres, comprising the steps of:

mixing resorcinol, formaldehyde, deionized water and 0.1M sodium carbonate to form an aqueous solution of a 2;

1 molar ratio of formaldehyde to resorcinol and a 30% weight/volume fraction of reactants;

mixing the aqueous solution with an excess of a non-polar, water insoluble solvent selected from the group of mineral oil, cyclohexane, saturated hydrocarbons, and p-xylene;

adding to the mixture a surfactant;

stirring the mixture vigorously for forming an inverse emulsion with the oil phase being continuous and the RF aquagel forming in a non-continuous aqueous droplet phase;

continuing stirring for a period of about 5 hours causing the aqueous droplets to harden producing microspheres;

filtering and washing the RF microspheres with acetone to remove the oil phase and concurrently exchange the water therein with acetone;

exchanging the acetone with liquid carbon dioxide via a supercritical extraction or a non-supercritical extraction technique to produce RF aerogel microspheres; and

firing the RF aerogel microspheres in an inert or oxidizing atmosphere to form carbon aerogel microspheres.

34. A method for fabricating organic aerogel microspheres by inverse emulsion polymerization, wherein the size of the microspheres is determined by the processing procedures and the chemical formulation, comprising the steps of:

mixing selected reactants including a monomer with at least a catalyst to form an aqueous solution;

mixing the thus formed aqueous solution with a non-miscible solvent forming an inverse emulsion;

heating the thus formed mixture to a temperature in the range of 20°

-100°

C.;

stirring the heated mixture to form a colloidal suspension of aqueous phase droplets in a continuous oil phase;

continuing stirring of the heated mixture until the aqueous phase undergoes gelation and microspheres are formed;

removing the oil phase from the surface of the thus formed microspheres;

removing water from within the thus formed microspheres; and

drying the thus formed microspheres.

35. The method of claim 34, additionally including the step of pyrolyzing the microspheres in an inert atmosphere to form carbon aerogel foam microspheres.

36. The method of claim 34, additionally including the step of pyrolyzing the microspheres in an oxidizing atmosphere to form activated carbon microspheres having a higher surface area than microspheres pyrolyzed in an inert atmosphere.

37. The method of claim 34, additionally including the step of determining the size of the microspheres by:

establishing the collision rate of the liquid droplets by controlling the volume ratio of the aqueous solution to the oil phase, and the shear rate; and

establishing the reaction rate of the monomers from which the aqueous solution is formed by controlling the chemical formulation of the aqueous solution and the curing temperature.