Organically modified hybrid aerogels
View Patent ↗Disclosed and claimed herein are hybrid aerogels which are compositions of tetraalkoxysilanes and bis-(trialkoxysilyl)imides that exhibit low thermal conductivities and high compressive strengths. Methods for their preparation are also provided.
1. Hybrid aerogels comprising the reaction product of:
a. at least one tetraalkoxysilane which may optionally be partially hydrolyzed,
b. at least one bis-trialkoxysilane diimide, and
c. a selected amount of water;
wherein a gelation catalyst is admixed to gel the reaction product;
wherein the gel is dried to obtain an aerogel; and
wherein the at least one bis-trialkoxysilane diimide is a reaction product of: i) a primary amine terminated trialkoxysilane according to the following formula: H 2 N—R—Si—(OR′) 3 , wherein R comprises alkyl, alkenyl, alkynyl, cycloalkyl, or cycloalkenyl moities, or variations thereof which contain at least one heteroatom comprising O, S, N, P, or Se, and R′ is a C1-C21 branched or unbranched alkyl group; and ii) a dicarboxylic anhydride.
2. The hybrid aerogels of claim 1 , wherein the selected amount of water is calculated from a water to silicon ratio.
3. The hybrid aerogels of claim 2 , wherein the water to silicon ratios are between about 8 and about 20.
4. The hybrid aerogels of claim 1 , wherein the final density of the aerogel is about 0.7 grams/cubic centimeter or less.
5. The hybrid aerogels of claim 1 , wherein the final density of the aerogel is about 0.43 grams/cubic centimeter or less.
6. The hybrid aerogels of claim 1 , wherein the thermal conductivity of the aerogel is about 30 milliwatts/meter-degree Kelvin or less.
7. The hybrid aerogels of claim 1 , wherein the thermal conductivity of the aerogel is about 25 milliwatts/meter-degree Kelvin or less.
8. The hybrid aerogels of claim 1 , wherein the compressive modulus of the aerogel is greater than about 175 pounds/square inch.
9. The hybrid aerogels of claim 1 , wherein the diimide content of the aerogel is 25 wt % or less.
10. The hybrid aerogels of claim 1 , wherein the diimide content of the aerogel is 10 wt % or less.
11. The hybrid aerogels of claim 1 , wherein the diimide content of the aerogel is 25 wt % or less, and the compressive modulus of the aerogel is greater than about 175 pounds/square inch.
12. The hybrid aerogels of claim 1 , wherein the diimide content of the aerogel is 10 wt % or less, and the compressive modulus of the aerogel is greater than about 175 pounds/square inch.
13. The hybrid aerogels of claim 1 , wherein the at least one tetraalkoxysilane is partially hydrolyzed tetraalkoxysilane.
14. The hybrid aerogels of claim 1 , further comprising a fibrous material, comprising microfibers, mats, felts, woven fabrics, non-woven fabrics, fibrous battings, lofty battings or a combination thereof.
15. The method of claim 14 , further comprising an aging step after the gelation step, comprising contacting the siloxanes with an amine containing material.
16. A method of producing hybrid aerogels comprising:
a. combining at least one tetraalkoxysilane or optionally at least one partially hydrolyzed tetraalkoxysilane, at least one bis-trialkoxysilane diimide, and a selected amount of water, to form a reaction product;
b. admixing a gelation catalyst to gel the reaction product; and
c. drying the gel to obtain an aerogel;
wherein the at least one bis-trialkoxysilane diimide is a reaction product of: i) a primary amine terminated trialkoxysilane according to the following formula: H 2 N—R—Si—(OR′) 3 , wherein R comprises alkyl, alkenyl, alkynyl, cycloalkyl, or cycloalkenyl moities, or variations thereof which contain at least one heteroatom comprising O, S, N, P, or Se, and R′ is a C1-C21 branched or unbranched alkyl group; and ii) a dicarboxylic anhydride.
17. The method of claim 16 , wherein the selected amount of water is calculated from a water to silicon ratio.
18. The method of claim 16 , wherein the water to silicon ratios are between about 8 and about 20.
19. The method of claim 18 , wherein the final density of the aerogel is less than about 0.43 grams/cubic centimeter.
20. The method of claim 18 , wherein the thermal conductivity of the aerogel is less than about 30 milliwatts/meter-degree Kelvin or below.
21. The method of claim 18 , wherein the compressive modulus of the aerogel is greater than about 175 pounds/square inch.
22. The method of claim 18 , wherein the diimide content of the aerogel is 25 wt % or less.
23. The method of claim 18 , wherein the diimide content of the aerogel is 10 wt % or less.
24. The method of claim 18 , wherein the diimide content of the aerogel is 25 wt % or less, and the compressive modulus of the aerogel is greater than about 175 pounds/square inch.
25. The method of claim 18 , wherein the diimide content of the aerogel is 10 wt % or less, and the compressive modulus of the aerogel is greater than about 175 pounds/square inch.