Optical element comprising a crack-free aerogel
View Patent ↗A method manufactures an optical element having a surface that includes cells filled with an aerogel that does not crack during its manufacture or during a subsequent step of impregnating the aerogel with a liquid. The disclosure also relates to the optical elements that can be obtained using the method.
1. A process for manufacturing a transparent optical element comprising:
a) providing an optical element having a surface with at least one open cell;
b) carrying out a surface treatment of said cell, the surface treatment increasing the wettability of the surface;
c) preparing a solution comprising:
an organic-aqueous solvent;
at least one organic polymer, soluble in said solvent, having a weight-average molecular weight greater than 10,000 g/mol;
at least one alkoxysilane selected from the group consisting of (C 1 to C 3 alkyl)tri(C 1 to C 3 alkoxy)silanes and tetra(C 1 to C 3 alkoxy)silanes and mixtures thereof;
d) adding an acid or base hydrolysis catalyst to the solution so as to obtain a sol;
e) depositing the sol in the pretreated cell before the gel point of the sol is achieved and sealing the filled cell using a film;
f) leaving the optical element to stand in an alcoholic atmosphere for between 15 minutes and 5 hours in order to mature the gel;
g) removing the film sealing the cell in an alcoholic medium;
h) carrying out, in an autoclave, supercritical drying of the gel contained in the cell so as to obtain an aerogel.
2. The process as claimed in claim 1 , wherein the optical element, comprises several open cells on the surface of this optical element, the cells having a largest dimension between 10 and 10,000 μm.
3. The process as claimed in claim 1 , wherein the surface treatment carried out in step b) is performed with a low-pressure oxygen plasma.
4. The process as claimed in claim 1 , wherein the polymer included in the solution is selected from the group consisting of polyvinyl acetate, polyvinyl alcohol, poly(vinyl acetate-co-vinyl alcohol) copolymers; polyoxyethylene, polyoxypropylene and mixtures thereof.
5. The process as claimed in claim 1 , wherein the alkoxysilane included in the solution is tetramethoxysilane.
6. The process as claimed in claim 1 , wherein the sol obtained at the end of step d) comprises:
from 0.5% to 20% by weight, of polyvinyl acetate,
from 20% to 60% by weight of tetramethoxysilane,
the solvent consisting of a water/ethanol mixture.
7. The process as claimed in claim 1 , wherein the sol obtained at the end of step d) also comprises an additive selected from colloidal silica particles and conductive particles.
8. The process as claimed in claim 7 , wherein said conductive particles are selected from indium tin oxide (ITO) particles, tin oxide particles and metal particles.
9. The process as claimed in claim 1 , wherein the drying step h) is carried out with supercritical CO 2 .
10. The process as claimed in claim 1 , further comprising a step i) of, after the supercritical drying step h), purging the autoclave with an anhydrous gas, before removing the optical element.
11. The process as claimed in claim 1 , further comprising a step i) of placing the optical element obtained after step h) into a chamber having a controlled humidity.
12. A process for impregnating the optical element obtained by the process as claimed in claim 1 , comprising impregnating the aerogel contained in the at least one cell of the optical element with a liquid, then sealing the impregnated cell with a sealant that isolates and protects contents of the cell from the external atmosphere.