Method of forming aqueous-based dispersions of metal nanoparticles
View Patent ↗The invention relates to a method for preparing an aqueous-based dispersion of metal nanoparticles comprising: (a) providing an aqueous suspension of a metal salt; (b) pre-reducing the metal salt suspension by a water soluble polymer capable of metal reduction to form a metal nuclei; and (c) adding a chemical reducer to form metal nanoparticles in dispersion. The invention further relates to aqueous-based dispersions of metal nanoparticles, and to compositions such as ink comprising such dispersions.
1. A method for preparing an aqueous-based dispersion of metal nanoparticles comprising:
(a) providing an aqueous suspension of a metal salt;
(b) pre-reducing said metal salt suspension by a water soluble polymer capable of metal reduction to form metal nuclei; and
(c) adding a chemical reducer to form metal nanoparticles in dispersion.
2. The method of claim 1 further comprising at least one step of separating the nanoparticles obtained in step (c) from the aqueous medium of said dispersion and redispersing in a liquid to form a dispersion of nanoparticles.
3. The method of claim 2 wherein said separation is selected from centrifugation, decantation, filtration, ultrafiltration, and a combination thereof.
4. The method of claim 2 , wherein said redispersing involves the addition of a suitable dispersing agent and optionally a wetting agent.
5. The method of claim 4 wherein said dispersing agent is selected from surfactants, water soluble polymers, and mixtures of any of the above.
6. The method of claim 5 wherein said water soluble polymer is a polyelectrolyte.
7. The method of claim 4 wherein said wetting agent is a surfactant.
8. The method of claim 2 wherein said liquid is an aqueous liquid.
9. The method of claim 2 wherein the concentration of said metal nanopraticles in said dispersion is in the range 5-80 wt %, based on the total weight of the dispersion.
10. The method of claim 1 further comprising at least one step of separating the nanoparticles obtained in step (c) from the aqueous medium of said dispersion followed by removal of water in order to obtain a powder of metallic particles.
11. The method of claim 1 wherein said step (b) includes incubation for a period of at least 5 minutes.
12. The method of claim 1 , wherein step (b) is conducted at a temperature range of 20-100° C.
13. The method of claim 1 , wherein step (c) is conducted at a temperature range of 20-100° C.
14. The method of claim 1 wherein said metal nanoparticles are selected from silver nanoparticles, gold nanoparticles, platinum nanoparticles, palladium nanoparticles, and a mixture of any of the above.
15. The method of claim 1 wherein said metal nanoparticles are silver nanoparticles.
16. The method of claim 1 wherein said metal salt have low water solubility.
17. The method of claim 1 , wherein said metal salt have a solubility of up to 5% w/w at a temperature of 100° C.
18. The method of claim 1 wherein said metal salt is selected from silver acetate, silver sulfate, silver carbonate, and mixtures of any of the above.
19. The method of claim 1 wherein said metal salt is a metal acetate salt.
20. The method of claim 19 wherein said metal acetate salt is silver acetate.
21. The method of claim 1 wherein the content of said metal salt in said suspension is in the range of 1.0 to 50 wt %.
22. The method of claim 1 wherein the concentration of said metal nanopraticles in said dispersion is in the range 0.5-35 wt %, based on the total weight of the dispersion.
23. The method of claim 1 wherein the particle size of said nanoparticles is below 20 nm in diameter.
24. The method of claim 1 wherein said metal salt is silver acetate and said water soluble polymer is polypyrrole.
25. The method of claim 1 wherein the concentration of said water soluble polymer is in the range of 0.1-10 wt %.
26. The method of claim 1 wherein the weight ratio of said water soluble polymer to said metal is below 0.1:1.
27. The method of claim 1 wherein the weight ratio of said water soluble polymer to said metal is in the range 0.01:1-0.06:1.
28. The method of claim 1 wherein said chemical reducer is selected from tri-sodium citrate, ascorbic acid, di-sodium tartrate, hydrazine, sodium borohydride, and mixtures of any of the above.
29. The method of claim 1 further comprising adding a colorant to said dispersion.
30. The method according to claim 1 further comprising adding to said dispersion an additive selected from humectants, binders, surfactants, fungicides, rheology modifiers, pH adjusting agents, co-solvents, and mixtures thereof.
31. The method according to claim 1 , further comprising a step of preparing an ink composition, a paint, or a coating.
32. The method according to claim 31 wherein said ink composition is for use in ink-jet printing.
33. The method according to claim 1 , further comprising a step of forming a conductive pattern by deposition of said dispersion on a substrate and optionally followed by sintering.
34. The method according to claim 1 further comprising placing or jetting drops of the dispersion onto a substrate to obtain conductive rings.
35. The method according to claim 34 wherein said conductive rings have high electrical conductivity at room temperature.
36. The method according to claim 1 further comprising dispensing a plurality of drops of the dispersion onto a substrate to form arrays of conductive rings.
37. A method for preparing an aqueous-based dispersion of metal nanoparticles, comprising:
(a) providing an aqueous suspension of a metal salt, wherein the concentration of the soluble metal salt in the suspension is below its saturation value;
(b) pre-reducing said metal salt suspension by a water soluble polymer capable of metal reduction to form metal nuclei; and
(c) adding a chemical reducer to form metal nanoparticles in dispersion.