Transparent and insulating materials having evacuated capsules

1. A method comprising:

forming a composition consisting essentially of a plurality of hollow spherical silica shells within a solution;

dispersing and suspending the hollow spherical silica shells within the solution such that a packing density of the hollow spherical silica shells within the solution is greater than 30%, and a visible light transmission of the solution is greater than 75%;

processing the solution with a sol-gel method; and

drying the processed solution to form a secondary shell of silica, wherein:

the hollow spherical silica shells are integrated by the secondary shell to form a layer consisting essentially of the hollow spherical silica shells and the secondary shell,

at least a portion of the hollow spherical silica shells have an internal volume at a pressure of less than 1 microtorr,

each hollow spherical silica shell has a lateral dimension between 50 nm and 300 nm,

the layer has a thickness between 3.175 mm and 6.35 mm,

the layer has a thermal conductivity between 0.001 W/m-K and 0.02 W/m-K, and

the layer has a visible light transmission of greater than 30% and less than 70%.

2. The method of claim 1 , wherein the dispersing and suspending comprises:

adjusting a pH of the solution to a value between 9 and 14, and

adding a polycation or a polyanion to the solution.

3. The method of claim 1 , wherein the packing density is greater than 70%.

4. The method of claim 1 , further comprising adding a strengthening agent to the solution before processing the solution.

5. The method of claim 4 , wherein the strengthening agent comprises at least one of poly(vinyl alcohol) or boric acid.

6. The method of claim 1 , wherein the forming comprises:

creating a template using dodecanethiol and cetyl-trimethylammonium bromide;

coating the template with a silica-gel; and

heating the template to a temperature of at least 250° C. in vacuum, resulting in the hollow spherical silica shells.

7. The method of claim 6 , wherein the forming further comprises performing atomic layer deposition, physical vapor deposition, chemical vapor deposition, or solution phase deposition to deposit a low-emissivity coating on the hollow silica shells.

8. The method of claim 1 , wherein each of the hollow spherical silica shells has a lateral dimension between 50 nm and 300 nm.

9. The method of claim 8 , wherein the lateral dimension is between 80 nm and 100 nm.

10. A composition comprising:

a layer consisting essentially of:

a plurality of hollow spherical primary silica shells; and

a secondary shell of silica integrated with the hollow spherical primary silica shells to form the layer, wherein:

each hollow spherical primary silica shell has a lateral dimension between 50 nm and 300 nm,

at least a portion of the hollow spherical primary silica shells have an internal volume at a pressure of less than 1 microtorr,

the layer has a thickness between 3.175 mm and 6.35 mm,

the layer has a thermal conductivity between 0.001 W/m-K and 0.02 W/m-K; and

the layer has a visible light transmission of greater than 30% and less than 70%.

11. The composition of claim 10 , wherein the lateral dimension is between 80 nm and 100 nm.

12. The composition of claim 10 , wherein at least a portion of the hollow spherical primary silica shells are concave.

13. The composition of claim 10 , wherein at least a portion of the hollow spherical primary silica shells has thickness between 3 nanometers and 20 nanometers.

14. The composition of claim 10 , wherein the secondary shell has a shape that is substantially cylindrical.

15. The composition of claim 10 , further comprising boric acid, wherein the boric acid strengthens the layer.

16. The composition of claim 10 , wherein at least a portion of the hollow spherical primary silica shells and the secondary shell form a pore.

17. The composition of claim 10 , wherein the secondary shell is produced by a sol-gel method.