Hydrophobic aerogels comprising low occupancy of monofunctional units

Patent metadata

Field	Value
Publication number	US-10759666-B2
Application number	US-201615564334-A
Country	US
Kind code	B2
Filing date	Apr 21, 2016
Priority date	Apr 29, 2015
Publication date	Sep 1, 2020
Grant date	Sep 1, 2020

Abstract

The problem addressed by the invention is that of producing aerogels which have as high and permanent a hydrophobicity as possible and which have a reduced combustibility, that is as low a carbon content as possible, and are simultaneously less rigid and brittle than known systems, i.e. which with reduced combustibility have a high flexibility and high stability at the same time, that is high mechanical load-bearing capacity. Said problem is solved in that the invention provides gels chosen from lyogel or aerogel, which are synthesised from oxide units and [RxSiO(4-x)/2] units, wherein the primary particles have a change of concentration in [RxSiO(4-x)/2] units from the inside to the outside, wherein x can be the same or different and is 1 or 2, and R can be the same or different and is hydrogen or an organic substituted or unsubstituted radical, and wherein the oxide units contain [SiO4/2] units, and a method for producing same. The gels provided can be used in cosmetic, medical or for chromatographic applications, and as a catalyst or catalyst support. If the gels are aerogels, same are preferably used for thermal and/or acoustic insulation.

First claim

The invention claimed is:

1. A gel comprising lyogel- or aerogel-containing primary particles comprising oxidic units and [R x SiO (4-x)/2 ] units, wherein
the primary particles have an increase in a concentration of [R x SiO (4-x)/2 ] units from inside to outside,
indices x can be identical or different and are in each case 1 or 2,
radicals R can be identical or different and are each hydrogen or an organic, substituted or unsubstituted radical,
interparticular linkages of the primary particles comprise [R x SiO (4-x)/2 ] units, and
the oxidic units contain [SiO 4/2 ] units.

2. The gel as claimed in claim 1 , wherein the primary particles are built up in a form of a core-shell model, where a core contains a concentration of [R x SiO (4-x)/2 ] units of less than 20 mol % and a shell contains a concentration of [R x SiO (4-x)/2 ] units of more than 80 mol %.

3. The gel as claimed in claim 1 , wherein the radical R is a methyl group.

4. The gel as claimed in claim 1 , wherein a degree of coverage with monofunctional units on a surface is less than 1.5 groups per nm 2 .

5. The gel as claimed in claim 1 , which is an aerogel having a density of less than 0.25 g/cm 3 .

6. The gel as claimed in claim 1 , which is an aerogel having a carbon content of less than 15% by weight.

7. The gel as claimed in claim 1 , which is an aerogel having a density of less than 0.15 g/cm 3 , a degree of coverage with monofunctional units of not more than 1 per nm 2 , a carbon content of not more than 8% by weight and a BET surface area of greater than 300 m 2 /g.

8. The gel as claimed in claim 1 , wherein only [SiO 4/2 ] units are present as oxidic units.

9. A process for producing gels of claim 1 , comprising:
i) placing a sol containing colloidal particles, where the colloidal particles contain oxidic units, in a reaction vessel, where the oxidic units contain [SiO 4/2 ] units and the sols are produced by neutralization of strongly basic alkali metal silicates or by hydrolysis of alkoxysilanes,
ii) reacting the particles in the sol with [R x SiO (4-x)/2 ] units, where the indices x can be identical or different and are in each case 1 or 2 and the radicals R can be identical or different and are each hydrogen or an organic, substituted or unsubstituted radical,
iii) and forming a gel from the sol.

10. The process as claimed in claim 9 , wherein solutions of colloidal particles containing [SiO 4/2 ] units are used as a starting material, where the particles have an average diameter in a range from 1 to 8 nm.

11. The process as claimed in claim 9 , wherein the gel is covered with monofunctional units by surface modification.

12. The process as claimed in claim 9 , wherein the gel is dried.

13. The gel as claimed in claim 1 , which is an aerogel effective for thermal and/or acoustic insulation.

14. The gel as claimed in claim 1 , which is effective for cosmetic, medical or chromatographic applications or as catalysts or catalyst supports.

15. The gel as claimed in claim 1 , wherein the primary particles are built up in a form of a core-shell model, where a core contains a concentration of [R x SiO (4-x)/2 ] units of less than 20 mol % and a shell contains a concentration of [R x SiO (4-x)/2 ] units of more than 80 mol %.

16. The gel as claimed in claim 15 , wherein the radical R is a methyl group.

17. The gel as claimed in claim 16 , wherein a degree of coverage with monofunctional units on a surface is less than 1.5 groups per nm 2 .

18. The gel as claimed in claim 17 , which is an aerogel having a density of less than 0.25 g/cm 3 .

19. The gel as claimed in claim 18 , which is an aerogel having a carbon content of less than 15% by weight.

20. The gel as claimed in claim 19 , which is an aerogel having a density of less than 0.15 g/cm 3 , a degree of coverage with monofunctional units of not more than 1 per nm 2 , a carbon content of not more than 8% by weight and a BET surface area of greater than 300 m 2 /g.

21. The gel as claimed in claim 20 , wherein only [SiO 4/2 ] units are present as oxidic units.

22. A process for producing gels of claim 20 , comprising:
i) placing a sol containing colloidal particles, where the colloidal particles contain oxidic units, in a reaction vessel, where the oxidic units contain [SiO 4/2 ] units and the sols are produced by neutralization of strongly basic alkali metal silicates or by hydrolysis of alkoxysilanes,
ii) reacting the particles in the sol with [R x SiO (4-x)/2 ] units, where the indices x can be identical or different and are in each case 1 or 2 and the radicals R can be identical or different and are each hydrogen or an organic, substituted or unsubstituted radical,
iii) and forming a gel from the sol.

23. The process as claimed in claim 22 , wherein solutions of colloidal particles containing [SiO 4/2 ] units are used as a starting material, where the particles have an average diameter in a range from 1 to 8 nm.

24. The process as claimed in claim 23 , wherein the gel is covered with monofunctional units by surface modification.

25. The process as claimed in claim 24 , wherein the gel is dried.

26. The gel as claimed in claim 21 , which is an aerogel effective for thermal and/or acoustic insulation.

27. The gel as claimed in claim 21 , which is effective for cosmetic, medical or chromatographic applications or as catalysts or catalyst supports.

Assignees

• Wacker Chemie Ag

Inventors

• Hindelang Konrad
• Jantke Dominik
• Weidner Richard

Classifications

• B01J35/45

  Nanoparticles · CPC title

• B01J35/23

  in a colloidal state · CPC title

• C01P2006/90

  Other properties not specified above · CPC title

• C01P2006/12

  Surface area · CPC title

• C01P2006/10

  Solid density · CPC title