Surface-modified zinc oxide for the production of nanoparticulate dispersions
The present invention relates to a surface-modified nanoscale zinc oxide, where the surface modification involves coating with an oligo- or polyethylene glycol acid. This surface-modified zinc oxide is characterized in that it forms stable dispersions in a liquid medium. In addition, the present invention relates to a process for the production of surface-modified zinc oxide, and also to a process for the production of nanoscale zinc oxide dispersions.
1. A composition comprising:
particles of zinc oxide coated with an oligo- or polyethylene glycol acid; and
a solvent with a dipole moment greater than 0.35 μ/D.
2. The composition of claim 1 , wherein the zinc oxide particles have a diameter of 1-200 nm.
3. The composition of claim 1 , wherein the zinc oxide particles have a diameter of 2-50 nm.
4. The composition of claim 1 , wherein the oligo- or polyethylene glycol acid has a formula:
R—CH 2 —(O—CH 2 —CH 2 ) n —O—CH 2 —COOH
wherein:
n is an integer from 0 to 40; and
R is H, CH 3 , C 2 H 5 , C 3 H 7 , CH(CH 3 ) 2 , OH, NH 2 , COOH, CONH 2 , CO 2 CH 3 , CO 2 C 2 H 5 , CO 2 C 3 H 7 or CO 2 CH(CH 3 ) 2 .
5. The composition of claim 4 , wherein R is COOH.
6. The composition of claim 1 , wherein the oligo- or polyethylene glycol acid is polyethylene glycol diacid 600.
7. The composition of claim 1 , wherein the oligo- or polyethylene glycol acid is 2-[2-(2-methoxyethoxy)ethoxy]acetic acid.
8. The composition of claim 1 , wherein the composition forms stable dispersions.
9. The composition of claim 8 , wherein the composition is redispersible in polar organic solvents or water.
10. A method for making zinc oxide redispersible in polar organic solvents or water, comprising:
suspending zinc oxide in a solvent with a dipole moment greater than 0.35 μ/D; and
adding an oligo- or polyethylene glycol acid to form particles of zinc oxide coated with an oligo- or polyethylene glycol acid.
11. The method of claim 10 , wherein the solvent is an organic solvent.
12. The method of claim 11 , wherein the organic solvent is at least one of methanol, ethanol, n-propanol, isopropanol, acetone, diethyl ether, dimethyl sulfoxide, tetrahydrofuran, methylene chloride, trichloromethane, ethanol, ethyl acetate, isobutyl acetate or toluene.
13. The method of claim 10 , wherein the solvent is THF.
14. The method of claim 10 , wherein the solvent is a polar solvent.
15. The method of claim 10 , further comprising heating during the step of adding.
16. The method of claim 10 , further comprising drying the particles.
17. The method of claim 10 , further comprising removing the solvent by evaporation, freezing, freeze-drying, filtering, or drying.
18. A zinc oxide dispersion, comprising the composition of claim 1 .
19. The zinc oxide dispersion of claim 18 , wherein the dispersion has a content of dispersed zinc oxide of from 0.001 to 50% by weight.
20. The zinc oxide dispersion of claim 18 , wherein the dispersion has a content of dispersed zinc oxide of from 0.1 to 10% by weight.
21. The zinc oxide dispersion of claim 18 , wherein the dispersion is largely transparent.